Merge branch 'master' into i110/inspect-recursion

25 files changed, 3902 insertions, 3973 deletions

diff --git a/src/array.c b/src/array.c
index 2152e292d..8cf813743 100644
--- a/src/array.c
+++ b/src/array.c
@@ -120,9 +120,7 @@ ary_fill_with_nil(mrb_value *ptr, mrb_int size)
 static void
 ary_modify_check(mrb_state *mrb, struct RArray *a)
 {
-  if (MRB_FROZEN_P(a)) {
-    mrb_raise(mrb, E_FROZEN_ERROR, "can't modify frozen array");
-  }
+  mrb_check_frozen(mrb, a);
 }
 
 static void
@@ -231,7 +229,7 @@ ary_expand_capa(mrb_state *mrb, struct RArray *a, mrb_int len)
 static void
 ary_shrink_capa(mrb_state *mrb, struct RArray *a)
 {
-  
+
   mrb_int capa;
 
   if (ARY_EMBED_P(a)) return;
@@ -853,14 +851,14 @@ static mrb_value
 mrb_ary_aget(mrb_state *mrb, mrb_value self)
 {
   struct RArray *a = mrb_ary_ptr(self);
-  mrb_int i, len, alen = ARY_LEN(a);
+  mrb_int i, len, alen;
   mrb_value index;
 
   if (mrb_get_args(mrb, "o|i", &index, &len) == 1) {
     switch (mrb_type(index)) {
       /* a[n..m] */
     case MRB_TT_RANGE:
-      if (mrb_range_beg_len(mrb, index, &i, &len, alen, TRUE) == 1) {
+      if (mrb_range_beg_len(mrb, index, &i, &len, ARY_LEN(a), TRUE) == MRB_RANGE_OK) {
         return ary_subseq(mrb, a, i, len);
       }
       else {
@@ -874,6 +872,7 @@ mrb_ary_aget(mrb_state *mrb, mrb_value self)
   }
 
   i = aget_index(mrb, index);
+  alen = ARY_LEN(a);
   if (i < 0) i += alen;
   if (i < 0 || alen < i) return mrb_nil_value();
   if (len < 0) return mrb_nil_value();
@@ -928,13 +927,13 @@ mrb_ary_aset(mrb_state *mrb, mrb_value self)
   if (mrb_get_args(mrb, "oo|o", &v1, &v2, &v3) == 2) {
     /* a[n..m] = v */
     switch (mrb_range_beg_len(mrb, v1, &i, &len, RARRAY_LEN(self), FALSE)) {
-    case 0:                   /* not range */
+    case MRB_RANGE_TYPE_MISMATCH:
       mrb_ary_set(mrb, self, aget_index(mrb, v1), v2);
       break;
-    case 1:                   /* range */
+    case MRB_RANGE_OK:
       mrb_ary_splice(mrb, self, i, len, v2);
       break;
-    case 2:                   /* out of range */
+    case MRB_RANGE_OUT:
       mrb_raisef(mrb, E_RANGE_ERROR, "%S out of range", v1);
       break;
     }
@@ -953,9 +952,10 @@ mrb_ary_delete_at(mrb_state *mrb, mrb_value self)
   mrb_int   index;
   mrb_value val;
   mrb_value *ptr;
-  mrb_int len, alen = ARY_LEN(a);
+  mrb_int len, alen;
 
   mrb_get_args(mrb, "i", &index);
+  alen = ARY_LEN(a);
   if (index < 0) index += alen;
   if (index < 0 || alen <= index) return mrb_nil_value();
 
@@ -980,16 +980,17 @@ static mrb_value
 mrb_ary_first(mrb_state *mrb, mrb_value self)
 {
   struct RArray *a = mrb_ary_ptr(self);
-  mrb_int size, alen = ARY_LEN(a);
+  mrb_int size, alen;
 
   if (mrb_get_argc(mrb) == 0) {
-    return (alen > 0)? ARY_PTR(a)[0]: mrb_nil_value();
+    return (ARY_LEN(a) > 0)? ARY_PTR(a)[0]: mrb_nil_value();
   }
   mrb_get_args(mrb, "|i", &size);
   if (size < 0) {
     mrb_raise(mrb, E_ARGUMENT_ERROR, "negative array size");
   }
 
+  alen = ARY_LEN(a);
   if (size > alen) size = alen;
   if (ARY_SHARED_P(a)) {
     return ary_subseq(mrb, a, 0, size);
@@ -1001,10 +1002,13 @@ static mrb_value
 mrb_ary_last(mrb_state *mrb, mrb_value self)
 {
   struct RArray *a = mrb_ary_ptr(self);
-  mrb_int size, alen = ARY_LEN(a);
+  mrb_int n, size, alen;
 
-  if (mrb_get_args(mrb, "|i", &size) == 0)
-    return (alen > 0)? ARY_PTR(a)[alen - 1]: mrb_nil_value();
+  n = mrb_get_args(mrb, "|i", &size);
+  alen = ARY_LEN(a);
+  if (n == 0) {
+    return (alen > 0) ? ARY_PTR(a)[alen - 1]: mrb_nil_value();
+  }
 
   if (size < 0) {
     mrb_raise(mrb, E_ARGUMENT_ERROR, "negative array size");
@@ -1052,7 +1056,7 @@ mrb_ary_rindex_m(mrb_state *mrb, mrb_value self)
 MRB_API mrb_value
 mrb_ary_splat(mrb_state *mrb, mrb_value v)
 {
-  mrb_value a, recv_class;
+  mrb_value a;
 
   if (mrb_array_p(v)) {
     return v;
@@ -1063,22 +1067,11 @@ mrb_ary_splat(mrb_state *mrb, mrb_value v)
   }
 
   a = mrb_funcall(mrb, v, "to_a", 0);
-  if (mrb_array_p(a)) {
-    return a;
-  }
-  else if (mrb_nil_p(a)) {
+  if (mrb_nil_p(a)) {
     return mrb_ary_new_from_values(mrb, 1, &v);
   }
-  else {
-    recv_class = mrb_obj_value(mrb_obj_class(mrb, v));
-    mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S to Array (%S#to_a gives %S)",
-      recv_class,
-      recv_class,
-      mrb_obj_value(mrb_obj_class(mrb, a))
-    );
-    /* not reached */
-    return mrb_undef_value();
-  }
+  mrb_ensure_array_type(mrb, a);
+  return a;
 }
 
 static mrb_value
@@ -1108,6 +1101,13 @@ mrb_ary_clear(mrb_state *mrb, mrb_value self)
 }
 
 static mrb_value
+mrb_ary_clear_m(mrb_state *mrb, mrb_value self)
+{
+  mrb_get_args(mrb, "");
+  return mrb_ary_clear(mrb, self);
+}
+
+static mrb_value
 mrb_ary_empty_p(mrb_state *mrb, mrb_value self)
 {
   struct RArray *a = mrb_ary_ptr(self);
@@ -1116,12 +1116,6 @@ mrb_ary_empty_p(mrb_state *mrb, mrb_value self)
 }
 
 MRB_API mrb_value
-mrb_check_array_type(mrb_state *mrb, mrb_value ary)
-{
-  return mrb_check_convert_type(mrb, ary, MRB_TT_ARRAY, "Array", "to_ary");
-}
-
-MRB_API mrb_value
 mrb_ary_entry(mrb_value ary, mrb_int offset)
 {
   if (offset < 0) {
@@ -1174,7 +1168,7 @@ join_ary(mrb_state *mrb, mrb_value ary, mrb_value sep, mrb_value list)
           val = tmp;
           goto str_join;
         }
-        tmp = mrb_check_convert_type(mrb, val, MRB_TT_ARRAY, "Array", "to_ary");
+        tmp = mrb_check_array_type(mrb, val);
         if (!mrb_nil_p(tmp)) {
           val = tmp;
           goto ary_join;
@@ -1268,41 +1262,39 @@ mrb_init_array(mrb_state *mrb)
 {
   struct RClass *a;
 
-  mrb->array_class = a = mrb_define_class(mrb, "Array", mrb->object_class);            /* 15.2.12 */
+  mrb->array_class = a = mrb_define_class(mrb, "Array", mrb->object_class);              /* 15.2.12 */
   MRB_SET_INSTANCE_TT(a, MRB_TT_ARRAY);
 
-  mrb_define_class_method(mrb, a, "[]",        mrb_ary_s_create,     MRB_ARGS_ANY());  /* 15.2.12.4.1 */
-
-  mrb_define_method(mrb, a, "+",               mrb_ary_plus,         MRB_ARGS_REQ(1)); /* 15.2.12.5.1  */
-  mrb_define_method(mrb, a, "*",               mrb_ary_times,        MRB_ARGS_REQ(1)); /* 15.2.12.5.2  */
-  mrb_define_method(mrb, a, "<<",              mrb_ary_push_m,       MRB_ARGS_REQ(1)); /* 15.2.12.5.3  */
-  mrb_define_method(mrb, a, "[]",              mrb_ary_aget,         MRB_ARGS_ANY());  /* 15.2.12.5.4  */
-  mrb_define_method(mrb, a, "[]=",             mrb_ary_aset,         MRB_ARGS_ANY());  /* 15.2.12.5.5  */
-  mrb_define_method(mrb, a, "clear",           mrb_ary_clear,        MRB_ARGS_NONE()); /* 15.2.12.5.6  */
-  mrb_define_method(mrb, a, "concat",          mrb_ary_concat_m,     MRB_ARGS_REQ(1)); /* 15.2.12.5.8  */
-  mrb_define_method(mrb, a, "delete_at",       mrb_ary_delete_at,    MRB_ARGS_REQ(1)); /* 15.2.12.5.9  */
-  mrb_define_method(mrb, a, "empty?",          mrb_ary_empty_p,      MRB_ARGS_NONE()); /* 15.2.12.5.12 */
-  mrb_define_method(mrb, a, "first",           mrb_ary_first,        MRB_ARGS_OPT(1)); /* 15.2.12.5.13 */
-  mrb_define_method(mrb, a, "index",           mrb_ary_index_m,      MRB_ARGS_REQ(1)); /* 15.2.12.5.14 */
-  mrb_define_method(mrb, a, "initialize_copy", mrb_ary_replace_m,    MRB_ARGS_REQ(1)); /* 15.2.12.5.16 */
-  mrb_define_method(mrb, a, "join",            mrb_ary_join_m,       MRB_ARGS_ANY());  /* 15.2.12.5.17 */
-  mrb_define_method(mrb, a, "last",            mrb_ary_last,         MRB_ARGS_ANY());  /* 15.2.12.5.18 */
-  mrb_define_method(mrb, a, "length",          mrb_ary_size,         MRB_ARGS_NONE()); /* 15.2.12.5.19 */
-  mrb_define_method(mrb, a, "pop",             mrb_ary_pop,          MRB_ARGS_NONE()); /* 15.2.12.5.21 */
-  mrb_define_method(mrb, a, "push",            mrb_ary_push_m,       MRB_ARGS_ANY());  /* 15.2.12.5.22 */
-  mrb_define_method(mrb, a, "append",          mrb_ary_push_m,       MRB_ARGS_ANY());
-  mrb_define_method(mrb, a, "replace",         mrb_ary_replace_m,    MRB_ARGS_REQ(1)); /* 15.2.12.5.23 */
-  mrb_define_method(mrb, a, "reverse",         mrb_ary_reverse,      MRB_ARGS_NONE()); /* 15.2.12.5.24 */
-  mrb_define_method(mrb, a, "reverse!",        mrb_ary_reverse_bang, MRB_ARGS_NONE()); /* 15.2.12.5.25 */
-  mrb_define_method(mrb, a, "rindex",          mrb_ary_rindex_m,     MRB_ARGS_REQ(1)); /* 15.2.12.5.26 */
-  mrb_define_method(mrb, a, "shift",           mrb_ary_shift,        MRB_ARGS_NONE()); /* 15.2.12.5.27 */
-  mrb_define_method(mrb, a, "size",            mrb_ary_size,         MRB_ARGS_NONE()); /* 15.2.12.5.28 */
-  mrb_define_method(mrb, a, "slice",           mrb_ary_aget,         MRB_ARGS_ANY());  /* 15.2.12.5.29 */
-  mrb_define_method(mrb, a, "unshift",         mrb_ary_unshift_m,    MRB_ARGS_ANY());  /* 15.2.12.5.30 */
-  mrb_define_method(mrb, a, "prepend",         mrb_ary_unshift_m,    MRB_ARGS_ANY());
+  mrb_define_class_method(mrb, a, "[]",        mrb_ary_s_create,     MRB_ARGS_ANY());    /* 15.2.12.4.1 */
+
+  mrb_define_method(mrb, a, "+",               mrb_ary_plus,         MRB_ARGS_REQ(1));   /* 15.2.12.5.1  */
+  mrb_define_method(mrb, a, "*",               mrb_ary_times,        MRB_ARGS_REQ(1));   /* 15.2.12.5.2  */
+  mrb_define_method(mrb, a, "<<",              mrb_ary_push_m,       MRB_ARGS_REQ(1));   /* 15.2.12.5.3  */
+  mrb_define_method(mrb, a, "[]",              mrb_ary_aget,         MRB_ARGS_ARG(1,1)); /* 15.2.12.5.4  */
+  mrb_define_method(mrb, a, "[]=",             mrb_ary_aset,         MRB_ARGS_ARG(2,1)); /* 15.2.12.5.5  */
+  mrb_define_method(mrb, a, "clear",           mrb_ary_clear_m,      MRB_ARGS_NONE());   /* 15.2.12.5.6  */
+  mrb_define_method(mrb, a, "concat",          mrb_ary_concat_m,     MRB_ARGS_REQ(1));   /* 15.2.12.5.8  */
+  mrb_define_method(mrb, a, "delete_at",       mrb_ary_delete_at,    MRB_ARGS_REQ(1));   /* 15.2.12.5.9  */
+  mrb_define_method(mrb, a, "empty?",          mrb_ary_empty_p,      MRB_ARGS_NONE());   /* 15.2.12.5.12 */
+  mrb_define_method(mrb, a, "first",           mrb_ary_first,        MRB_ARGS_OPT(1));   /* 15.2.12.5.13 */
+  mrb_define_method(mrb, a, "index",           mrb_ary_index_m,      MRB_ARGS_REQ(1));   /* 15.2.12.5.14 */
+  mrb_define_method(mrb, a, "initialize_copy", mrb_ary_replace_m,    MRB_ARGS_REQ(1));   /* 15.2.12.5.16 */
+  mrb_define_method(mrb, a, "join",            mrb_ary_join_m,       MRB_ARGS_OPT(1));   /* 15.2.12.5.17 */
+  mrb_define_method(mrb, a, "last",            mrb_ary_last,         MRB_ARGS_OPT(1));   /* 15.2.12.5.18 */
+  mrb_define_method(mrb, a, "length",          mrb_ary_size,         MRB_ARGS_NONE());   /* 15.2.12.5.19 */
+  mrb_define_method(mrb, a, "pop",             mrb_ary_pop,          MRB_ARGS_NONE());   /* 15.2.12.5.21 */
+  mrb_define_method(mrb, a, "push",            mrb_ary_push_m,       MRB_ARGS_ANY());    /* 15.2.12.5.22 */
+  mrb_define_method(mrb, a, "replace",         mrb_ary_replace_m,    MRB_ARGS_REQ(1));   /* 15.2.12.5.23 */
+  mrb_define_method(mrb, a, "reverse",         mrb_ary_reverse,      MRB_ARGS_NONE());   /* 15.2.12.5.24 */
+  mrb_define_method(mrb, a, "reverse!",        mrb_ary_reverse_bang, MRB_ARGS_NONE());   /* 15.2.12.5.25 */
+  mrb_define_method(mrb, a, "rindex",          mrb_ary_rindex_m,     MRB_ARGS_REQ(1));   /* 15.2.12.5.26 */
+  mrb_define_method(mrb, a, "shift",           mrb_ary_shift,        MRB_ARGS_NONE());   /* 15.2.12.5.27 */
+  mrb_define_method(mrb, a, "size",            mrb_ary_size,         MRB_ARGS_NONE());   /* 15.2.12.5.28 */
+  mrb_define_method(mrb, a, "slice",           mrb_ary_aget,         MRB_ARGS_ARG(1,1)); /* 15.2.12.5.29 */
+  mrb_define_method(mrb, a, "unshift",         mrb_ary_unshift_m,    MRB_ARGS_ANY());    /* 15.2.12.5.30 */
 
   mrb_define_method(mrb, a, "__ary_eq",        mrb_ary_eq,           MRB_ARGS_REQ(1));
   mrb_define_method(mrb, a, "__ary_cmp",       mrb_ary_cmp,          MRB_ARGS_REQ(1));
-  mrb_define_method(mrb, a, "__ary_index",     mrb_ary_index_m,      MRB_ARGS_REQ(1)); /* kept for mruby-array-ext */
+  mrb_define_method(mrb, a, "__ary_index",     mrb_ary_index_m,      MRB_ARGS_REQ(1));   /* kept for mruby-array-ext */
   mrb_define_method(mrb, a, "__svalue",        mrb_ary_svalue,       MRB_ARGS_NONE());
 }
diff --git a/src/backtrace.c b/src/backtrace.c
index 57ae7fd7f..991a67d00 100644
--- a/src/backtrace.c
+++ b/src/backtrace.c
@@ -16,24 +16,24 @@
 #include <mruby/data.h>
 
 struct backtrace_location {
-  int lineno;
-  const char *filename;
+  int32_t lineno;
   mrb_sym method_id;
+  const char *filename;
 };
 
-typedef void (*each_backtrace_func)(mrb_state*, struct backtrace_location*, void*);
+typedef void (*each_backtrace_func)(mrb_state*, const struct backtrace_location*, void*);
 
 static const mrb_data_type bt_type = { "Backtrace", mrb_free };
 
 static void
 each_backtrace(mrb_state *mrb, ptrdiff_t ciidx, mrb_code *pc0, each_backtrace_func func, void *data)
 {
-  ptrdiff_t i, j;
+  ptrdiff_t i;
 
   if (ciidx >= mrb->c->ciend - mrb->c->cibase)
     ciidx = 10; /* ciidx is broken... */
 
-  for (i=ciidx, j=0; i >= 0; i--,j++) {
+  for (i=ciidx; i >= 0; i--) {
     struct backtrace_location loc;
     mrb_callinfo *ci;
     mrb_irep *irep;
@@ -57,11 +57,11 @@ each_backtrace(mrb_state *mrb, ptrdiff_t ciidx, mrb_code *pc0, each_backtrace_fu
     else {
       pc = pc0;
     }
-    loc.filename = mrb_debug_get_filename(irep, pc - irep->iseq);
-    loc.lineno = mrb_debug_get_line(irep, pc - irep->iseq);
 
+    loc.lineno = mrb_debug_get_line(mrb, irep, pc - irep->iseq);
     if (loc.lineno == -1) continue;
 
+    loc.filename = mrb_debug_get_filename(mrb, irep, pc - irep->iseq);
     if (!loc.filename) {
       loc.filename = "(unknown)";
     }
@@ -80,8 +80,6 @@ print_backtrace(mrb_state *mrb, mrb_value backtrace)
   mrb_int n;
   FILE *stream = stderr;
 
-  if (!mrb_array_p(backtrace)) return;
-
   n = RARRAY_LEN(backtrace) - 1;
   if (n == 0) return;
 
@@ -96,7 +94,7 @@ print_backtrace(mrb_state *mrb, mrb_value backtrace)
 }
 
 static int
-packed_bt_len(struct backtrace_location *bt, int n)
+packed_bt_len(const struct backtrace_location *bt, int n)
 {
   int len = 0;
   int i;
@@ -113,7 +111,7 @@ static void
 print_packed_backtrace(mrb_state *mrb, mrb_value packed)
 {
   FILE *stream = stderr;
-  struct backtrace_location *bt;
+  const struct backtrace_location *bt;
   int n, i;
   int ai = mrb_gc_arena_save(mrb);
 
@@ -124,7 +122,7 @@ print_packed_backtrace(mrb_state *mrb, mrb_value packed)
   if (packed_bt_len(bt, n) == 0) return;
   fprintf(stream, "trace (most recent call last):\n");
   for (i = 0; i<n; i++) {
-    struct backtrace_location *entry = &bt[n-i-1];
+    const struct backtrace_location *entry = &bt[n-i-1];
     if (entry->filename == NULL) continue;
     fprintf(stream, "\t[%d] %s:%d", i, entry->filename, entry->lineno);
     if (entry->method_id != 0) {
@@ -172,7 +170,7 @@ mrb_print_backtrace(mrb_state *mrb)
 
 static void
 count_backtrace_i(mrb_state *mrb,
-                 struct backtrace_location *loc,
+                 const struct backtrace_location *loc,
                  void *data)
 {
   int *lenp = (int*)data;
@@ -183,7 +181,7 @@ count_backtrace_i(mrb_state *mrb,
 
 static void
 pack_backtrace_i(mrb_state *mrb,
-                 struct backtrace_location *loc,
+                 const struct backtrace_location *loc,
                  void *data)
 {
   struct backtrace_location **pptr = (struct backtrace_location**)data;
@@ -206,7 +204,6 @@ packed_backtrace(mrb_state *mrb)
   each_backtrace(mrb, ciidx, mrb->c->ci->pc, count_backtrace_i, &len);
   size = len * sizeof(struct backtrace_location);
   ptr = mrb_malloc(mrb, size);
-  if (ptr) memset(ptr, 0, size);
   backtrace = mrb_data_object_alloc(mrb, NULL, ptr, &bt_type);
   backtrace->flags = (unsigned int)len;
   each_backtrace(mrb, ciidx, mrb->c->ci->pc, pack_backtrace_i, &ptr);
@@ -230,7 +227,7 @@ mrb_keep_backtrace(mrb_state *mrb, mrb_value exc)
 mrb_value
 mrb_unpack_backtrace(mrb_state *mrb, mrb_value backtrace)
 {
-  struct backtrace_location *bt;
+  const struct backtrace_location *bt;
   mrb_int n, i;
   int ai;
 
@@ -245,7 +242,7 @@ mrb_unpack_backtrace(mrb_state *mrb, mrb_value backtrace)
   backtrace = mrb_ary_new_capa(mrb, n);
   ai = mrb_gc_arena_save(mrb);
   for (i = 0; i < n; i++) {
-    struct backtrace_location *entry = &bt[i];
+    const struct backtrace_location *entry = &bt[i];
     mrb_value btline;
 
     if (entry->filename == NULL) continue;
diff --git a/src/class.c b/src/class.c
index c761f46af..edee95678 100644
--- a/src/class.c
+++ b/src/class.c
@@ -65,16 +65,22 @@ mrb_class_name_class(mrb_state *mrb, struct RClass *outer, struct RClass *c, mrb
   else {
     name = mrb_class_path(mrb, outer);
     if (mrb_nil_p(name)) {      /* unnamed outer class */
-      if (outer != mrb->object_class) {
-        mrb_obj_iv_set(mrb, (struct RObject*)c, mrb_intern_lit(mrb, "__outer__"),
-                       mrb_obj_value(outer));
+      if (outer != mrb->object_class && outer != c) {
+        mrb_obj_iv_set_force(mrb, (struct RObject*)c, mrb_intern_lit(mrb, "__outer__"),
+                             mrb_obj_value(outer));
       }
       return;
     }
     mrb_str_cat_cstr(mrb, name, "::");
     mrb_str_cat_cstr(mrb, name, mrb_sym2name(mrb, id));
   }
-  mrb_obj_iv_set(mrb, (struct RObject*)c, nsym, name);
+  mrb_obj_iv_set_force(mrb, (struct RObject*)c, nsym, name);
+}
+
+mrb_bool
+mrb_const_name_p(mrb_state *mrb, const char *name, mrb_int len)
+{
+  return len > 0 && ISUPPER(name[0]) && mrb_ident_p(name+1, len-1);
 }
 
 static void
@@ -93,7 +99,7 @@ prepare_singleton_class(mrb_state *mrb, struct RBasic *o)
 
   if (o->c->tt == MRB_TT_SCLASS) return;
   sc = (struct RClass*)mrb_obj_alloc(mrb, MRB_TT_SCLASS, mrb->class_class);
-  sc->flags |= MRB_FLAG_IS_INHERITED;
+  sc->flags |= MRB_FL_CLASS_IS_INHERITED;
   sc->mt = kh_init(mt, mrb);
   sc->iv = 0;
   if (o->tt == MRB_TT_CLASS) {
@@ -120,6 +126,20 @@ prepare_singleton_class(mrb_state *mrb, struct RBasic *o)
   mrb_field_write_barrier(mrb, (struct RBasic*)o, (struct RBasic*)sc);
   mrb_field_write_barrier(mrb, (struct RBasic*)sc, (struct RBasic*)o);
   mrb_obj_iv_set(mrb, (struct RObject*)sc, mrb_intern_lit(mrb, "__attached__"), mrb_obj_value(o));
+  sc->flags |= o->flags & MRB_FL_OBJ_IS_FROZEN;
+}
+
+static mrb_value
+class_name_str(mrb_state *mrb, struct RClass* c)
+{
+  mrb_value path = mrb_class_path(mrb, c);
+  if (mrb_nil_p(path)) {
+    path = c->tt == MRB_TT_MODULE ? mrb_str_new_lit(mrb, "#<Module:") :
+                                    mrb_str_new_lit(mrb, "#<Class:");
+    mrb_str_concat(mrb, path, mrb_ptr_to_str(mrb, c));
+    mrb_str_cat_lit(mrb, path, ">");
+  }
+  return path;
 }
 
 static struct RClass*
@@ -275,7 +295,7 @@ mrb_class_inherited(mrb_state *mrb, struct RClass *super, struct RClass *klass)
 
   if (!super)
     super = mrb->object_class;
-  super->flags |= MRB_FLAG_IS_INHERITED;
+  super->flags |= MRB_FL_CLASS_IS_INHERITED;
   s = mrb_obj_value(super);
   mc_clear_by_class(mrb, klass);
   mid = mrb_intern_lit(mrb, "inherited");
@@ -428,12 +448,7 @@ mrb_define_method_raw(mrb_state *mrb, struct RClass *c, mrb_sym mid, mrb_method_
   MRB_CLASS_ORIGIN(c);
   h = c->mt;
 
-  if (MRB_FROZEN_P(c)) {
-    if (c->tt == MRB_TT_MODULE)
-      mrb_raise(mrb, E_FROZEN_ERROR, "can't modify frozen module");
-    else
-      mrb_raise(mrb, E_FROZEN_ERROR, "can't modify frozen class");
-  }
+  mrb_check_frozen(mrb, c);
   if (!h) h = c->mt = kh_init(mt, mrb);
   k = kh_put(mt, mrb, h, mid);
   kh_value(h, k) = m;
@@ -471,15 +486,11 @@ mrb_define_method(mrb_state *mrb, struct RClass *c, const char *name, mrb_func_t
 MRB_API void
 mrb_notimplement(mrb_state *mrb)
 {
-  const char *str;
-  mrb_int len;
   mrb_callinfo *ci = mrb->c->ci;
 
   if (ci->mid) {
-    str = mrb_sym2name_len(mrb, ci->mid, &len);
-    mrb_raisef(mrb, E_NOTIMP_ERROR,
-      "%S() function is unimplemented on this machine",
-      mrb_str_new_static(mrb, str, (size_t)len));
+    mrb_value str = mrb_sym2str(mrb, ci->mid);
+    mrb_raisef(mrb, E_NOTIMP_ERROR, "%S() function is unimplemented on this machine", str);
   }
 }
 
@@ -492,52 +503,34 @@ mrb_notimplement_m(mrb_state *mrb, mrb_value self)
   return mrb_nil_value();
 }
 
-static mrb_value
-check_type(mrb_state *mrb, mrb_value val, enum mrb_vtype t, const char *c, const char *m)
-{
-  mrb_value tmp;
-
-  tmp = mrb_check_convert_type(mrb, val, t, c, m);
-  if (mrb_nil_p(tmp)) {
-    mrb_raisef(mrb, E_TYPE_ERROR, "expected %S", mrb_str_new_cstr(mrb, c));
-  }
-  return tmp;
-}
+#define CHECK_TYPE(mrb, val, t, c) do { \
+  if (mrb_type(val) != (t)) {\
+    mrb_raisef(mrb, E_TYPE_ERROR, "expected %S", mrb_str_new_lit(mrb, c));\
+  }\
+} while (0)
 
 static mrb_value
 to_str(mrb_state *mrb, mrb_value val)
 {
-  return check_type(mrb, val, MRB_TT_STRING, "String", "to_str");
+  CHECK_TYPE(mrb, val, MRB_TT_STRING, "String");
+  return val;
 }
 
 static mrb_value
 to_ary(mrb_state *mrb, mrb_value val)
 {
-  return check_type(mrb, val, MRB_TT_ARRAY, "Array", "to_ary");
+  CHECK_TYPE(mrb, val, MRB_TT_ARRAY, "Array");
+  return val;
 }
 
 static mrb_value
 to_hash(mrb_state *mrb, mrb_value val)
 {
-  return check_type(mrb, val, MRB_TT_HASH, "Hash", "to_hash");
+  CHECK_TYPE(mrb, val, MRB_TT_HASH, "Hash");
+  return val;
 }
 
-static mrb_sym
-to_sym(mrb_state *mrb, mrb_value ss)
-{
-  if (mrb_type(ss) == MRB_TT_SYMBOL) {
-    return mrb_symbol(ss);
-  }
-  else if (mrb_string_p(ss)) {
-    return mrb_intern_str(mrb, to_str(mrb, ss));
-  }
-  else {
-    mrb_value obj = mrb_funcall(mrb, ss, "inspect", 0);
-    mrb_raisef(mrb, E_TYPE_ERROR, "%S is not a symbol", obj);
-    /* not reached */
-    return 0;
-  }
-}
+#define to_sym(mrb, ss) mrb_obj_to_sym(mrb, ss)
 
 MRB_API mrb_int
 mrb_get_argc(mrb_state *mrb)
@@ -580,20 +573,20 @@ mrb_get_argv(mrb_state *mrb)
     string  mruby type     C type                 note
     ----------------------------------------------------------------------------------------------
     o:      Object         [mrb_value]
-    C:      class/module   [mrb_value]
+    C:      Class/Module   [mrb_value]
     S:      String         [mrb_value]            when ! follows, the value may be nil
     A:      Array          [mrb_value]            when ! follows, the value may be nil
     H:      Hash           [mrb_value]            when ! follows, the value may be nil
     s:      String         [char*,mrb_int]        Receive two arguments; s! gives (NULL,0) for nil
     z:      String         [char*]                NUL terminated string; z! gives NULL for nil
     a:      Array          [mrb_value*,mrb_int]   Receive two arguments; a! gives (NULL,0) for nil
-    f:      Float          [mrb_float]
-    i:      Integer        [mrb_int]
-    b:      Boolean        [mrb_bool]
-    n:      Symbol         [mrb_sym]
-    d:      Data           [void*,mrb_data_type const] 2nd argument will be used to check data type so it won't be modified
-    I:      Inline struct  [void*]
-    &:      Block          [mrb_value]            &! raises exception if no block given
+    f:      Fixnum/Float   [mrb_float]
+    i:      Fixnum/Float   [mrb_int]
+    b:      boolean        [mrb_bool]
+    n:      String/Symbol  [mrb_sym]
+    d:      data           [void*,mrb_data_type const] 2nd argument will be used to check data type so it won't be modified; when ! follows, the value may be nil
+    I:      inline struct  [void*]
+    &:      block          [mrb_value]            &! raises exception if no block given
     *:      rest argument  [mrb_value*,mrb_int]   The rest of the arguments as an array; *! avoid copy of the stack
     |:      optional                              Following arguments are optional
     ?:      optional given [mrb_bool]             true if preceding argument (optional) is given
@@ -851,29 +844,7 @@ mrb_get_args(mrb_state *mrb, const char *format, ...)
 
         p = va_arg(ap, mrb_int*);
         if (i < argc) {
-          switch (mrb_type(ARGV[arg_i])) {
-            case MRB_TT_FIXNUM:
-              *p = mrb_fixnum(ARGV[arg_i]);
-              break;
-#ifndef MRB_WITHOUT_FLOAT
-            case MRB_TT_FLOAT:
-              {
-                mrb_float f = mrb_float(ARGV[arg_i]);
-
-                if (!FIXABLE_FLOAT(f)) {
-                  mrb_raise(mrb, E_RANGE_ERROR, "float too big for int");
-                }
-                *p = (mrb_int)f;
-              }
-              break;
-#endif
-            case MRB_TT_STRING:
-              mrb_raise(mrb, E_TYPE_ERROR, "no implicit conversion of String into Integer");
-              break;
-            default:
-              *p = mrb_fixnum(mrb_Integer(mrb, ARGV[arg_i]));
-              break;
-          }
+          *p = mrb_fixnum(mrb_to_int(mrb, ARGV[arg_i]));
           arg_i++;
           i++;
         }
@@ -1061,7 +1032,7 @@ include_module_at(mrb_state *mrb, struct RClass *c, struct RClass *ins_pos, stru
   while (m) {
     int superclass_seen = 0;
 
-    if (m->flags & MRB_FLAG_IS_PREPENDED)
+    if (m->flags & MRB_FL_CLASS_IS_PREPENDED)
       goto skip;
 
     if (klass_mt && klass_mt == m->mt)
@@ -1084,7 +1055,7 @@ include_module_at(mrb_state *mrb, struct RClass *c, struct RClass *ins_pos, stru
     }
 
     ic = include_class_new(mrb, m, ins_pos->super);
-    m->flags |= MRB_FLAG_IS_INHERITED;
+    m->flags |= MRB_FL_CLASS_IS_INHERITED;
     ins_pos->super = ic;
     mrb_field_write_barrier(mrb, (struct RBasic*)ins_pos, (struct RBasic*)ic);
     mc_clear_by_class(mrb, ins_pos);
@@ -1099,8 +1070,8 @@ include_module_at(mrb_state *mrb, struct RClass *c, struct RClass *ins_pos, stru
 MRB_API void
 mrb_include_module(mrb_state *mrb, struct RClass *c, struct RClass *m)
 {
-  int changed = include_module_at(mrb, c, find_origin(c), m, 1);
-  if (changed < 0) {
+  mrb_check_frozen(mrb, c);
+  if (include_module_at(mrb, c, find_origin(c), m, 1) < 0) {
     mrb_raise(mrb, E_ARGUMENT_ERROR, "cyclic include detected");
   }
 }
@@ -1111,15 +1082,16 @@ mrb_prepend_module(mrb_state *mrb, struct RClass *c, struct RClass *m)
   struct RClass *origin;
   int changed = 0;
 
-  if (!(c->flags & MRB_FLAG_IS_PREPENDED)) {
+  mrb_check_frozen(mrb, c);
+  if (!(c->flags & MRB_FL_CLASS_IS_PREPENDED)) {
     origin = (struct RClass*)mrb_obj_alloc(mrb, MRB_TT_ICLASS, c);
-    origin->flags |= MRB_FLAG_IS_ORIGIN | MRB_FLAG_IS_INHERITED;
+    origin->flags |= MRB_FL_CLASS_IS_ORIGIN | MRB_FL_CLASS_IS_INHERITED;
     origin->super = c->super;
     c->super = origin;
     origin->mt = c->mt;
     c->mt = kh_init(mt, mrb);
     mrb_field_write_barrier(mrb, (struct RBasic*)c, (struct RBasic*)origin);
-    c->flags |= MRB_FLAG_IS_PREPENDED;
+    c->flags |= MRB_FL_CLASS_IS_PREPENDED;
   }
   changed = include_module_at(mrb, c, c, m, 0);
   if (changed < 0) {
@@ -1196,7 +1168,7 @@ mrb_mod_ancestors(mrb_state *mrb, mrb_value self)
     if (c->tt == MRB_TT_ICLASS) {
       mrb_ary_push(mrb, result, mrb_obj_value(c->c));
     }
-    else if (!(c->flags & MRB_FLAG_IS_PREPENDED)) {
+    else if (!(c->flags & MRB_FL_CLASS_IS_PREPENDED)) {
       mrb_ary_push(mrb, result, mrb_obj_value(c));
     }
     c = c->super;
@@ -1217,27 +1189,6 @@ mrb_mod_extend_object(mrb_state *mrb, mrb_value mod)
 }
 
 static mrb_value
-mrb_mod_included_modules(mrb_state *mrb, mrb_value self)
-{
-  mrb_value result;
-  struct RClass *c = mrb_class_ptr(self);
-  struct RClass *origin = c;
-
-  MRB_CLASS_ORIGIN(origin);
-  result = mrb_ary_new(mrb);
-  while (c) {
-    if (c != origin && c->tt == MRB_TT_ICLASS) {
-      if (c->c->tt == MRB_TT_MODULE) {
-        mrb_ary_push(mrb, result, mrb_obj_value(c->c));
-      }
-    }
-    c = c->super;
-  }
-
-  return result;
-}
-
-static mrb_value
 mrb_mod_initialize(mrb_state *mrb, mrb_value mod)
 {
   mrb_value b;
@@ -1250,45 +1201,6 @@ mrb_mod_initialize(mrb_state *mrb, mrb_value mod)
   return mod;
 }
 
-mrb_value mrb_class_instance_method_list(mrb_state*, mrb_bool, struct RClass*, int);
-
-/* 15.2.2.4.33 */
-/*
- *  call-seq:
- *     mod.instance_methods(include_super=true)   -> array
- *
- *  Returns an array containing the names of the public and protected instance
- *  methods in the receiver. For a module, these are the public and protected methods;
- *  for a class, they are the instance (not singleton) methods. With no
- *  argument, or with an argument that is <code>false</code>, the
- *  instance methods in <i>mod</i> are returned, otherwise the methods
- *  in <i>mod</i> and <i>mod</i>'s superclasses are returned.
- *
- *     module A
- *       def method1()  end
- *     end
- *     class B
- *       def method2()  end
- *     end
- *     class C < B
- *       def method3()  end
- *     end
- *
- *     A.instance_methods                #=> [:method1]
- *     B.instance_methods(false)         #=> [:method2]
- *     C.instance_methods(false)         #=> [:method3]
- *     C.instance_methods(true).length   #=> 43
- */
-
-static mrb_value
-mrb_mod_instance_methods(mrb_state *mrb, mrb_value mod)
-{
-  struct RClass *c = mrb_class_ptr(mod);
-  mrb_bool recur = TRUE;
-  mrb_get_args(mrb, "|b", &recur);
-  return mrb_class_instance_method_list(mrb, recur, c, 0);
-}
-
 /* implementation of module_eval/class_eval */
 mrb_value mrb_mod_module_eval(mrb_state*, mrb_value);
 
@@ -1365,9 +1277,9 @@ mc_clear_by_class(mrb_state *mrb, struct RClass *c)
   struct mrb_cache_entry *mc = mrb->cache;
   int i;
 
-  if (c->flags & MRB_FLAG_IS_INHERITED) {
+  if (c->flags & MRB_FL_CLASS_IS_INHERITED) {
     mc_clear_all(mrb);
-    c->flags &= ~MRB_FLAG_IS_INHERITED;
+    c->flags &= ~MRB_FL_CLASS_IS_INHERITED;
     return;
   }
   for (i=0; i<MRB_METHOD_CACHE_SIZE; i++) {
@@ -1381,9 +1293,9 @@ mc_clear_by_id(mrb_state *mrb, struct RClass *c, mrb_sym mid)
   struct mrb_cache_entry *mc = mrb->cache;
   int i;
 
-  if (c->flags & MRB_FLAG_IS_INHERITED) {
+  if (c->flags & MRB_FL_CLASS_IS_INHERITED) {
     mc_clear_all(mrb);
-    c->flags &= ~MRB_FLAG_IS_INHERITED;
+    c->flags &= ~MRB_FL_CLASS_IS_INHERITED;
     return;
   }
   for (i=0; i<MRB_METHOD_CACHE_SIZE; i++) {
@@ -1480,7 +1392,7 @@ mrb_mod_attr_reader(mrb_state *mrb, mrb_value mod)
     mrb_str_cat_lit(mrb, str, "@");
     mrb_str_cat_str(mrb, str, name);
     sym = mrb_intern_str(mrb, str);
-    mrb_iv_check(mrb, sym);
+    mrb_iv_name_sym_check(mrb, sym);
     name = mrb_symbol_value(sym);
     p = mrb_proc_new_cfunc_with_env(mrb, attr_reader, 1, &name);
     MRB_METHOD_FROM_PROC(m, p);
@@ -1525,7 +1437,7 @@ mrb_mod_attr_writer(mrb_state *mrb, mrb_value mod)
     mrb_str_cat_lit(mrb, str, "@");
     mrb_str_cat_str(mrb, str, name);
     sym = mrb_intern_str(mrb, str);
-    mrb_iv_check(mrb, sym);
+    mrb_iv_name_sym_check(mrb, sym);
     attr = mrb_symbol_value(sym);
 
     /* prepare method name (name=) */
@@ -1572,29 +1484,20 @@ mrb_instance_alloc(mrb_state *mrb, mrb_value cv)
  *
  */
 
-MRB_API mrb_value
+mrb_value
 mrb_instance_new(mrb_state *mrb, mrb_value cv)
 {
   mrb_value obj, blk;
   mrb_value *argv;
   mrb_int argc;
   mrb_sym init;
-  mrb_method_t m;
 
   mrb_get_args(mrb, "*&", &argv, &argc, &blk);
   obj = mrb_instance_alloc(mrb, cv);
   init = mrb_intern_lit(mrb, "initialize");
-  m = mrb_method_search(mrb, mrb_class(mrb, obj), init);
-  if (MRB_METHOD_CFUNC_P(m)) {
-    mrb_func_t f = MRB_METHOD_CFUNC(m);
-    if (f != mrb_bob_init) {
-      f(mrb, obj);
-    }
-  }
-  else {
+  if (!mrb_func_basic_p(mrb, obj, init, mrb_bob_init)) {
     mrb_funcall_with_block(mrb, obj, init, argc, argv, blk);
   }
-
   return obj;
 }
 
@@ -1751,11 +1654,7 @@ mrb_class_path(mrb_state *mrb, struct RClass *c)
   }
   else if (mrb_symbol_p(path)) {
     /* toplevel class/module */
-    const char *str;
-    mrb_int len;
-
-    str = mrb_sym2name_len(mrb, mrb_symbol(path), &len);
-    return mrb_str_new(mrb, str, len);
+    return mrb_sym2str(mrb, mrb_symbol(path));
   }
   return mrb_str_dup(mrb, path);
 }
@@ -1763,10 +1662,10 @@ mrb_class_path(mrb_state *mrb, struct RClass *c)
 MRB_API struct RClass*
 mrb_class_real(struct RClass* cl)
 {
-  if (cl == 0)
-    return NULL;
+  if (cl == 0) return NULL;
   while ((cl->tt == MRB_TT_SCLASS) || (cl->tt == MRB_TT_ICLASS)) {
     cl = cl->super;
+    if (cl == 0) return NULL;
   }
   return cl;
 }
@@ -1774,13 +1673,8 @@ mrb_class_real(struct RClass* cl)
 MRB_API const char*
 mrb_class_name(mrb_state *mrb, struct RClass* c)
 {
-  mrb_value path = mrb_class_path(mrb, c);
-  if (mrb_nil_p(path)) {
-    path = mrb_str_new_lit(mrb, "#<Class:");
-    mrb_str_concat(mrb, path, mrb_ptr_to_str(mrb, c));
-    mrb_str_cat_lit(mrb, path, ">");
-  }
-  return RSTRING_PTR(path);
+  mrb_value name = class_name_str(mrb, c);
+  return RSTRING_PTR(name);
 }
 
 MRB_API const char*
@@ -1892,15 +1786,13 @@ mrb_define_alias(mrb_state *mrb, struct RClass *klass, const char *name1, const
  * show information on the thing we're attached to as well.
  */
 
-static mrb_value
+mrb_value
 mrb_mod_to_s(mrb_state *mrb, mrb_value klass)
 {
-  mrb_value str;
 
   if (mrb_type(klass) == MRB_TT_SCLASS) {
     mrb_value v = mrb_iv_get(mrb, klass, mrb_intern_lit(mrb, "__attached__"));
-
-    str = mrb_str_new_lit(mrb, "#<Class:");
+    mrb_value str = mrb_str_new_lit(mrb, "#<Class:");
 
     if (class_ptr_p(v)) {
       mrb_str_cat_str(mrb, str, mrb_inspect(mrb, v));
@@ -1911,34 +1803,7 @@ mrb_mod_to_s(mrb_state *mrb, mrb_value klass)
     return mrb_str_cat_lit(mrb, str, ">");
   }
   else {
-    struct RClass *c;
-    mrb_value path;
-
-    str = mrb_str_new_capa(mrb, 32);
-    c = mrb_class_ptr(klass);
-    path = mrb_class_path(mrb, c);
-
-    if (mrb_nil_p(path)) {
-      switch (mrb_type(klass)) {
-        case MRB_TT_CLASS:
-          mrb_str_cat_lit(mrb, str, "#<Class:");
-          break;
-
-        case MRB_TT_MODULE:
-          mrb_str_cat_lit(mrb, str, "#<Module:");
-          break;
-
-        default:
-          /* Shouldn't be happened? */
-          mrb_str_cat_lit(mrb, str, "#<??????:");
-          break;
-      }
-      mrb_str_concat(mrb, str, mrb_ptr_to_str(mrb, c));
-      return mrb_str_cat_lit(mrb, str, ">");
-    }
-    else {
-      return path;
-    }
+    return class_name_str(mrb, mrb_class_ptr(klass));
   }
 }
 
@@ -1950,11 +1815,11 @@ mrb_mod_alias(mrb_state *mrb, mrb_value mod)
 
   mrb_get_args(mrb, "nn", &new_name, &old_name);
   mrb_alias_method(mrb, c, new_name, old_name);
-  return mrb_nil_value();
+  return mod;
 }
 
-static void
-undef_method(mrb_state *mrb, struct RClass *c, mrb_sym a)
+void
+mrb_undef_method_id(mrb_state *mrb, struct RClass *c, mrb_sym a)
 {
   if (!mrb_obj_respond_to(mrb, c, a)) {
     mrb_name_error(mrb, a, "undefined method '%S' for class '%S'", mrb_sym2str(mrb, a), mrb_obj_value(c));
@@ -1970,7 +1835,7 @@ undef_method(mrb_state *mrb, struct RClass *c, mrb_sym a)
 MRB_API void
 mrb_undef_method(mrb_state *mrb, struct RClass *c, const char *name)
 {
-  undef_method(mrb, c, mrb_intern_cstr(mrb, name));
+  mrb_undef_method_id(mrb, c, mrb_intern_cstr(mrb, name));
 }
 
 MRB_API void
@@ -1988,297 +1853,20 @@ mrb_mod_undef(mrb_state *mrb, mrb_value mod)
 
   mrb_get_args(mrb, "*", &argv, &argc);
   while (argc--) {
-    undef_method(mrb, c, to_sym(mrb, *argv));
+    mrb_undef_method_id(mrb, c, to_sym(mrb, *argv));
     argv++;
   }
   return mrb_nil_value();
 }
 
-static mrb_value
-mod_define_method(mrb_state *mrb, mrb_value self)
-{
-  struct RClass *c = mrb_class_ptr(self);
-  struct RProc *p;
-  mrb_method_t m;
-  mrb_sym mid;
-  mrb_value proc = mrb_undef_value();
-  mrb_value blk;
-
-  mrb_get_args(mrb, "n|o&", &mid, &proc, &blk);
-  switch (mrb_type(proc)) {
-    case MRB_TT_PROC:
-      blk = proc;
-      break;
-    case MRB_TT_UNDEF:
-      /* ignored */
-      break;
-    default:
-      mrb_raisef(mrb, E_TYPE_ERROR, "wrong argument type %S (expected Proc)", mrb_obj_value(mrb_obj_class(mrb, proc)));
-      break;
-  }
-  if (mrb_nil_p(blk)) {
-    mrb_raise(mrb, E_ARGUMENT_ERROR, "no block given");
-  }
-  p = (struct RProc*)mrb_obj_alloc(mrb, MRB_TT_PROC, mrb->proc_class);
-  mrb_proc_copy(p, mrb_proc_ptr(blk));
-  p->flags |= MRB_PROC_STRICT;
-  MRB_METHOD_FROM_PROC(m, p);
-  mrb_define_method_raw(mrb, c, mid, m);
-  return mrb_symbol_value(mid);
-}
-
-static mrb_value
-top_define_method(mrb_state *mrb, mrb_value self)
-{
-  return mod_define_method(mrb, mrb_obj_value(mrb->object_class));
-}
-
-static void
-check_cv_name_str(mrb_state *mrb, mrb_value str)
-{
-  const char *s = RSTRING_PTR(str);
-  mrb_int len = RSTRING_LEN(str);
-
-  if (len < 3 || !(s[0] == '@' && s[1] == '@')) {
-    mrb_name_error(mrb, mrb_intern_str(mrb, str), "'%S' is not allowed as a class variable name", str);
-  }
-}
-
-static void
-check_cv_name_sym(mrb_state *mrb, mrb_sym id)
-{
-  check_cv_name_str(mrb, mrb_sym2str(mrb, id));
-}
-
-/* 15.2.2.4.16 */
-/*
- *  call-seq:
- *     obj.class_variable_defined?(symbol)    -> true or false
- *
- *  Returns <code>true</code> if the given class variable is defined
- *  in <i>obj</i>.
- *
- *     class Fred
- *       @@foo = 99
- *     end
- *     Fred.class_variable_defined?(:@@foo)    #=> true
- *     Fred.class_variable_defined?(:@@bar)    #=> false
- */
-
-static mrb_value
-mrb_mod_cvar_defined(mrb_state *mrb, mrb_value mod)
-{
-  mrb_sym id;
-
-  mrb_get_args(mrb, "n", &id);
-  check_cv_name_sym(mrb, id);
-  return mrb_bool_value(mrb_cv_defined(mrb, mod, id));
-}
-
-/* 15.2.2.4.17 */
-/*
- *  call-seq:
- *     mod.class_variable_get(symbol)    -> obj
- *
- *  Returns the value of the given class variable (or throws a
- *  <code>NameError</code> exception). The <code>@@</code> part of the
- *  variable name should be included for regular class variables
- *
- *     class Fred
- *       @@foo = 99
- *     end
- *     Fred.class_variable_get(:@@foo)     #=> 99
- */
-
-static mrb_value
-mrb_mod_cvar_get(mrb_state *mrb, mrb_value mod)
-{
-  mrb_sym id;
-
-  mrb_get_args(mrb, "n", &id);
-  check_cv_name_sym(mrb, id);
-  return mrb_cv_get(mrb, mod, id);
-}
-
-/* 15.2.2.4.18 */
-/*
- *  call-seq:
- *     obj.class_variable_set(symbol, obj)    -> obj
- *
- *  Sets the class variable names by <i>symbol</i> to
- *  <i>object</i>.
- *
- *     class Fred
- *       @@foo = 99
- *       def foo
- *         @@foo
- *       end
- *     end
- *     Fred.class_variable_set(:@@foo, 101)     #=> 101
- *     Fred.new.foo                             #=> 101
- */
-
-static mrb_value
-mrb_mod_cvar_set(mrb_state *mrb, mrb_value mod)
-{
-  mrb_value value;
-  mrb_sym id;
-
-  mrb_get_args(mrb, "no", &id, &value);
-  check_cv_name_sym(mrb, id);
-  mrb_cv_set(mrb, mod, id, value);
-  return value;
-}
-
-/* 15.2.2.4.39 */
-/*
- *  call-seq:
- *     remove_class_variable(sym)    -> obj
- *
- *  Removes the definition of the <i>sym</i>, returning that
- *  constant's value.
- *
- *     class Dummy
- *       @@var = 99
- *       puts @@var
- *       p class_variables
- *       remove_class_variable(:@@var)
- *       p class_variables
- *     end
- *
- *  <em>produces:</em>
- *
- *     99
- *     [:@@var]
- *     []
- */
-
-static mrb_value
-mrb_mod_remove_cvar(mrb_state *mrb, mrb_value mod)
-{
-  mrb_value val;
-  mrb_sym id;
-
-  mrb_get_args(mrb, "n", &id);
-  check_cv_name_sym(mrb, id);
-
-  val = mrb_iv_remove(mrb, mod, id);
-  if (!mrb_undef_p(val)) return val;
-
-  if (mrb_cv_defined(mrb, mod, id)) {
-    mrb_name_error(mrb, id, "cannot remove %S for %S",
-                   mrb_sym2str(mrb, id), mod);
-  }
-
-  mrb_name_error(mrb, id, "class variable %S not defined for %S",
-                 mrb_sym2str(mrb, id), mod);
-
- /* not reached */
- return mrb_nil_value();
-}
-
-/* 15.2.2.4.34 */
-/*
- *  call-seq:
- *     mod.method_defined?(symbol)    -> true or false
- *
- *  Returns +true+ if the named method is defined by
- *  _mod_ (or its included modules and, if _mod_ is a class,
- *  its ancestors). Public and protected methods are matched.
- *
- *     module A
- *       def method1()  end
- *     end
- *     class B
- *       def method2()  end
- *     end
- *     class C < B
- *       include A
- *       def method3()  end
- *     end
- *
- *     A.method_defined? :method1    #=> true
- *     C.method_defined? "method1"   #=> true
- *     C.method_defined? "method2"   #=> true
- *     C.method_defined? "method3"   #=> true
- *     C.method_defined? "method4"   #=> false
- */
-
-static mrb_value
-mrb_mod_method_defined(mrb_state *mrb, mrb_value mod)
-{
-  mrb_sym id;
-
-  mrb_get_args(mrb, "n", &id);
-  return mrb_bool_value(mrb_obj_respond_to(mrb, mrb_class_ptr(mod), id));
-}
-
-static void
-remove_method(mrb_state *mrb, mrb_value mod, mrb_sym mid)
-{
-  struct RClass *c = mrb_class_ptr(mod);
-  khash_t(mt) *h = find_origin(c)->mt;
-  khiter_t k;
-
-  if (h) {
-    k = kh_get(mt, mrb, h, mid);
-    if (k != kh_end(h)) {
-      kh_del(mt, mrb, h, k);
-      mrb_funcall(mrb, mod, "method_removed", 1, mrb_symbol_value(mid));
-      return;
-    }
-  }
-
-  mrb_name_error(mrb, mid, "method '%S' not defined in %S",
-    mrb_sym2str(mrb, mid), mod);
-}
-
-/* 15.2.2.4.41 */
-/*
- *  call-seq:
- *     remove_method(symbol)   -> self
- *
- *  Removes the method identified by _symbol_ from the current
- *  class. For an example, see <code>Module.undef_method</code>.
- */
-
-static mrb_value
-mrb_mod_remove_method(mrb_state *mrb, mrb_value mod)
-{
-  mrb_int argc;
-  mrb_value *argv;
-
-  mrb_get_args(mrb, "*", &argv, &argc);
-  while (argc--) {
-    remove_method(mrb, mod, to_sym(mrb, *argv));
-    argv++;
-  }
-  return mod;
-}
-
-
-
-static void
-check_const_name_str(mrb_state *mrb, mrb_value str)
-{
-  if (RSTRING_LEN(str) < 1 || !ISUPPER(*RSTRING_PTR(str))) {
-    mrb_name_error(mrb, mrb_intern_str(mrb, str), "wrong constant name %S", str);
-  }
-}
-
 static void
 check_const_name_sym(mrb_state *mrb, mrb_sym id)
 {
-  check_const_name_str(mrb, mrb_sym2str(mrb, id));
-}
-
-static mrb_value
-const_defined(mrb_state *mrb, mrb_value mod, mrb_sym id, mrb_bool inherit)
-{
-  if (inherit) {
-    return mrb_bool_value(mrb_const_defined(mrb, mod, id));
+  mrb_int len;
+  const char *name = mrb_sym2name_len(mrb, id, &len);
+  if (!mrb_const_name_p(mrb, name, len)) {
+    mrb_name_error(mrb, id, "wrong constant name %S", mrb_sym2str(mrb, id));
   }
-  return mrb_bool_value(mrb_const_defined_at(mrb, mod, id));
 }
 
 static mrb_value
@@ -2289,7 +1877,10 @@ mrb_mod_const_defined(mrb_state *mrb, mrb_value mod)
 
   mrb_get_args(mrb, "n|b", &id, &inherit);
   check_const_name_sym(mrb, id);
-  return const_defined(mrb, mod, id, inherit);
+  if (inherit) {
+    return mrb_bool_value(mrb_const_defined(mrb, mod, id));
+  }
+  return mrb_bool_value(mrb_const_defined_at(mrb, mod, id));
 }
 
 static mrb_value
@@ -2316,7 +1907,7 @@ mrb_mod_const_get(mrb_state *mrb, mrb_value mod)
   }
 
   /* const get with class path string */
-  path = mrb_string_type(mrb, path);
+  path = mrb_ensure_string_type(mrb, path);
   ptr = RSTRING_PTR(path);
   len = RSTRING_LEN(path);
   off = 0;
@@ -2326,7 +1917,14 @@ mrb_mod_const_get(mrb_state *mrb, mrb_value mod)
     end = (end == -1) ? len : end;
     id = mrb_intern(mrb, ptr+off, end-off);
     mod = mrb_const_get_sym(mrb, mod, id);
-    off = (end == len) ? end : end+2;
+    if (end == len)
+      off = end;
+    else {
+      off = end + 2;
+      if (off == len) {         /* trailing "::" */
+        mrb_name_error(mrb, id, "wrong constant name '%S'", path);
+      }
+    }
   }
 
   return mod;
@@ -2379,11 +1977,79 @@ mrb_mod_const_missing(mrb_state *mrb, mrb_value mod)
   return mrb_nil_value();
 }
 
+/* 15.2.2.4.34 */
+/*
+ *  call-seq:
+ *     mod.method_defined?(symbol)    -> true or false
+ *
+ *  Returns +true+ if the named method is defined by
+ *  _mod_ (or its included modules and, if _mod_ is a class,
+ *  its ancestors). Public and protected methods are matched.
+ *
+ *     module A
+ *       def method1()  end
+ *     end
+ *     class B
+ *       def method2()  end
+ *     end
+ *     class C < B
+ *       include A
+ *       def method3()  end
+ *     end
+ *
+ *     A.method_defined? :method1    #=> true
+ *     C.method_defined? "method1"   #=> true
+ *     C.method_defined? "method2"   #=> true
+ *     C.method_defined? "method3"   #=> true
+ *     C.method_defined? "method4"   #=> false
+ */
+
+static mrb_value
+mrb_mod_method_defined(mrb_state *mrb, mrb_value mod)
+{
+  mrb_sym id;
+
+  mrb_get_args(mrb, "n", &id);
+  return mrb_bool_value(mrb_obj_respond_to(mrb, mrb_class_ptr(mod), id));
+}
+
+static mrb_value
+mod_define_method(mrb_state *mrb, mrb_value self)
+{
+  struct RClass *c = mrb_class_ptr(self);
+  struct RProc *p;
+  mrb_method_t m;
+  mrb_sym mid;
+  mrb_value proc = mrb_undef_value();
+  mrb_value blk;
+
+  mrb_get_args(mrb, "n|o&", &mid, &proc, &blk);
+  switch (mrb_type(proc)) {
+    case MRB_TT_PROC:
+      blk = proc;
+      break;
+    case MRB_TT_UNDEF:
+      /* ignored */
+      break;
+    default:
+      mrb_raisef(mrb, E_TYPE_ERROR, "wrong argument type %S (expected Proc)", mrb_obj_value(mrb_obj_class(mrb, proc)));
+      break;
+  }
+  if (mrb_nil_p(blk)) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "no block given");
+  }
+  p = (struct RProc*)mrb_obj_alloc(mrb, MRB_TT_PROC, mrb->proc_class);
+  mrb_proc_copy(p, mrb_proc_ptr(blk));
+  p->flags |= MRB_PROC_STRICT;
+  MRB_METHOD_FROM_PROC(m, p);
+  mrb_define_method_raw(mrb, c, mid, m);
+  return mrb_symbol_value(mid);
+}
+
 static mrb_value
-mrb_mod_s_constants(mrb_state *mrb, mrb_value mod)
+top_define_method(mrb_state *mrb, mrb_value self)
 {
-  mrb_raise(mrb, E_NOTIMP_ERROR, "Module.constants not implemented");
-  return mrb_nil_value();       /* not reached */
+  return mod_define_method(mrb, mrb_obj_value(mrb->object_class));
 }
 
 static mrb_value
@@ -2398,7 +2064,7 @@ mrb_mod_eqq(mrb_state *mrb, mrb_value mod)
   return mrb_bool_value(eqq);
 }
 
-MRB_API mrb_value
+static mrb_value
 mrb_mod_module_function(mrb_state *mrb, mrb_value mod)
 {
   mrb_value *argv;
@@ -2439,8 +2105,6 @@ mrb_mod_module_function(mrb_state *mrb, mrb_value mod)
 mrb_value mrb_obj_id_m(mrb_state *mrb, mrb_value self);
 /* implementation of instance_eval */
 mrb_value mrb_obj_instance_eval(mrb_state*, mrb_value);
-/* implementation of Module.nesting */
-mrb_value mrb_mod_s_nesting(mrb_state*, mrb_value);
 
 static mrb_value
 inspect_main(mrb_state *mrb, mrb_value mod)
@@ -2489,8 +2153,9 @@ mrb_init_class(mrb_state *mrb)
   mrb_define_method(mrb, bob, "!",                       mrb_bob_not,              MRB_ARGS_NONE());
   mrb_define_method(mrb, bob, "==",                      mrb_obj_equal_m,          MRB_ARGS_REQ(1)); /* 15.3.1.3.1  */
   mrb_define_method(mrb, bob, "!=",                      mrb_obj_not_equal_m,      MRB_ARGS_REQ(1));
-  mrb_define_method(mrb, bob, "__id__",                  mrb_obj_id_m,             MRB_ARGS_NONE()); /* 15.3.1.3.3  */
-  mrb_define_method(mrb, bob, "__send__",                mrb_f_send,               MRB_ARGS_ANY());  /* 15.3.1.3.4  */
+  mrb_define_method(mrb, bob, "__id__",                  mrb_obj_id_m,             MRB_ARGS_NONE()); /* 15.3.1.3.4  */
+  mrb_define_method(mrb, bob, "__send__",                mrb_f_send,               MRB_ARGS_ANY());  /* 15.3.1.3.5  */
+  mrb_define_method(mrb, bob, "equal?",                  mrb_obj_equal_m,          MRB_ARGS_REQ(1)); /* 15.3.1.3.11 */
   mrb_define_method(mrb, bob, "instance_eval",           mrb_obj_instance_eval,    MRB_ARGS_ANY());  /* 15.3.1.3.18 */
 
   mrb_define_class_method(mrb, cls, "new",               mrb_class_new_class,      MRB_ARGS_OPT(1));
@@ -2500,9 +2165,6 @@ mrb_init_class(mrb_state *mrb)
   mrb_define_method(mrb, cls, "inherited",               mrb_bob_init,             MRB_ARGS_REQ(1));
 
   MRB_SET_INSTANCE_TT(mod, MRB_TT_MODULE);
-  mrb_define_method(mrb, mod, "class_variable_defined?", mrb_mod_cvar_defined,     MRB_ARGS_REQ(1)); /* 15.2.2.4.16 */
-  mrb_define_method(mrb, mod, "class_variable_get",      mrb_mod_cvar_get,         MRB_ARGS_REQ(1)); /* 15.2.2.4.17 */
-  mrb_define_method(mrb, mod, "class_variable_set",      mrb_mod_cvar_set,         MRB_ARGS_REQ(2)); /* 15.2.2.4.18 */
   mrb_define_method(mrb, mod, "extend_object",           mrb_mod_extend_object,    MRB_ARGS_REQ(1)); /* 15.2.2.4.25 */
   mrb_define_method(mrb, mod, "extended",                mrb_bob_init,             MRB_ARGS_REQ(1)); /* 15.2.2.4.26 */
   mrb_define_method(mrb, mod, "prepended",               mrb_bob_init,             MRB_ARGS_REQ(1));
@@ -2511,18 +2173,12 @@ mrb_init_class(mrb_state *mrb)
   mrb_define_method(mrb, mod, "append_features",         mrb_mod_append_features,  MRB_ARGS_REQ(1)); /* 15.2.2.4.10 */
   mrb_define_method(mrb, mod, "class_eval",              mrb_mod_module_eval,      MRB_ARGS_ANY());  /* 15.2.2.4.15 */
   mrb_define_method(mrb, mod, "included",                mrb_bob_init,             MRB_ARGS_REQ(1)); /* 15.2.2.4.29 */
-  mrb_define_method(mrb, mod, "included_modules",        mrb_mod_included_modules, MRB_ARGS_NONE()); /* 15.2.2.4.30 */
   mrb_define_method(mrb, mod, "initialize",              mrb_mod_initialize,       MRB_ARGS_NONE()); /* 15.2.2.4.31 */
-  mrb_define_method(mrb, mod, "instance_methods",        mrb_mod_instance_methods, MRB_ARGS_ANY());  /* 15.2.2.4.33 */
-  mrb_define_method(mrb, mod, "method_defined?",         mrb_mod_method_defined,   MRB_ARGS_REQ(1)); /* 15.2.2.4.34 */
   mrb_define_method(mrb, mod, "module_eval",             mrb_mod_module_eval,      MRB_ARGS_ANY());  /* 15.2.2.4.35 */
   mrb_define_method(mrb, mod, "module_function",         mrb_mod_module_function,  MRB_ARGS_ANY());
   mrb_define_method(mrb, mod, "private",                 mrb_mod_dummy_visibility, MRB_ARGS_ANY());  /* 15.2.2.4.36 */
   mrb_define_method(mrb, mod, "protected",               mrb_mod_dummy_visibility, MRB_ARGS_ANY());  /* 15.2.2.4.37 */
   mrb_define_method(mrb, mod, "public",                  mrb_mod_dummy_visibility, MRB_ARGS_ANY());  /* 15.2.2.4.38 */
-  mrb_define_method(mrb, mod, "remove_class_variable",   mrb_mod_remove_cvar,      MRB_ARGS_REQ(1)); /* 15.2.2.4.39 */
-  mrb_define_method(mrb, mod, "remove_method",           mrb_mod_remove_method,    MRB_ARGS_ANY());  /* 15.2.2.4.41 */
-  mrb_define_method(mrb, mod, "method_removed",          mrb_bob_init,             MRB_ARGS_REQ(1));
   mrb_define_method(mrb, mod, "attr_reader",             mrb_mod_attr_reader,      MRB_ARGS_ANY());  /* 15.2.2.4.13 */
   mrb_define_method(mrb, mod, "attr_writer",             mrb_mod_attr_writer,      MRB_ARGS_ANY());  /* 15.2.2.4.14 */
   mrb_define_method(mrb, mod, "to_s",                    mrb_mod_to_s,             MRB_ARGS_NONE());
@@ -2533,14 +2189,11 @@ mrb_init_class(mrb_state *mrb)
   mrb_define_method(mrb, mod, "const_defined?",          mrb_mod_const_defined,    MRB_ARGS_ARG(1,1)); /* 15.2.2.4.20 */
   mrb_define_method(mrb, mod, "const_get",               mrb_mod_const_get,        MRB_ARGS_REQ(1)); /* 15.2.2.4.21 */
   mrb_define_method(mrb, mod, "const_set",               mrb_mod_const_set,        MRB_ARGS_REQ(2)); /* 15.2.2.4.23 */
-  mrb_define_method(mrb, mod, "constants",               mrb_mod_constants,        MRB_ARGS_OPT(1)); /* 15.2.2.4.24 */
   mrb_define_method(mrb, mod, "remove_const",            mrb_mod_remove_const,     MRB_ARGS_REQ(1)); /* 15.2.2.4.40 */
   mrb_define_method(mrb, mod, "const_missing",           mrb_mod_const_missing,    MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, mod, "method_defined?",         mrb_mod_method_defined,   MRB_ARGS_REQ(1)); /* 15.2.2.4.34 */
   mrb_define_method(mrb, mod, "define_method",           mod_define_method,        MRB_ARGS_ARG(1,1));
-  mrb_define_method(mrb, mod, "class_variables",         mrb_mod_class_variables,  MRB_ARGS_NONE()); /* 15.2.2.4.19 */
-  mrb_define_method(mrb, mod, "===",                     mrb_mod_eqq,              MRB_ARGS_REQ(1));
-  mrb_define_class_method(mrb, mod, "constants",         mrb_mod_s_constants,      MRB_ARGS_ANY());  /* 15.2.2.3.1 */
-  mrb_define_class_method(mrb, mod, "nesting",           mrb_mod_s_nesting,        MRB_ARGS_REQ(0)); /* 15.2.2.3.2 */
+  mrb_define_method(mrb, mod, "===",                     mrb_mod_eqq,              MRB_ARGS_REQ(1)); /* 15.2.2.4.7 */
 
   mrb_undef_method(mrb, cls, "append_features");
   mrb_undef_method(mrb, cls, "extend_object");
diff --git a/src/codedump.c b/src/codedump.c
index d79a65a70..12d609075 100644
--- a/src/codedump.c
+++ b/src/codedump.c
@@ -6,457 +6,526 @@
 #include <mruby/proc.h>
 
 #ifndef MRB_DISABLE_STDIO
-static int
-print_r(mrb_state *mrb, mrb_irep *irep, size_t n, int pre)
+static void
+print_r(mrb_state *mrb, mrb_irep *irep, size_t n)
 {
   size_t i;
 
-  if (n == 0) return 0;
+  if (n == 0) return;
 
   for (i=0; i+1<irep->nlocals; i++) {
     if (irep->lv[i].r == n) {
       mrb_sym sym = irep->lv[i].name;
-      if (pre) printf(" ");
-      printf("R%d:%s", (int)n, mrb_sym2name(mrb, sym));
-      return 1;
+      printf(" R%d:%s", (int)n, mrb_sym2name(mrb, sym));
+      break;
     }
   }
-  return 0;
 }
 
-#define RA  1
-#define RB  2
-#define RAB 3
-
 static void
-print_lv(mrb_state *mrb, mrb_irep *irep, mrb_code c, int r)
+print_lv_a(mrb_state *mrb, mrb_irep *irep, uint16_t a)
 {
-  int pre = 0;
+  if (!irep->lv || a >= irep->nlocals || a == 0) {
+    printf("\n");
+    return;
+  }
+  printf("\t;");
+  print_r(mrb, irep, a);
+  printf("\n");
+}
 
-  if (!irep->lv
-      || ((!(r & RA) || GETARG_A(c) >= irep->nlocals)
-       && (!(r & RB) || GETARG_B(c) >= irep->nlocals))) {
+static void
+print_lv_ab(mrb_state *mrb, mrb_irep *irep, uint16_t a, uint16_t b)
+{
+  if (!irep->lv || (a >= irep->nlocals && b >= irep->nlocals) || a+b == 0) {
     printf("\n");
     return;
   }
-  printf("\t; ");
-  if (r & RA) {
-    pre = print_r(mrb, irep, GETARG_A(c), 0);
+  printf("\t;");
+  if (a > 0) print_r(mrb, irep, a);
+  if (b > 0) print_r(mrb, irep, b);
+  printf("\n");
+}
+
+static void
+print_header(mrb_state *mrb, mrb_irep *irep, ptrdiff_t i)
+{
+  int32_t line;
+
+  line = mrb_debug_get_line(mrb, irep, i);
+  if (line < 0) {
+    printf("      ");
   }
-  if (r & RB) {
-    print_r(mrb, irep, GETARG_B(c), pre);
+  else {
+    printf("%5d ", line);
   }
-  printf("\n");
+
+  printf("%03d ", (int)i);
 }
-#endif
+
+#define CASE(insn,ops) case insn: FETCH_ ## ops (); L_ ## insn
 
 static void
 codedump(mrb_state *mrb, mrb_irep *irep)
 {
-#ifndef MRB_DISABLE_STDIO
-  int i;
   int ai;
-  mrb_code c;
+  mrb_code *pc, *pcend;
+  mrb_code ins;
   const char *file = NULL, *next_file;
-  int32_t line;
 
   if (!irep) return;
-  printf("irep %p nregs=%d nlocals=%d pools=%d syms=%d reps=%d\n", (void*)irep,
-         irep->nregs, irep->nlocals, (int)irep->plen, (int)irep->slen, (int)irep->rlen);
+  printf("irep %p nregs=%d nlocals=%d pools=%d syms=%d reps=%d iseq=%d\n", (void*)irep,
+         irep->nregs, irep->nlocals, (int)irep->plen, (int)irep->slen, (int)irep->rlen, (int)irep->ilen);
+
+  if (irep->lv) {
+    int i;
+
+    printf("local variable names:\n");
+    for (i = 1; i < irep->nlocals; ++i) {
+      char const *s = mrb_sym2name(mrb, irep->lv[i - 1].name);
+      int n = irep->lv[i - 1].r ? irep->lv[i - 1].r : i;
+      printf("  R%d:%s\n", n, s ? s : "");
+    }
+  }
+
+  pc = irep->iseq;
+  pcend = pc + irep->ilen;
+  while (pc < pcend) {
+    ptrdiff_t i;
+    uint32_t a;
+    uint16_t b;
+    uint8_t c;
 
-  for (i = 0; i < (int)irep->ilen; i++) {
     ai = mrb_gc_arena_save(mrb);
 
-    next_file = mrb_debug_get_filename(irep, i);
+    i = pc - irep->iseq;
+    next_file = mrb_debug_get_filename(mrb, irep, i);
     if (next_file && file != next_file) {
       printf("file: %s\n", next_file);
       file = next_file;
     }
-    line = mrb_debug_get_line(irep, i);
-    if (line < 0) {
-      printf("      ");
-    }
-    else {
-      printf("%5d ", line);
-    }
-
-    printf("%03d ", i);
-    c = irep->iseq[i];
-    switch (GET_OPCODE(c)) {
-    case OP_NOP:
+    print_header(mrb, irep, i);
+    ins = READ_B();
+    switch (ins) {
+    CASE(OP_NOP, Z):
       printf("OP_NOP\n");
       break;
-    case OP_MOVE:
-      printf("OP_MOVE\tR%d\tR%d\t", GETARG_A(c), GETARG_B(c));
-      print_lv(mrb, irep, c, RAB);
+    CASE(OP_MOVE, BB):
+      printf("OP_MOVE\tR%d\tR%d\t", a, b);
+      print_lv_ab(mrb, irep, a, b);
       break;
-    case OP_LOADL:
+    CASE(OP_LOADL, BB):
       {
-        mrb_value v = irep->pool[GETARG_Bx(c)];
+        mrb_value v = irep->pool[b];
         mrb_value s = mrb_inspect(mrb, v);
-        printf("OP_LOADL\tR%d\tL(%d)\t; %s", GETARG_A(c), GETARG_Bx(c), RSTRING_PTR(s));
+        printf("OP_LOADL\tR%d\tL(%d)\t; %s", a, b, RSTRING_PTR(s));
       }
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_LOADI:
-      printf("OP_LOADI\tR%d\t%d\t", GETARG_A(c), GETARG_sBx(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_LOADSYM:
-      printf("OP_LOADSYM\tR%d\t:%s", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_Bx(c)]));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_LOADNIL:
-      printf("OP_LOADNIL\tR%d\t\t", GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_LOADSELF:
-      printf("OP_LOADSELF\tR%d\t\t", GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_LOADT:
-      printf("OP_LOADT\tR%d\t\t", GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_LOADF:
-      printf("OP_LOADF\tR%d\t\t", GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_GETGLOBAL:
-      printf("OP_GETGLOBAL\tR%d\t:%s", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_Bx(c)]));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_SETGLOBAL:
-      printf("OP_SETGLOBAL\t:%s\tR%d\t",
-             mrb_sym2name(mrb, irep->syms[GETARG_Bx(c)]),
-             GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_GETCONST:
-      printf("OP_GETCONST\tR%d\t:%s", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_Bx(c)]));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_SETCONST:
-      printf("OP_SETCONST\t:%s\tR%d\t",
-             mrb_sym2name(mrb, irep->syms[GETARG_Bx(c)]),
-             GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_GETMCNST:
-      printf("OP_GETMCNST\tR%d\tR%d::%s", GETARG_A(c), GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_Bx(c)]));
-      print_lv(mrb, irep, c, RAB);
-      break;
-    case OP_SETMCNST:
-      printf("OP_SETMCNST\tR%d::%s\tR%d", GETARG_A(c)+1,
-             mrb_sym2name(mrb, irep->syms[GETARG_Bx(c)]),
-             GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_GETIV:
-      printf("OP_GETIV\tR%d\t%s", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_Bx(c)]));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_SETIV:
-      printf("OP_SETIV\t%s\tR%d",
-             mrb_sym2name(mrb, irep->syms[GETARG_Bx(c)]),
-             GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_GETUPVAR:
-      printf("OP_GETUPVAR\tR%d\t%d\t%d",
-             GETARG_A(c), GETARG_B(c), GETARG_C(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_SETUPVAR:
-      printf("OP_SETUPVAR\tR%d\t%d\t%d",
-             GETARG_A(c), GETARG_B(c), GETARG_C(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_GETCV:
-      printf("OP_GETCV\tR%d\t%s", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_Bx(c)]));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_SETCV:
-      printf("OP_SETCV\t%s\tR%d",
-             mrb_sym2name(mrb, irep->syms[GETARG_Bx(c)]),
-             GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
-      break;
-    case OP_JMP:
-      printf("OP_JMP\t%03d (%d)\n", i+GETARG_sBx(c), GETARG_sBx(c));
-      break;
-    case OP_JMPIF:
-      printf("OP_JMPIF\tR%d\t%03d (%d)\n", GETARG_A(c), i+GETARG_sBx(c), GETARG_sBx(c));
-      break;
-    case OP_JMPNOT:
-      printf("OP_JMPNOT\tR%d\t%03d (%d)\n", GETARG_A(c), i+GETARG_sBx(c), GETARG_sBx(c));
-      break;
-    case OP_SEND:
-      printf("OP_SEND\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_SENDB:
-      printf("OP_SENDB\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_CALL:
-      printf("OP_CALL\tR%d\n", GETARG_A(c));
-      break;
-    case OP_TAILCALL:
-      printf("OP_TAILCALL\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_SUPER:
-      printf("OP_SUPER\tR%d\t%d\n", GETARG_A(c),
-             GETARG_C(c));
-      break;
-    case OP_ARGARY:
-      printf("OP_ARGARY\tR%d\t%d:%d:%d:%d", GETARG_A(c),
-             (GETARG_Bx(c)>>10)&0x3f,
-             (GETARG_Bx(c)>>9)&0x1,
-             (GETARG_Bx(c)>>4)&0x1f,
-             (GETARG_Bx(c)>>0)&0xf);
-      print_lv(mrb, irep, c, RA);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_LOADI, BB):
+      printf("OP_LOADI\tR%d\t%d\t", a, b);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_LOADINEG, BB):
+      printf("OP_LOADI\tR%d\t-%d\t", a, b);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_LOADI__1, B):
+      printf("OP_LOADI__1\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_LOADI_0, B): goto L_LOADI;
+    CASE(OP_LOADI_1, B): goto L_LOADI;
+    CASE(OP_LOADI_2, B): goto L_LOADI;
+    CASE(OP_LOADI_3, B): goto L_LOADI;
+    CASE(OP_LOADI_4, B): goto L_LOADI;
+    CASE(OP_LOADI_5, B): goto L_LOADI;
+    CASE(OP_LOADI_6, B): goto L_LOADI;
+    CASE(OP_LOADI_7, B):
+    L_LOADI:
+      printf("OP_LOADI_%d\tR%d\t\t", ins-(int)OP_LOADI_0, a);
+      print_lv_a(mrb, irep, a);
       break;
-
-    case OP_ENTER:
+    CASE(OP_LOADSYM, BB):
+      printf("OP_LOADSYM\tR%d\t:%s\t", a, mrb_sym2name(mrb, irep->syms[b]));
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_LOADNIL, B):
+      printf("OP_LOADNIL\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_LOADSELF, B):
+      printf("OP_LOADSELF\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_LOADT, B):
+      printf("OP_LOADT\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_LOADF, B):
+      printf("OP_LOADF\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_GETGV, BB):
+      printf("OP_GETGV\tR%d\t:%s", a, mrb_sym2name(mrb, irep->syms[b]));
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_SETGV, BB):
+      printf("OP_SETGV\t:%s\tR%d", mrb_sym2name(mrb, irep->syms[b]), a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_GETSV, BB):
+      printf("OP_GETSV\tR%d\t:%s", a, mrb_sym2name(mrb, irep->syms[b]));
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_SETSV, BB):
+      printf("OP_SETSV\t:%s\tR%d", mrb_sym2name(mrb, irep->syms[b]), a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_GETCONST, BB):
+      printf("OP_GETCONST\tR%d\t:%s", a, mrb_sym2name(mrb, irep->syms[b]));
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_SETCONST, BB):
+      printf("OP_SETCONST\t:%s\tR%d", mrb_sym2name(mrb, irep->syms[b]), a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_GETMCNST, BB):
+      printf("OP_GETMCNST\tR%d\tR%d::%s", a, a, mrb_sym2name(mrb, irep->syms[b]));
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_SETMCNST, BB):
+      printf("OP_SETMCNST\tR%d::%s\tR%d", a+1, mrb_sym2name(mrb, irep->syms[b]), a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_GETIV, BB):
+      printf("OP_GETIV\tR%d\t%s", a, mrb_sym2name(mrb, irep->syms[b]));
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_SETIV, BB):
+      printf("OP_SETIV\t%s\tR%d", mrb_sym2name(mrb, irep->syms[b]), a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_GETUPVAR, BBB):
+      printf("OP_GETUPVAR\tR%d\t%d\t%d", a, b, c);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_SETUPVAR, BBB):
+      printf("OP_SETUPVAR\tR%d\t%d\t%d", a, b, c);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_GETCV, BB):
+      printf("OP_GETCV\tR%d\t%s", a, mrb_sym2name(mrb, irep->syms[b]));
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_SETCV, BB):
+      printf("OP_SETCV\t%s\tR%d", mrb_sym2name(mrb, irep->syms[b]), a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_JMP, S):
+      printf("OP_JMP\t\t%03d\n", a);
+      break;
+    CASE(OP_JMPIF, BS):
+      printf("OP_JMPIF\tR%d\t%03d\t", a, b);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_JMPNOT, BS):
+      printf("OP_JMPNOT\tR%d\t%03d\t", a, b);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_JMPNIL, BS):
+      printf("OP_JMPNIL\tR%d\t%03d\t", a, b);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_SENDV, BB):
+      printf("OP_SENDV\tR%d\t:%s\n", a, mrb_sym2name(mrb, irep->syms[b]));
+      break;
+    CASE(OP_SENDVB, BB):
+      printf("OP_SENDVB\tR%d\t:%s\n", a, mrb_sym2name(mrb, irep->syms[b]));
+      break;
+    CASE(OP_SEND, BBB):
+      printf("OP_SEND\tR%d\t:%s\t%d\n", a, mrb_sym2name(mrb, irep->syms[b]), c);
+      break;
+    CASE(OP_SENDB, BBB):
+      printf("OP_SENDB\tR%d\t:%s\t%d\n", a, mrb_sym2name(mrb, irep->syms[b]), c);
+      break;
+    CASE(OP_CALL, Z):
+      printf("OP_CALL\n");
+      break;
+    CASE(OP_SUPER, BB):
+      printf("OP_SUPER\tR%d\t%d\n", a, b);
+      break;
+    CASE(OP_ARGARY, BS):
+      printf("OP_ARGARY\tR%d\t%d:%d:%d:%d (%d)", a,
+             (b>>11)&0x3f,
+             (b>>10)&0x1,
+             (b>>5)&0x1f,
+             (b>>4)&0x1,
+             (b>>0)&0xf);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_ENTER, W):
       printf("OP_ENTER\t%d:%d:%d:%d:%d:%d:%d\n",
-             (GETARG_Ax(c)>>18)&0x1f,
-             (GETARG_Ax(c)>>13)&0x1f,
-             (GETARG_Ax(c)>>12)&0x1,
-             (GETARG_Ax(c)>>7)&0x1f,
-             (GETARG_Ax(c)>>2)&0x1f,
-             (GETARG_Ax(c)>>1)&0x1,
-             GETARG_Ax(c) & 0x1);
-      break;
-    case OP_RETURN:
-      printf("OP_RETURN\tR%d", GETARG_A(c));
-      switch (GETARG_B(c)) {
-      case OP_R_NORMAL:
-        printf("\tnormal\t"); break;
-      case OP_R_RETURN:
-        printf("\treturn\t"); break;
-      case OP_R_BREAK:
-        printf("\tbreak\t"); break;
-      default:
-        printf("\tbroken\t"); break;
-      }
-      print_lv(mrb, irep, c, RA);
+             MRB_ASPEC_REQ(a),
+             MRB_ASPEC_OPT(a),
+             MRB_ASPEC_REST(a),
+             MRB_ASPEC_POST(a),
+             MRB_ASPEC_KEY(a),
+             MRB_ASPEC_KDICT(a),
+             MRB_ASPEC_BLOCK(a));
       break;
-    case OP_BLKPUSH:
-      printf("OP_BLKPUSH\tR%d\t%d:%d:%d:%d", GETARG_A(c),
-             (GETARG_Bx(c)>>10)&0x3f,
-             (GETARG_Bx(c)>>9)&0x1,
-             (GETARG_Bx(c)>>4)&0x1f,
-             (GETARG_Bx(c)>>0)&0xf);
-      print_lv(mrb, irep, c, RA);
+    CASE(OP_KEY_P, BB):
+      printf("OP_KEY_P\tR%d\t:%s\t", a, mrb_sym2name(mrb, irep->syms[b]));
+      print_lv_a(mrb, irep, a);
       break;
-
-    case OP_LAMBDA:
-      printf("OP_LAMBDA\tR%d\tI(%+d)\t", GETARG_A(c), GETARG_b(c)+1);
-      switch (GETARG_c(c)) {
-      case OP_L_METHOD:
-        printf("method"); break;
-      case OP_L_BLOCK:
-        printf("block"); break;
-      case OP_L_LAMBDA:
-        printf("lambda"); break;
-      }
-      print_lv(mrb, irep, c, RA);
+    CASE(OP_KEYEND, Z):
+      printf("OP_KEYEND\n");
       break;
-    case OP_RANGE:
-      printf("OP_RANGE\tR%d\tR%d\t%d", GETARG_A(c), GETARG_B(c), GETARG_C(c));
-      print_lv(mrb, irep, c, RAB);
+    CASE(OP_KARG, BB):
+      printf("OP_KARG\tR%d\t:%s\t", a, mrb_sym2name(mrb, irep->syms[b]));
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_METHOD:
-      printf("OP_METHOD\tR%d\t:%s", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]));
-      print_lv(mrb, irep, c, RA);
+    CASE(OP_RETURN, B):
+      printf("OP_RETURN\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
       break;
-
-    case OP_ADD:
-      printf("OP_ADD\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_ADDI:
-      printf("OP_ADDI\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_SUB:
-      printf("OP_SUB\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_SUBI:
-      printf("OP_SUBI\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_MUL:
-      printf("OP_MUL\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_DIV:
-      printf("OP_DIV\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_LT:
-      printf("OP_LT\t\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_LE:
-      printf("OP_LE\t\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_GT:
-      printf("OP_GT\t\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_GE:
-      printf("OP_GE\t\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
-      break;
-    case OP_EQ:
-      printf("OP_EQ\t\tR%d\t:%s\t%d\n", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]),
-             GETARG_C(c));
+    CASE(OP_RETURN_BLK, B):
+      printf("OP_RETURN_BLK\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
       break;
-
-    case OP_STOP:
-      printf("OP_STOP\n");
+    CASE(OP_BREAK, B):
+      printf("OP_BREAK\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
       break;
-
-    case OP_ARRAY:
-      printf("OP_ARRAY\tR%d\tR%d\t%d", GETARG_A(c), GETARG_B(c), GETARG_C(c));
-      print_lv(mrb, irep, c, RAB);
+    CASE(OP_BLKPUSH, BS):
+      printf("OP_BLKPUSH\tR%d\t%d:%d:%d:%d (%d)", a,
+             (b>>11)&0x3f,
+             (b>>10)&0x1,
+             (b>>5)&0x1f,
+             (b>>4)&0x1,
+             (b>>0)&0xf);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_LAMBDA, BB):
+      printf("OP_LAMBDA\tR%d\tI(%d:%p)\n", a, b, irep->reps[b]);
+      break;
+    CASE(OP_BLOCK, BB):
+      printf("OP_BLOCK\tR%d\tI(%d:%p)\n", a, b, irep->reps[b]);
+      break;
+    CASE(OP_METHOD, BB):
+      printf("OP_METHOD\tR%d\tI(%d:%p)\n", a, b, irep->reps[b]);
+      break;
+    CASE(OP_RANGE_INC, B):
+      printf("OP_RANGE_INC\tR%d\n", a);
+      break;
+    CASE(OP_RANGE_EXC, B):
+      printf("OP_RANGE_EXC\tR%d\n", a);
+      break;
+    CASE(OP_DEF, BB):
+      printf("OP_DEF\tR%d\t:%s\n", a, mrb_sym2name(mrb, irep->syms[b]));
+      break;
+    CASE(OP_UNDEF, B):
+      printf("OP_UNDEF\t:%s\n", mrb_sym2name(mrb, irep->syms[a]));
+      break;
+    CASE(OP_ALIAS, BB):
+      printf("OP_ALIAS\t:%s\t%s\n", mrb_sym2name(mrb, irep->syms[a]), mrb_sym2name(mrb, irep->syms[b]));
+      break;
+    CASE(OP_ADD, B):
+      printf("OP_ADD\tR%d\t\n", a);
+      break;
+    CASE(OP_ADDI, BB):
+      printf("OP_ADDI\tR%d\t%d\n", a, b);
+      break;
+    CASE(OP_SUB, B):
+      printf("OP_SUB\tR%d\t\n", a);
+      break;
+    CASE(OP_SUBI, BB):
+      printf("OP_SUBI\tR%d\t%d\n", a, b);
+      break;
+    CASE(OP_MUL, B):
+      printf("OP_MUL\tR%d\t\n", a);
+      break;
+    CASE(OP_DIV, B):
+      printf("OP_DIV\tR%d\t\n", a);
+      break;
+    CASE(OP_LT, B):
+      printf("OP_LT\t\tR%d\t\n", a);
+      break;
+    CASE(OP_LE, B):
+      printf("OP_LE\t\tR%d\t\n", a);
+      break;
+    CASE(OP_GT, B):
+      printf("OP_GT\t\tR%d\t\n", a);
+      break;
+    CASE(OP_GE, B):
+      printf("OP_GE\t\tR%d\t\n", a);
+      break;
+    CASE(OP_EQ, B):
+      printf("OP_EQ\t\tR%d\t\n", a);
+      break;
+    CASE(OP_ARRAY, BB):
+      printf("OP_ARRAY\tR%d\t%d\t", a, b);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_ARRAY2, BBB):
+      printf("OP_ARRAY\tR%d\tR%d\t%d\t", a, b, c);
+      print_lv_ab(mrb, irep, a, b);
       break;
-    case OP_ARYCAT:
-      printf("OP_ARYCAT\tR%d\tR%d\t", GETARG_A(c), GETARG_B(c));
-      print_lv(mrb, irep, c, RAB);
+    CASE(OP_ARYCAT, B):
+      printf("OP_ARYCAT\tR%d\t", a);
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_ARYPUSH:
-      printf("OP_ARYPUSH\tR%d\tR%d\t", GETARG_A(c), GETARG_B(c));
-      print_lv(mrb, irep, c, RAB);
+    CASE(OP_ARYPUSH, B):
+      printf("OP_ARYPUSH\tR%d\t", a);
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_AREF:
-      printf("OP_AREF\tR%d\tR%d\t%d", GETARG_A(c), GETARG_B(c), GETARG_C(c));
-      print_lv(mrb, irep, c, RAB);
+    CASE(OP_ARYDUP, B):
+      printf("OP_ARYDUP\tR%d\t", a);
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_APOST:
-      printf("OP_APOST\tR%d\t%d\t%d", GETARG_A(c), GETARG_B(c), GETARG_C(c));
-      print_lv(mrb, irep, c, RA);
+    CASE(OP_AREF, BBB):
+      printf("OP_AREF\tR%d\tR%d\t%d", a, b, c);
+      print_lv_ab(mrb, irep, a, b);
       break;
-    case OP_STRING:
+    CASE(OP_ASET, BBB):
+      printf("OP_ASET\tR%d\tR%d\t%d", a, b, c);
+      print_lv_ab(mrb, irep, a, b);
+      break;
+    CASE(OP_APOST, BBB):
+      printf("OP_APOST\tR%d\t%d\t%d", a, b, c);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_INTERN, B):
+      printf("OP_INTERN\tR%d", a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_STRING, BB):
       {
-        mrb_value v = irep->pool[GETARG_Bx(c)];
+        mrb_value v = irep->pool[b];
         mrb_value s = mrb_str_dump(mrb, mrb_str_new(mrb, RSTRING_PTR(v), RSTRING_LEN(v)));
-        printf("OP_STRING\tR%d\tL(%d)\t; %s", GETARG_A(c), GETARG_Bx(c), RSTRING_PTR(s));
+        printf("OP_STRING\tR%d\tL(%d)\t; %s", a, b, RSTRING_PTR(s));
       }
-      print_lv(mrb, irep, c, RA);
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_STRCAT:
-      printf("OP_STRCAT\tR%d\tR%d\t", GETARG_A(c), GETARG_B(c));
-      print_lv(mrb, irep, c, RAB);
+    CASE(OP_STRCAT, B):
+      printf("OP_STRCAT\tR%d\t", a);
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_HASH:
-      printf("OP_HASH\tR%d\tR%d\t%d", GETARG_A(c), GETARG_B(c), GETARG_C(c));
-      print_lv(mrb, irep, c, RAB);
+    CASE(OP_HASH, BB):
+      printf("OP_HASH\tR%d\t%d\t", a, b);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_HASHADD, BB):
+      printf("OP_HASHADD\tR%d\t%d\t", a, b);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_HASHCAT, B):
+      printf("OP_HASHCAT\tR%d\t", a);
+      print_lv_a(mrb, irep, a);
       break;
 
-    case OP_OCLASS:
-      printf("OP_OCLASS\tR%d\t\t", GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
+    CASE(OP_OCLASS, B):
+      printf("OP_OCLASS\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_CLASS:
-      printf("OP_CLASS\tR%d\t:%s", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]));
-      print_lv(mrb, irep, c, RA);
+    CASE(OP_CLASS, BB):
+      printf("OP_CLASS\tR%d\t:%s", a, mrb_sym2name(mrb, irep->syms[b]));
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_MODULE:
-      printf("OP_MODULE\tR%d\t:%s", GETARG_A(c),
-             mrb_sym2name(mrb, irep->syms[GETARG_B(c)]));
-      print_lv(mrb, irep, c, RA);
+    CASE(OP_MODULE, BB):
+      printf("OP_MODULE\tR%d\t:%s", a, mrb_sym2name(mrb, irep->syms[b]));
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_EXEC:
-      printf("OP_EXEC\tR%d\tI(%+d)", GETARG_A(c), GETARG_Bx(c)+1);
-      print_lv(mrb, irep, c, RA);
+    CASE(OP_EXEC, BB):
+      printf("OP_EXEC\tR%d\tI(%d:%p)", a, b, irep->reps[b]);
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_SCLASS:
-      printf("OP_SCLASS\tR%d\tR%d\t", GETARG_A(c), GETARG_B(c));
-      print_lv(mrb, irep, c, RAB);
+    CASE(OP_SCLASS, B):
+      printf("OP_SCLASS\tR%d\t", a);
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_TCLASS:
-      printf("OP_TCLASS\tR%d\t\t", GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
+    CASE(OP_TCLASS, B):
+      printf("OP_TCLASS\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
       break;
-    case OP_ERR:
+    CASE(OP_ERR, B):
       {
-        mrb_value v = irep->pool[GETARG_Bx(c)];
+        mrb_value v = irep->pool[a];
         mrb_value s = mrb_str_dump(mrb, mrb_str_new(mrb, RSTRING_PTR(v), RSTRING_LEN(v)));
         printf("OP_ERR\t%s\n", RSTRING_PTR(s));
       }
       break;
-    case OP_EPUSH:
-      printf("OP_EPUSH\t:I(%+d)\n", GETARG_Bx(c)+1);
+    CASE(OP_EPUSH, B):
+      printf("OP_EPUSH\t\t:I(%d:%p)\n", a, irep->reps[a]);
       break;
-    case OP_ONERR:
-      printf("OP_ONERR\t%03d\n", i+GETARG_sBx(c));
+    CASE(OP_ONERR, S):
+      printf("OP_ONERR\t%03d\n", a);
+      break;
+    CASE(OP_EXCEPT, B):
+      printf("OP_EXCEPT\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_RESCUE, BB):
+      printf("OP_RESCUE\tR%d\tR%d", a, b);
+      print_lv_ab(mrb, irep, a, b);
+      break;
+    CASE(OP_RAISE, B):
+      printf("OP_RAISE\tR%d\t\t", a);
+      print_lv_a(mrb, irep, a);
+      break;
+    CASE(OP_POPERR, B):
+      printf("OP_POPERR\t%d\t\t\n", a);
+      break;
+    CASE(OP_EPOP, B):
+      printf("OP_EPOP\t%d\n", a);
       break;
-    case OP_RESCUE:
-      {
-        int a = GETARG_A(c);
-        int b = GETARG_B(c);
-        int cnt = GETARG_C(c);
 
-        if (b == 0) {
-          printf("OP_RESCUE\tR%d\t\t%s", a, cnt ? "cont" : "");
-          print_lv(mrb, irep, c, RA);
-          break;
-        }
-        else {
-          printf("OP_RESCUE\tR%d\tR%d\t%s", a, b, cnt ? "cont" : "");
-          print_lv(mrb, irep, c, RAB);
-          break;
-        }
-      }
+    CASE(OP_DEBUG, BBB):
+      printf("OP_DEBUG\t%d\t%d\t%d\n", a, b, c);
       break;
-    case OP_RAISE:
-      printf("OP_RAISE\tR%d\t\t", GETARG_A(c));
-      print_lv(mrb, irep, c, RA);
+
+    CASE(OP_STOP, Z):
+      printf("OP_STOP\n");
       break;
-    case OP_POPERR:
-      printf("OP_POPERR\t%d\t\t\n", GETARG_A(c));
+
+    CASE(OP_EXT1, Z):
+      ins = READ_B();
+      printf("OP_EXT1\n");
+      print_header(mrb, irep, pc-irep->iseq-2);
+      switch (ins) {
+#define OPCODE(i,x) case OP_ ## i: FETCH_ ## x ## _1 (); goto L_OP_ ## i;
+#include "mruby/ops.h"
+#undef OPCODE
+      }
       break;
-    case OP_EPOP:
-      printf("OP_EPOP\t%d\n", GETARG_A(c));
+    CASE(OP_EXT2, Z):
+      ins = READ_B();
+      printf("OP_EXT2\n");
+      print_header(mrb, irep, pc-irep->iseq-2);
+      switch (ins) {
+#define OPCODE(i,x) case OP_ ## i: FETCH_ ## x ## _2 (); goto L_OP_ ## i;
+#include "mruby/ops.h"
+#undef OPCODE
+      }
+      break;
+    CASE(OP_EXT3, Z):
+      ins = READ_B();
+      printf("OP_EXT3\n");
+      print_header(mrb, irep, pc-irep->iseq-2);
+      switch (ins) {
+#define OPCODE(i,x) case OP_ ## i: FETCH_ ## x ## _3 (); goto L_OP_ ## i;
+#include "mruby/ops.h"
+#undef OPCODE
+      }
       break;
 
     default:
-      printf("OP_unknown %d\t%d\t%d\t%d\n", GET_OPCODE(c),
-             GETARG_A(c), GETARG_B(c), GETARG_C(c));
+      printf("OP_unknown (0x%x)\n", ins);
       break;
     }
     mrb_gc_arena_restore(mrb, ai);
   }
   printf("\n");
-#endif
 }
 
 static void
@@ -469,9 +538,12 @@ codedump_recur(mrb_state *mrb, mrb_irep *irep)
     codedump_recur(mrb, irep->reps[i]);
   }
 }
+#endif
 
 void
 mrb_codedump_all(mrb_state *mrb, struct RProc *proc)
 {
+#ifndef MRB_DISABLE_STDIO
   codedump_recur(mrb, proc->body.irep);
+#endif
 }
diff --git a/src/debug.c b/src/debug.c
index e55f11d4f..0dc02a1e3 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -51,25 +51,25 @@ select_line_type(const uint16_t *lines, size_t lines_len)
 }
 
 MRB_API char const*
-mrb_debug_get_filename(mrb_irep *irep, ptrdiff_t pc)
+mrb_debug_get_filename(mrb_state *mrb, mrb_irep *irep, ptrdiff_t pc)
 {
   if (irep && pc >= 0 && pc < irep->ilen) {
     mrb_irep_debug_info_file* f = NULL;
-    if (!irep->debug_info) { return irep->filename; }
+    if (!irep->debug_info) return NULL;
     else if ((f = get_file(irep->debug_info, (uint32_t)pc))) {
-      return f->filename;
+      return mrb_sym2name_len(mrb, f->filename_sym, NULL);
     }
   }
   return NULL;
 }
 
 MRB_API int32_t
-mrb_debug_get_line(mrb_irep *irep, ptrdiff_t pc)
+mrb_debug_get_line(mrb_state *mrb, mrb_irep *irep, ptrdiff_t pc)
 {
   if (irep && pc >= 0 && pc < irep->ilen) {
     mrb_irep_debug_info_file* f = NULL;
     if (!irep->debug_info) {
-      return irep->lines? irep->lines[pc] : -1;
+      return -1;
     }
     else if ((f = get_file(irep->debug_info, (uint32_t)pc))) {
       switch (f->line_type) {
@@ -122,82 +122,79 @@ mrb_debug_info_alloc(mrb_state *mrb, mrb_irep *irep)
 }
 
 MRB_API mrb_irep_debug_info_file*
-mrb_debug_info_append_file(mrb_state *mrb, mrb_irep *irep,
+mrb_debug_info_append_file(mrb_state *mrb, mrb_irep_debug_info *d,
+                           const char *filename, uint16_t *lines,
                            uint32_t start_pos, uint32_t end_pos)
 {
-  mrb_irep_debug_info *info;
-  mrb_irep_debug_info_file *ret;
+  mrb_irep_debug_info_file *f;
   uint32_t file_pc_count;
   size_t fn_len;
-  mrb_int len;
   uint32_t i;
 
-  if (!irep->debug_info) { return NULL; }
+  if (!d) return NULL;
+  if (start_pos == end_pos) return NULL;
 
-  mrb_assert(irep->filename);
-  mrb_assert(irep->lines);
+  mrb_assert(filename);
+  mrb_assert(lines);
 
-  info = irep->debug_info;
-
-  if (info->flen > 0 && strcmp(irep->filename, info->files[info->flen - 1]->filename) == 0) {
-    return NULL;
+  if (d->flen > 0) {
+    const char *fn = mrb_sym2name_len(mrb, d->files[d->flen - 1]->filename_sym, NULL);
+    if (strcmp(filename, fn) == 0)
+      return NULL;
   }
 
-  ret = (mrb_irep_debug_info_file *)mrb_malloc(mrb, sizeof(*ret));
-  info->files =
-      (mrb_irep_debug_info_file**)(
-          info->files
-          ? mrb_realloc(mrb, info->files, sizeof(mrb_irep_debug_info_file*) * (info->flen + 1))
+  f = (mrb_irep_debug_info_file*)mrb_malloc(mrb, sizeof(*f));
+  d->files = (mrb_irep_debug_info_file**)(
+          d->files
+          ? mrb_realloc(mrb, d->files, sizeof(mrb_irep_debug_info_file*) * (d->flen + 1))
           : mrb_malloc(mrb, sizeof(mrb_irep_debug_info_file*)));
-  info->files[info->flen++] = ret;
+  d->files[d->flen++] = f;
 
   file_pc_count = end_pos - start_pos;
 
-  ret->start_pos = start_pos;
-  info->pc_count = end_pos;
+  f->start_pos = start_pos;
+  d->pc_count = end_pos;
 
-  fn_len = strlen(irep->filename);
-  ret->filename_sym = mrb_intern(mrb, irep->filename, fn_len);
-  len = 0;
-  ret->filename = mrb_sym2name_len(mrb, ret->filename_sym, &len);
+  fn_len = strlen(filename);
+  f->filename_sym = mrb_intern(mrb, filename, fn_len);
 
-  ret->line_type = select_line_type(irep->lines + start_pos, end_pos - start_pos);
-  ret->lines.ptr = NULL;
+  f->line_type = select_line_type(lines + start_pos, end_pos - start_pos);
+  f->lines.ptr = NULL;
 
-  switch (ret->line_type) {
+  switch (f->line_type) {
     case mrb_debug_line_ary:
-      ret->line_entry_count = file_pc_count;
-      ret->lines.ary = (uint16_t*)mrb_malloc(mrb, sizeof(uint16_t) * file_pc_count);
+      f->line_entry_count = file_pc_count;
+      f->lines.ary = (uint16_t*)mrb_malloc(mrb, sizeof(uint16_t) * file_pc_count);
       for (i = 0; i < file_pc_count; ++i) {
-        ret->lines.ary[i] = irep->lines[start_pos + i];
+        f->lines.ary[i] = lines[start_pos + i];
       }
       break;
 
     case mrb_debug_line_flat_map: {
       uint16_t prev_line = 0;
       mrb_irep_debug_info_line m;
-      ret->lines.flat_map = (mrb_irep_debug_info_line*)mrb_malloc(mrb, sizeof(mrb_irep_debug_info_line) * 1);
-      ret->line_entry_count = 0;
+      f->lines.flat_map = (mrb_irep_debug_info_line*)mrb_malloc(mrb, sizeof(mrb_irep_debug_info_line) * 1);
+      f->line_entry_count = 0;
       for (i = 0; i < file_pc_count; ++i) {
-        if (irep->lines[start_pos + i] == prev_line) { continue; }
+        if (lines[start_pos + i] == prev_line) { continue; }
 
-        ret->lines.flat_map = (mrb_irep_debug_info_line*)mrb_realloc(
-            mrb, ret->lines.flat_map,
-            sizeof(mrb_irep_debug_info_line) * (ret->line_entry_count + 1));
+        f->lines.flat_map = (mrb_irep_debug_info_line*)mrb_realloc(
+            mrb, f->lines.flat_map,
+            sizeof(mrb_irep_debug_info_line) * (f->line_entry_count + 1));
         m.start_pos = start_pos + i;
-        m.line = irep->lines[start_pos + i];
-        ret->lines.flat_map[ret->line_entry_count] = m;
+        m.line = lines[start_pos + i];
+        f->lines.flat_map[f->line_entry_count] = m;
 
         /* update */
-        ++ret->line_entry_count;
-        prev_line = irep->lines[start_pos + i];
+        ++f->line_entry_count;
+        prev_line = lines[start_pos + i];
       }
     } break;
 
     default: mrb_assert(0); break;
   }
 
-  return ret;
+  return f;
 }
 
 MRB_API void
diff --git a/src/dump.c b/src/dump.c
index df1e171e4..f1e167e35 100644
--- a/src/dump.c
+++ b/src/dump.c
@@ -6,6 +6,7 @@
 
 #include <string.h>
 #include <limits.h>
+#include <math.h>
 #include <mruby/dump.h>
 #include <mruby/string.h>
 #include <mruby/irep.h>
@@ -17,9 +18,9 @@
 
 #ifndef MRB_WITHOUT_FLOAT
 #ifdef MRB_USE_FLOAT
-#define MRB_FLOAT_FMT "%.8e"
+#define MRB_FLOAT_FMT "%.9g"
 #else
-#define MRB_FLOAT_FMT "%.16e"
+#define MRB_FLOAT_FMT "%.17g"
 #endif
 #endif
 
@@ -81,34 +82,27 @@ static ptrdiff_t
 write_iseq_block(mrb_state *mrb, mrb_irep *irep, uint8_t *buf, uint8_t flags)
 {
   uint8_t *cur = buf;
-  int iseq_no;
 
   cur += uint32_to_bin(irep->ilen, cur); /* number of opcode */
   cur += write_padding(cur);
-  switch (flags & DUMP_ENDIAN_NAT) {
-  case DUMP_ENDIAN_BIG:
-    if (bigendian_p()) goto native;
-    for (iseq_no = 0; iseq_no < irep->ilen; iseq_no++) {
-      cur += uint32_to_bin(irep->iseq[iseq_no], cur); /* opcode */
-    }
-    break;
-  case DUMP_ENDIAN_LIL:
-    if (!bigendian_p()) goto native;
-    for (iseq_no = 0; iseq_no < irep->ilen; iseq_no++) {
-      cur += uint32l_to_bin(irep->iseq[iseq_no], cur); /* opcode */
-    }
-    break;
-
-  native:
-  case DUMP_ENDIAN_NAT:
-    memcpy(cur, irep->iseq, irep->ilen * sizeof(mrb_code));
-    cur += irep->ilen * sizeof(mrb_code);
-    break;
-  }
+  memcpy(cur, irep->iseq, irep->ilen * sizeof(mrb_code));
+  cur += irep->ilen * sizeof(mrb_code);
 
   return cur - buf;
 }
 
+#ifndef MRB_WITHOUT_FLOAT
+static mrb_value
+float_to_str(mrb_state *mrb, mrb_value flt)
+{
+  mrb_float f = mrb_float(flt);
+
+  if (isinf(f)) {
+    return f < 0 ? mrb_str_new_lit(mrb, "I") : mrb_str_new_lit(mrb, "i");
+  }
+  return  mrb_float_to_str(mrb, flt, MRB_FLOAT_FMT);
+}
+#endif
 
 static size_t
 get_pool_block_size(mrb_state *mrb, mrb_irep *irep)
@@ -135,7 +129,7 @@ get_pool_block_size(mrb_state *mrb, mrb_irep *irep)
 
 #ifndef MRB_WITHOUT_FLOAT
     case MRB_TT_FLOAT:
-      str = mrb_float_to_str(mrb, irep->pool[pool_no], MRB_FLOAT_FMT);
+      str = float_to_str(mrb, irep->pool[pool_no]);
       {
         mrb_int len = RSTRING_LEN(str);
         mrb_assert_int_fit(mrb_int, len, size_t, SIZE_MAX);
@@ -184,7 +178,7 @@ write_pool_block(mrb_state *mrb, mrb_irep *irep, uint8_t *buf)
 #ifndef MRB_WITHOUT_FLOAT
     case MRB_TT_FLOAT:
       cur += uint8_to_bin(IREP_TT_FLOAT, cur); /* data type */
-      str = mrb_float_to_str(mrb, irep->pool[pool_no], MRB_FLOAT_FMT);
+      str = float_to_str(mrb, irep->pool[pool_no]);
       break;
 #endif
 
@@ -372,118 +366,6 @@ write_section_irep(mrb_state *mrb, mrb_irep *irep, uint8_t *bin, size_t *len_p,
   return MRB_DUMP_OK;
 }
 
-static int
-write_section_lineno_header(mrb_state *mrb, size_t section_size, uint8_t *bin)
-{
-  struct rite_section_lineno_header *header = (struct rite_section_lineno_header*)bin;
-
-  memcpy(header->section_ident, RITE_SECTION_LINENO_IDENT, sizeof(header->section_ident));
-  uint32_to_bin((uint32_t)section_size, header->section_size);
-
-  return MRB_DUMP_OK;
-}
-
-static size_t
-get_lineno_record_size(mrb_state *mrb, mrb_irep *irep)
-{
-  size_t size = 0;
-
-  size += sizeof(uint32_t); /* record size */
-  size += sizeof(uint16_t); /* filename size */
-  if (irep->filename) {
-    size += strlen(irep->filename); /* filename */
-  }
-  size += sizeof(uint32_t); /* niseq */
-  if (irep->lines) {
-    size += sizeof(uint16_t) * irep->ilen; /* lineno */
-  }
-
-  return size;
-}
-
-static size_t
-write_lineno_record_1(mrb_state *mrb, mrb_irep *irep, uint8_t* bin)
-{
-  uint8_t *cur = bin;
-  int iseq_no;
-  size_t filename_len;
-  ptrdiff_t diff;
-
-  cur += sizeof(uint32_t); /* record size */
-
-  if (irep->filename) {
-    filename_len = strlen(irep->filename);
-  }
-  else {
-    filename_len = 0;
-  }
-  mrb_assert_int_fit(size_t, filename_len, uint16_t, UINT16_MAX);
-  cur += uint16_to_bin((uint16_t)filename_len, cur); /* filename size */
-
-  if (filename_len) {
-    memcpy(cur, irep->filename, filename_len);
-    cur += filename_len; /* filename */
-  }
-
-  if (irep->lines) {
-    mrb_assert_int_fit(size_t, irep->ilen, uint32_t, UINT32_MAX);
-    cur += uint32_to_bin((uint32_t)(irep->ilen), cur); /* niseq */
-    for (iseq_no = 0; iseq_no < irep->ilen; iseq_no++) {
-      cur += uint16_to_bin(irep->lines[iseq_no], cur); /* opcode */
-    }
-  }
-  else {
-    cur += uint32_to_bin(0, cur); /* niseq */
-  }
-
-  diff = cur - bin;
-  mrb_assert_int_fit(ptrdiff_t, diff, uint32_t, UINT32_MAX);
-
-  uint32_to_bin((uint32_t)diff, bin); /* record size */
-
-  mrb_assert_int_fit(ptrdiff_t, diff, size_t, SIZE_MAX);
-  return (size_t)diff;
-}
-
-static size_t
-write_lineno_record(mrb_state *mrb, mrb_irep *irep, uint8_t* bin)
-{
-  size_t rlen, size = 0;
-  int i;
-
-  rlen = write_lineno_record_1(mrb, irep, bin);
-  bin += rlen;
-  size += rlen;
-  for (i=0; i<irep->rlen; i++) {
-    rlen = write_lineno_record(mrb, irep, bin);
-    bin += rlen;
-    size += rlen;
-  }
-  return size;
-}
-
-static int
-write_section_lineno(mrb_state *mrb, mrb_irep *irep, uint8_t *bin)
-{
-  size_t section_size = 0;
-  size_t rlen = 0; /* size of irep record */
-  uint8_t *cur = bin;
-
-  if (mrb == NULL || bin == NULL) {
-    return MRB_DUMP_INVALID_ARGUMENT;
-  }
-
-  cur += sizeof(struct rite_section_lineno_header);
-  section_size += sizeof(struct rite_section_lineno_header);
-
-  rlen = write_lineno_record(mrb, irep, cur);
-  section_size += rlen;
-
-  write_section_lineno_header(mrb, section_size, bin);
-
-  return MRB_DUMP_OK;
-}
-
 static size_t
 get_debug_record_size(mrb_state *mrb, mrb_irep *irep)
 {
@@ -857,26 +739,26 @@ write_rite_binary_header(mrb_state *mrb, size_t binary_size, uint8_t *bin, uint8
 }
 
 static mrb_bool
-is_debug_info_defined(mrb_irep *irep)
+debug_info_defined_p(mrb_irep *irep)
 {
   int i;
 
   if (!irep->debug_info) return FALSE;
   for (i=0; i<irep->rlen; i++) {
-    if (!is_debug_info_defined(irep->reps[i])) return FALSE;
+    if (!debug_info_defined_p(irep->reps[i])) return FALSE;
   }
   return TRUE;
 }
 
 static mrb_bool
-is_lv_defined(mrb_irep *irep)
+lv_defined_p(mrb_irep *irep)
 {
   int i;
 
   if (irep->lv) { return TRUE; }
 
   for (i = 0; i < irep->rlen; ++i) {
-    if (is_lv_defined(irep->reps[i])) { return TRUE; }
+    if (lv_defined_p(irep->reps[i])) { return TRUE; }
   }
 
   return FALSE;
@@ -905,7 +787,7 @@ dump_irep(mrb_state *mrb, mrb_irep *irep, uint8_t flags, uint8_t **bin, size_t *
   size_t section_irep_size;
   size_t section_lineno_size = 0, section_lv_size = 0;
   uint8_t *cur = NULL;
-  mrb_bool const debug_info_defined = is_debug_info_defined(irep), lv_defined = is_lv_defined(irep);
+  mrb_bool const debug_info_defined = debug_info_defined_p(irep), lv_defined = lv_defined_p(irep);
   mrb_sym *lv_syms = NULL; uint32_t lv_syms_len = 0;
   mrb_sym *filenames = NULL; uint16_t filenames_len = 0;
 
@@ -930,10 +812,6 @@ dump_irep(mrb_state *mrb, mrb_irep *irep, uint8_t flags, uint8_t **bin, size_t *
 
       section_lineno_size += get_debug_record_size(mrb, irep);
     }
-    else {
-      section_lineno_size += sizeof(struct rite_section_lineno_header);
-      section_lineno_size += get_lineno_record_size(mrb, irep);
-    }
   }
 
   if (lv_defined) {
@@ -961,12 +839,9 @@ dump_irep(mrb_state *mrb, mrb_irep *irep, uint8_t flags, uint8_t **bin, size_t *
   if (flags & DUMP_DEBUG_INFO) {
     if (debug_info_defined) {
       result = write_section_debug(mrb, irep, cur, filenames, filenames_len);
-    }
-    else {
-      result = write_section_lineno(mrb, irep, cur);
-    }
-    if (result != MRB_DUMP_OK) {
-      goto error_exit;
+      if (result != MRB_DUMP_OK) {
+        goto error_exit;
+      }
     }
     cur += section_lineno_size;
   }
diff --git a/src/enum.c b/src/enum.c
index ea05777b3..1e9445176 100644
--- a/src/enum.c
+++ b/src/enum.c
@@ -14,21 +14,9 @@ enum_update_hash(mrb_state *mrb, mrb_value self)
   mrb_int hash;
   mrb_int index;
   mrb_int hv;
-  mrb_value item_hash;
 
-  mrb_get_args(mrb, "iio", &hash, &index, &item_hash);
-  if (mrb_fixnum_p(item_hash)) {
-    hv = mrb_fixnum(item_hash);
-  }
-#ifndef MRB_WITHOUT_FLOAT
-  else if (mrb_float_p(item_hash)) {
-    hv = (mrb_int)mrb_float(item_hash);
-  }
-#endif
-  else {
-    mrb_raise(mrb, E_TYPE_ERROR, "can't calculate hash");
-  }
-  hash ^= (hv << (index % 16));
+  mrb_get_args(mrb, "iii", &hash, &index, &hv);
+  hash ^= ((uint32_t)hv << (index % 16));
 
   return mrb_fixnum_value(hash);
 }
diff --git a/src/error.c b/src/error.c
index 599612b97..4c1b67c99 100644
--- a/src/error.c
+++ b/src/error.c
@@ -28,7 +28,7 @@ mrb_exc_new(mrb_state *mrb, struct RClass *c, const char *ptr, size_t len)
 MRB_API mrb_value
 mrb_exc_new_str(mrb_state *mrb, struct RClass* c, mrb_value str)
 {
-  str = mrb_str_to_str(mrb, str);
+  mrb_to_str(mrb, str);
   return mrb_obj_new(mrb, c, 1, &str);
 }
 
@@ -208,8 +208,8 @@ exc_debug_info(mrb_state *mrb, struct RObject *exc)
     if (err && ci->proc && !MRB_PROC_CFUNC_P(ci->proc)) {
       mrb_irep *irep = ci->proc->body.irep;
 
-      int32_t const line = mrb_debug_get_line(irep, err - irep->iseq);
-      char const* file = mrb_debug_get_filename(irep, err - irep->iseq);
+      int32_t const line = mrb_debug_get_line(mrb, irep, err - irep->iseq);
+      char const* file = mrb_debug_get_filename(mrb, irep, err - irep->iseq);
       if (line != -1 && file) {
         mrb_obj_iv_set(mrb, exc, mrb_intern_lit(mrb, "file"), mrb_str_new_cstr(mrb, file));
         mrb_obj_iv_set(mrb, exc, mrb_intern_lit(mrb, "line"), mrb_fixnum_value(line));
@@ -376,6 +376,7 @@ mrb_warn(mrb_state *mrb, const char *fmt, ...)
   str = mrb_vformat(mrb, fmt, ap);
   fputs("warning: ", stderr);
   fwrite(RSTRING_PTR(str), RSTRING_LEN(str), 1, stderr);
+  putc('\n', stderr);
   va_end(ap);
 #endif
 }
@@ -483,6 +484,13 @@ mrb_no_method_error(mrb_state *mrb, mrb_sym id, mrb_value args, char const* fmt,
   mrb_exc_raise(mrb, exc);
 }
 
+MRB_API mrb_noreturn void
+mrb_frozen_error(mrb_state *mrb, void *frozen_obj)
+{
+  mrb_raisef(mrb, E_FROZEN_ERROR, "can't modify frozen %S",
+             mrb_obj_value(mrb_class(mrb, mrb_obj_value(frozen_obj))));
+}
+
 void
 mrb_init_exception(mrb_state *mrb)
 {
diff --git a/src/etc.c b/src/etc.c
index 1b8d44a53..18d2839d9 100644
--- a/src/etc.c
+++ b/src/etc.c
@@ -1,5 +1,5 @@
 /*
-** etc.c -
+** etc.c
 **
 ** See Copyright Notice in mruby.h
 */
@@ -8,8 +8,6 @@
 #include <mruby/string.h>
 #include <mruby/data.h>
 #include <mruby/class.h>
-#include <mruby/re.h>
-#include <mruby/irep.h>
 
 MRB_API struct RData*
 mrb_data_object_alloc(mrb_state *mrb, struct RClass *klass, void *ptr, const mrb_data_type *type)
@@ -67,23 +65,10 @@ mrb_data_get_ptr(mrb_state *mrb, mrb_value obj, const mrb_data_type *type)
 MRB_API mrb_sym
 mrb_obj_to_sym(mrb_state *mrb, mrb_value name)
 {
-  mrb_sym id;
-
-  switch (mrb_type(name)) {
-    default:
-      name = mrb_check_string_type(mrb, name);
-      if (mrb_nil_p(name)) {
-        name = mrb_inspect(mrb, name);
-        mrb_raisef(mrb, E_TYPE_ERROR, "%S is not a symbol", name);
-      }
-      /* fall through */
-    case MRB_TT_STRING:
-      name = mrb_str_intern(mrb, name);
-      /* fall through */
-    case MRB_TT_SYMBOL:
-      id = mrb_symbol(name);
-  }
-  return id;
+  if (mrb_symbol_p(name)) return mrb_symbol(name);
+  if (mrb_string_p(name)) return mrb_intern_str(mrb, name);
+  mrb_raisef(mrb, E_TYPE_ERROR, "%S is not a symbol nor a string", mrb_inspect(mrb, name));
+  return 0;  /* not reached */
 }
 
 MRB_API mrb_int
@@ -166,6 +151,7 @@ mrb_word_boxing_float_value(mrb_state *mrb, mrb_float f)
 
   v.value.p = mrb_obj_alloc(mrb, MRB_TT_FLOAT, mrb->float_class);
   v.value.fp->f = f;
+  MRB_SET_FROZEN_FLAG(v.value.bp);
   return v;
 }
 
@@ -176,6 +162,7 @@ mrb_word_boxing_float_pool(mrb_state *mrb, mrb_float f)
   nf->tt = MRB_TT_FLOAT;
   nf->c = mrb->float_class;
   nf->f = f;
+  MRB_SET_FROZEN_FLAG(nf);
   return mrb_obj_value(nf);
 }
 #endif  /* MRB_WITHOUT_FLOAT */
@@ -191,23 +178,6 @@ mrb_word_boxing_cptr_value(mrb_state *mrb, void *p)
 }
 #endif  /* MRB_WORD_BOXING */
 
-MRB_API mrb_bool
-mrb_regexp_p(mrb_state *mrb, mrb_value v)
-{
-  if (mrb->flags & MRB_STATE_NO_REGEXP) {
-    return FALSE;
-  }
-  if ((mrb->flags & MRB_STATE_REGEXP) || mrb_class_defined(mrb, REGEXP_CLASS)) {
-    mrb->flags |= MRB_STATE_REGEXP;
-    return mrb_obj_is_kind_of(mrb, v, mrb_class_get(mrb, REGEXP_CLASS));
-  }
-  else {
-    mrb->flags |= MRB_STATE_REGEXP;
-    mrb->flags |= MRB_STATE_NO_REGEXP;
-  }
-  return FALSE;
-}
-
 #if defined _MSC_VER && _MSC_VER < 1900
 
 #ifndef va_copy
diff --git a/src/ext/.gitkeep b/src/ext/.gitkeep
deleted file mode 100644
index e69de29bb..000000000
--- a/src/ext/.gitkeep
+++ /dev/null
diff --git a/src/fmt_fp.c b/src/fmt_fp.c
index f8a8f7904..1f1af6764 100644
--- a/src/fmt_fp.c
+++ b/src/fmt_fp.c
@@ -1,3 +1,5 @@
+#ifndef MRB_WITHOUT_FLOAT
+#if defined(MRB_DISABLE_STDIO) || defined(_WIN32) || defined(_WIN64)
 /*
 
 Most code in this file originates from musl (src/stdio/vfprintf.c)
@@ -36,7 +38,6 @@ SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #include <mruby.h>
 #include <mruby/string.h>
 
-#ifndef MRB_WITHOUT_FLOAT
 struct fmt_args {
   mrb_state *mrb;
   mrb_value str;
@@ -371,4 +372,17 @@ mrb_float_to_str(mrb_state *mrb, mrb_value flo, const char *fmt)
   }
   return f.str;
 }
+#else   /* MRB_DISABLE_STDIO || _WIN32 || _WIN64 */
+#include <mruby.h>
+#include <stdio.h>
+
+mrb_value
+mrb_float_to_str(mrb_state *mrb, mrb_value flo, const char *fmt)
+{
+  char buf[25];
+
+  snprintf(buf, sizeof(buf), fmt, mrb_float(flo));
+  return mrb_str_new_cstr(mrb, buf);
+}
+#endif  /* MRB_DISABLE_STDIO || _WIN32 || _WIN64 */
 #endif
diff --git a/src/gc.c b/src/gc.c
index 69121d630..b05d929a1 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -10,6 +10,7 @@
 #include <mruby/array.h>
 #include <mruby/class.h>
 #include <mruby/data.h>
+#include <mruby/istruct.h>
 #include <mruby/hash.h>
 #include <mruby/proc.h>
 #include <mruby/range.h>
@@ -109,8 +110,10 @@ typedef struct {
     struct RHash hash;
     struct RRange range;
     struct RData data;
+    struct RIStruct istruct;
     struct RProc proc;
     struct REnv env;
+    struct RFiber fiber;
     struct RException exc;
     struct RBreak brk;
 #ifdef MRB_WORD_BOXING
@@ -274,9 +277,36 @@ mrb_free(mrb_state *mrb, void *p)
   (mrb->allocf)(mrb, p, 0, mrb->allocf_ud);
 }
 
+MRB_API void*
+mrb_alloca(mrb_state *mrb, size_t size)
+{
+  mrb_value str = mrb_str_new(mrb, NULL, size);
+  return RSTRING_PTR(str);
+}
+
+static mrb_bool
+heap_p(mrb_gc *gc, struct RBasic *object)
+{
+  mrb_heap_page* page;
+
+  page = gc->heaps;
+  while (page) {
+    RVALUE *p;
+
+    p = objects(page);
+    if (&p[0].as.basic <= object && object <= &p[MRB_HEAP_PAGE_SIZE].as.basic) {
+      return TRUE;
+    }
+    page = page->next;
+  }
+  return FALSE;
+}
+
 MRB_API mrb_bool
 mrb_object_dead_p(mrb_state *mrb, struct RBasic *object) {
-  return is_dead(&mrb->gc, object);
+  mrb_gc *gc = &mrb->gc;
+  if (!heap_p(gc, object)) return TRUE;
+  return is_dead(gc, object);
 }
 
 static void
@@ -376,7 +406,7 @@ mrb_gc_init(mrb_state *mrb, mrb_gc *gc)
 
 static void obj_free(mrb_state *mrb, struct RBasic *obj, int end);
 
-void
+static void
 free_heap(mrb_state *mrb, mrb_gc *gc)
 {
   mrb_heap_page *page = gc->heaps;
@@ -443,9 +473,12 @@ mrb_gc_protect(mrb_state *mrb, mrb_value obj)
 MRB_API void
 mrb_gc_register(mrb_state *mrb, mrb_value obj)
 {
-  mrb_sym root = mrb_intern_lit(mrb, GC_ROOT_NAME);
-  mrb_value table = mrb_gv_get(mrb, root);
+  mrb_sym root;
+  mrb_value table;
 
+  if (mrb_immediate_p(obj)) return;
+  root = mrb_intern_lit(mrb, GC_ROOT_NAME);
+  table = mrb_gv_get(mrb, root);
   if (mrb_nil_p(table) || mrb_type(table) != MRB_TT_ARRAY) {
     table = mrb_ary_new(mrb);
     mrb_gv_set(mrb, root, table);
@@ -457,11 +490,14 @@ mrb_gc_register(mrb_state *mrb, mrb_value obj)
 MRB_API void
 mrb_gc_unregister(mrb_state *mrb, mrb_value obj)
 {
-  mrb_sym root = mrb_intern_lit(mrb, GC_ROOT_NAME);
-  mrb_value table = mrb_gv_get(mrb, root);
+  mrb_sym root;
+  mrb_value table;
   struct RArray *a;
   mrb_int i;
 
+  if (mrb_immediate_p(obj)) return;
+  root = mrb_intern_lit(mrb, GC_ROOT_NAME);
+  table = mrb_gv_get(mrb, root);
   if (mrb_nil_p(table)) return;
   if (mrb_type(table) != MRB_TT_ARRAY) {
     mrb_gv_set(mrb, root, mrb_nil_value());
@@ -470,7 +506,7 @@ mrb_gc_unregister(mrb_state *mrb, mrb_value obj)
   a = mrb_ary_ptr(table);
   mrb_ary_modify(mrb, a);
   for (i = 0; i < ARY_LEN(a); i++) {
-    if (mrb_obj_eq(mrb, ARY_PTR(a)[i], obj)) {
+    if (mrb_ptr(ARY_PTR(a)[i]) == mrb_ptr(obj)) {
       mrb_int len = ARY_LEN(a)-1;
       mrb_value *ptr = ARY_PTR(a);
 
@@ -548,21 +584,39 @@ add_gray_list(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
   gc->gray_list = obj;
 }
 
+static int
+ci_nregs(mrb_callinfo *ci)
+{
+  struct RProc *p = ci->proc;
+  int n = 0;
+
+  if (!p) {
+    if (ci->argc < 0) return 3;
+    return ci->argc+2;
+  }
+  if (!MRB_PROC_CFUNC_P(p) && p->body.irep) {
+    n = p->body.irep->nregs;
+  }
+  if (ci->argc < 0) {
+    if (n < 3) n = 3; /* self + args + blk */
+  }
+  if (ci->argc > n) {
+    n = ci->argc + 2; /* self + blk */
+  }
+  return n;
+}
+
 static void
 mark_context_stack(mrb_state *mrb, struct mrb_context *c)
 {
   size_t i;
   size_t e;
   mrb_value nil;
-  mrb_int nregs;
 
   if (c->stack == NULL) return;
   e = c->stack - c->stbase;
   if (c->ci) {
-    nregs = c->ci->argc + 2;
-    if (c->ci->nregs > nregs)
-      nregs = c->ci->nregs;
-    e += nregs;
+    e += ci_nregs(c->ci);
   }
   if (c->stbase + e > c->stend) e = c->stend - c->stbase;
   for (i=0; i<e; i++) {
@@ -622,7 +676,7 @@ gc_mark_children(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
   case MRB_TT_ICLASS:
     {
       struct RClass *c = (struct RClass*)obj;
-      if (MRB_FLAG_TEST(c, MRB_FLAG_IS_ORIGIN))
+      if (MRB_FLAG_TEST(c, MRB_FL_CLASS_IS_ORIGIN))
         mrb_gc_mark_mt(mrb, c);
       mrb_gc_mark(mrb, (struct RBasic*)((struct RClass*)obj)->super);
     }
@@ -701,14 +755,7 @@ gc_mark_children(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
     break;
 
   case MRB_TT_RANGE:
-    {
-      struct RRange *r = (struct RRange*)obj;
-
-      if (r->edges) {
-        mrb_gc_mark_value(mrb, r->edges->beg);
-        mrb_gc_mark_value(mrb, r->edges->end);
-      }
-    }
+    mrb_gc_mark_range(mrb, (struct RRange*)obj);
     break;
 
   default:
@@ -761,7 +808,7 @@ obj_free(mrb_state *mrb, struct RBasic *obj, int end)
     mrb_gc_free_iv(mrb, (struct RObject*)obj);
     break;
   case MRB_TT_ICLASS:
-    if (MRB_FLAG_TEST(obj, MRB_FLAG_IS_ORIGIN))
+    if (MRB_FLAG_TEST(obj, MRB_FL_CLASS_IS_ORIGIN))
       mrb_gc_free_mt(mrb, (struct RClass*)obj);
     break;
   case MRB_TT_ENV:
@@ -770,7 +817,8 @@ obj_free(mrb_state *mrb, struct RBasic *obj, int end)
 
       if (MRB_ENV_STACK_SHARED_P(e)) {
         /* cannot be freed */
-        return;
+        e->stack = NULL;
+        break;
       }
       mrb_free(mrb, e->stack);
       e->stack = NULL;
@@ -782,13 +830,13 @@ obj_free(mrb_state *mrb, struct RBasic *obj, int end)
       struct mrb_context *c = ((struct RFiber*)obj)->cxt;
 
       if (c && c != mrb->root_c) {
-        mrb_callinfo *ci = c->ci;
-        mrb_callinfo *ce = c->cibase;
+        if (!end && c->status != MRB_FIBER_TERMINATED) {
+          mrb_callinfo *ci = c->ci;
+          mrb_callinfo *ce = c->cibase;
 
-        if (!end) {
           while (ce <= ci) {
             struct REnv *e = ci->env;
-            if (e && !is_dead(&mrb->gc, e) &&
+            if (e && !mrb_object_dead_p(mrb, (struct RBasic*)e) &&
                 e->tt == MRB_TT_ENV && MRB_ENV_STACK_SHARED_P(e)) {
               mrb_env_unshare(mrb, e);
             }
@@ -831,7 +879,7 @@ obj_free(mrb_state *mrb, struct RBasic *obj, int end)
     break;
 
   case MRB_TT_RANGE:
-    mrb_free(mrb, ((struct RRange*)obj)->edges);
+    mrb_gc_free_range(mrb, ((struct RRange*)obj));
     break;
 
   case MRB_TT_DATA:
@@ -947,10 +995,14 @@ gc_gray_mark(mrb_state *mrb, mrb_gc *gc, struct RBasic *obj)
       size_t i;
       mrb_callinfo *ci;
 
-      if (!c) break;
+      if (!c || c->status == MRB_FIBER_TERMINATED) break;
+
       /* mark stack */
       i = c->stack - c->stbase;
-      if (c->ci) i += c->ci->nregs;
+
+      if (c->ci) {
+        i += ci_nregs(c->ci);
+      }
       if (c->stbase + i > c->stend) i = c->stend - c->stbase;
       children += i;
 
@@ -1537,7 +1589,7 @@ mrb_objspace_each_objects(mrb_state *mrb, mrb_each_object_callback *callback, vo
       mrb->jmp = &c_jmp;
       gc_each_objects(mrb, &mrb->gc, callback, data);
       mrb->jmp = prev_jmp;
-      mrb->gc.iterating = iterating; 
+      mrb->gc.iterating = iterating;
    } MRB_CATCH(&c_jmp) {
       mrb->gc.iterating = iterating;
       mrb->jmp = prev_jmp;
diff --git a/src/hash.c b/src/hash.c
index db9d1d9c8..2a0a19363 100644
--- a/src/hash.c
+++ b/src/hash.c
@@ -8,7 +8,6 @@
 #include <mruby/array.h>
 #include <mruby/class.h>
 #include <mruby/hash.h>
-#include <mruby/khash.h>
 #include <mruby/string.h>
 #include <mruby/variable.h>
 
@@ -17,14 +16,47 @@
 mrb_int mrb_float_id(mrb_float f);
 #endif
 
-static inline khint_t
-mrb_hash_ht_hash_func(mrb_state *mrb, mrb_value key)
+#ifndef MRB_HT_INIT_SIZE
+#define MRB_HT_INIT_SIZE 4
+#endif
+#define HT_SEG_INCREASE_RATIO 6 / 5
+
+struct segkv {
+  mrb_value key;
+  mrb_value val;
+};
+
+typedef struct segment {
+  uint16_t size;
+  struct segment *next;
+  struct segkv e[];
+} segment;
+
+typedef struct segindex {
+  size_t size;
+  size_t capa;
+  struct segkv *table[];
+} segindex;
+
+/* hash table structure */
+typedef struct htable {
+  segment *rootseg;
+  segment *lastseg;
+  mrb_int size;
+  uint16_t last_len;
+  segindex *index;
+} htable;
+
+static /* inline */ size_t
+ht_hash_func(mrb_state *mrb, htable *t, mrb_value key)
 {
-  enum mrb_vtype t = mrb_type(key);
+  enum mrb_vtype tt = mrb_type(key);
   mrb_value hv;
-  khint_t h;
+  size_t h;
+  segindex *index = t->index;
+  size_t capa = index ? index->capa : 0;
 
-  switch (t) {
+  switch (tt) {
   case MRB_TT_STRING:
     h = mrb_str_hash(mrb, key);
     break;
@@ -36,23 +68,26 @@ mrb_hash_ht_hash_func(mrb_state *mrb, mrb_value key)
 #ifndef MRB_WITHOUT_FLOAT
   case MRB_TT_FLOAT:
 #endif
-    h = (khint_t)mrb_obj_id(key);
+    h = (size_t)mrb_obj_id(key);
     break;
 
   default:
     hv = mrb_funcall(mrb, key, "hash", 0);
-    h = (khint_t)t ^ (khint_t)mrb_fixnum(hv);
+    h = (size_t)t ^ (size_t)mrb_fixnum(hv);
     break;
   }
-  return kh_int_hash_func(mrb, h);
+  if (index && (index != t->index || capa != index->capa)) {
+    mrb_raise(mrb, E_RUNTIME_ERROR, "hash modified");
+  }
+  return ((h)^((h)<<2)^((h)>>2));
 }
 
-static inline khint_t
-mrb_hash_ht_hash_equal(mrb_state *mrb, mrb_value a, mrb_value b)
+static inline mrb_bool
+ht_hash_equal(mrb_state *mrb, htable *t, mrb_value a, mrb_value b)
 {
-  enum mrb_vtype t = mrb_type(a);
+  enum mrb_vtype tt = mrb_type(a);
 
-  switch (t) {
+  switch (tt) {
   case MRB_TT_STRING:
     return mrb_str_equal(mrb, a, b);
 
@@ -85,16 +120,461 @@ mrb_hash_ht_hash_equal(mrb_state *mrb, mrb_value a, mrb_value b)
 #endif
 
   default:
-    return mrb_eql(mrb, a, b);
+    {
+      segindex *index = t->index;
+      size_t capa = index ? index->capa : 0;
+      mrb_bool eql = mrb_eql(mrb, a, b);
+      if (index && (index != t->index || capa != index->capa)) {
+        mrb_raise(mrb, E_RUNTIME_ERROR, "hash modified");
+      }
+      return eql;
+    }
+  } 
+}
+
+/* Creates the hash table. */
+static htable*
+ht_new(mrb_state *mrb)
+{
+  htable *t;
+
+  t = (htable*)mrb_malloc(mrb, sizeof(htable));
+  t->size = 0;
+  t->rootseg =  NULL;
+  t->lastseg =  NULL;
+  t->last_len = 0;
+  t->index = NULL;
+
+  return t;
+}
+
+#define power2(v) do { \
+  v--;\
+  v |= v >> 1;\
+  v |= v >> 2;\
+  v |= v >> 4;\
+  v |= v >> 8;\
+  v |= v >> 16;\
+  v++;\
+} while (0)
+
+#ifndef UPPER_BOUND
+#define UPPER_BOUND(x) ((x)>>2|(x)>>1)
+#endif
+
+#define HT_MASK(index) ((index->capa)-1)
+
+/* Build index for the hash table */
+static void
+ht_index(mrb_state *mrb, htable *t)
+{
+  size_t size = (size_t)t->size;
+  size_t mask;
+  segindex *index = t->index;
+  segment *seg;
+  size_t i;
+
+  /* allocate index table */
+  if (index && index->size >= UPPER_BOUND(index->capa)) {
+    size = index->capa+1;
+  }
+  power2(size);
+  if (!index || index->capa < size) {
+    index = (segindex*)mrb_realloc_simple(mrb, index, sizeof(segindex)+sizeof(struct segkv*)*size);
+    if (index == NULL) {
+      mrb_free(mrb, t->index);
+      t->index = NULL;
+      return;
+    }
+    t->index = index;
+  }
+  index->size = t->size;
+  index->capa = size;
+  for (i=0; i<size; i++) {
+    index->table[i] = NULL;
+  }
+
+  /* rebuld index */
+  mask = HT_MASK(index);
+  seg = t->rootseg;
+  while (seg) {
+    for (i=0; i<seg->size; i++) {
+      mrb_value key;
+      size_t k, step = 0;
+
+      if (!seg->next && i >= (size_t)t->last_len) {
+        return;
+      }
+      key = seg->e[i].key;
+      if (mrb_undef_p(key)) continue;
+      k = ht_hash_func(mrb, t, key) & mask;
+      while (index->table[k]) {
+        k = (k+(++step)) & mask;
+      }
+      index->table[k] = &seg->e[i];
+    }
+    seg = seg->next;
+  }
+}
+
+/* Compacts the hash table removing deleted entries. */
+static void
+ht_compact(mrb_state *mrb, htable *t)
+{
+  segment *seg;
+  mrb_int i;
+  segment *seg2 = NULL;
+  mrb_int i2;
+  mrb_int size = 0;
+
+  if (t == NULL) return;
+  seg = t->rootseg;
+  if (t->index && (size_t)t->size == t->index->size) {
+    ht_index(mrb, t);
+    return;
+  }
+  while (seg) {
+    for (i=0; i<seg->size; i++) {
+      mrb_value k = seg->e[i].key;
+
+      if (!seg->next && i >= t->last_len) {
+        goto exit;
+      }
+      if (mrb_undef_p(k)) {     /* found deleted key */
+        if (seg2 == NULL) {
+          seg2 = seg;
+          i2 = i;
+        }
+      }
+      else {
+        size++;
+        if (seg2 != NULL) {
+          seg2->e[i2++] = seg->e[i];
+          if (i2 >= seg2->size) {
+            seg2 = seg2->next;
+            i2 = 0;
+          }
+        }
+      }
+    }
+    seg = seg->next;
+  }
+ exit:
+  /* reached at end */
+  t->size = size;
+  if (seg2) {
+    seg = seg2->next;
+    seg2->next = NULL;
+    t->last_len = i2;
+    t->lastseg = seg2;
+    while (seg) {
+      seg2 = seg->next;
+      mrb_free(mrb, seg);
+      seg = seg2;
+    }
+  }
+  if (t->index) {
+    ht_index(mrb, t);
+  }
+}
+
+static segment*
+segment_alloc(mrb_state *mrb, segment *seg)
+{
+  uint32_t size;
+
+  if (!seg) size = MRB_HT_INIT_SIZE;
+  else {
+    size = seg->size*HT_SEG_INCREASE_RATIO + 1;
+    if (size > UINT16_MAX) size = UINT16_MAX;
+  }
+
+  seg = (segment*)mrb_malloc(mrb, sizeof(segment)+sizeof(struct segkv)*size);
+  seg->size = size;
+  seg->next = NULL;
+
+  return seg;
+}
+
+/* Set the value for the key in the indexed table. */
+static void
+ht_index_put(mrb_state *mrb, htable *t, mrb_value key, mrb_value val)
+{
+  segindex *index = t->index;
+  size_t k, sp, step = 0, mask;
+  segment *seg;
+
+  if (index->size >= UPPER_BOUND(index->capa)) {
+    /* need to expand table */
+    ht_compact(mrb, t);
+    index = t->index;
+  }
+  mask = HT_MASK(index);
+  sp = index->capa;
+  k = ht_hash_func(mrb, t, key) & mask;
+  while (index->table[k]) {
+    mrb_value key2 = index->table[k]->key;
+    if (mrb_undef_p(key2)) {
+      if (sp == index->capa) sp = k;
+    }
+    else if (ht_hash_equal(mrb, t, key, key2)) {
+      index->table[k]->val = val;
+      return;
+    }
+    k = (k+(++step)) & mask;
+  }
+  if (sp < index->capa) {
+    k = sp;
+  }
+
+  /* put the value at the last */
+  seg = t->lastseg;
+  if (t->last_len < seg->size) {
+    index->table[k] = &seg->e[t->last_len++];
+  }
+  else {                        /* append a new segment */
+    seg->next = segment_alloc(mrb, seg);
+    seg = seg->next;
+    seg->next = NULL;
+    t->lastseg = seg;
+    t->last_len = 1;
+    index->table[k] = &seg->e[0];
+  }
+  index->table[k]->key = key;
+  index->table[k]->val = val;
+  index->size++;
+  t->size++;
+}
+
+/* Set the value for the key in the hash table. */
+static void
+ht_put(mrb_state *mrb, htable *t, mrb_value key, mrb_value val)
+{
+  segment *seg;
+  mrb_int i, deleted = 0;
+
+  if (t == NULL) return;
+  if (t->index) {
+    ht_index_put(mrb, t, key, val);
+    return;
+  }
+  seg = t->rootseg;
+  while (seg) {
+    for (i=0; i<seg->size; i++) {
+      mrb_value k = seg->e[i].key;
+      /* Found room in last segment after last_len */
+      if (!seg->next && i >= t->last_len) {
+        seg->e[i].key = key;
+        seg->e[i].val = val;
+        t->last_len = i+1;
+        t->size++;
+        return;
+      }
+      if (mrb_undef_p(k)) {
+        deleted++;
+        continue;
+      }
+      if (ht_hash_equal(mrb, t, k, key)) {
+        seg->e[i].val = val;
+        return;
+      }
+    }
+    seg = seg->next;
+  }
+  /* Not found */
+
+  /* Compact if last segment has room */
+  if (deleted > 0 && deleted > MRB_HT_INIT_SIZE) {
+    ht_compact(mrb, t);
+  }
+  t->size++;
+
+  /* check if thre's room after compaction */
+  if (t->lastseg && t->last_len < t->lastseg->size) {
+    seg = t->lastseg;
+    i = t->last_len;
+  }
+  else {
+    /* append new segment */
+    seg = segment_alloc(mrb, t->lastseg);
+    i = 0;
+    if (t->rootseg == NULL) {
+      t->rootseg = seg;
+    }
+    else {
+      t->lastseg->next = seg;
+    }
+    t->lastseg = seg;
+  }
+  seg->e[i].key = key;
+  seg->e[i].val = val;
+  t->last_len = i+1;
+  if (t->index == NULL && t->size > MRB_HT_INIT_SIZE*4) {
+    ht_index(mrb, t);
   }
 }
 
-KHASH_DEFINE (ht, mrb_value, mrb_hash_value, TRUE, mrb_hash_ht_hash_func, mrb_hash_ht_hash_equal)
+/* Get a value for a key from the indexed table. */
+static mrb_bool
+ht_index_get(mrb_state *mrb, htable *t, mrb_value key, mrb_value *vp)
+{
+  segindex *index = t->index;
+  size_t mask = HT_MASK(index);
+  size_t k = ht_hash_func(mrb, t, key) & mask;
+  size_t step = 0;
+
+  while (index->table[k]) {
+    mrb_value key2 = index->table[k]->key;
+    if (!mrb_undef_p(key2) && ht_hash_equal(mrb, t, key, key2)) {
+      if (vp) *vp = index->table[k]->val;
+      return TRUE;
+    }
+    k = (k+(++step)) & mask;
+  }
+  return FALSE;
+}
+
+/* Get a value for a key from the hash table. */
+static mrb_bool
+ht_get(mrb_state *mrb, htable *t, mrb_value key, mrb_value *vp)
+{
+  segment *seg;
+  mrb_int i;
+
+  if (t == NULL) return FALSE;
+  if (t->index) {
+    return ht_index_get(mrb, t, key, vp);
+  }
+
+  seg = t->rootseg;
+  while (seg) {
+    for (i=0; i<seg->size; i++) {
+      mrb_value k = seg->e[i].key;
+
+      if (!seg->next && i >= t->last_len) {
+        return FALSE;
+      }
+      if (mrb_undef_p(k)) continue;
+      if (ht_hash_equal(mrb, t, k, key)) {
+        if (vp) *vp = seg->e[i].val;
+        return TRUE;
+      }
+    }
+    seg = seg->next;
+  }
+  return FALSE;
+}
+
+/* Deletes the value for the symbol from the hash table. */
+/* Deletion is done by overwriting keys by `undef`. */
+static mrb_bool
+ht_del(mrb_state *mrb, htable *t, mrb_value key, mrb_value *vp)
+{
+  segment *seg;
+  mrb_int i;
+
+  if (t == NULL) return FALSE;
+  seg = t->rootseg;
+  while (seg) {
+    for (i=0; i<seg->size; i++) {
+      mrb_value key2;
+
+      if (!seg->next && i >= t->last_len) {
+        /* not found */
+        return FALSE;
+      }
+      key2 = seg->e[i].key;
+      if (!mrb_undef_p(key2) && ht_hash_equal(mrb, t, key, key2)) {
+        if (vp) *vp = seg->e[i].val;
+        seg->e[i].key = mrb_undef_value();
+        t->size--;
+        return TRUE;
+      }
+    }
+    seg = seg->next;
+  }
+  return FALSE;
+}
+
+/* Iterates over the hash table. */
+static void
+ht_foreach(mrb_state *mrb, htable *t, mrb_hash_foreach_func *func, void *p)
+{
+  segment *seg;
+  mrb_int i;
+
+  if (t == NULL) return;
+  seg = t->rootseg;
+  while (seg) {
+    for (i=0; i<seg->size; i++) {
+      /* no value in last segment after last_len */
+      if (!seg->next && i >= t->last_len) {
+        return;
+      }
+      if (mrb_undef_p(seg->e[i].key)) continue;
+      if ((*func)(mrb, seg->e[i].key, seg->e[i].val, p) != 0)
+        return;
+    }
+    seg = seg->next;
+  }
+}
+
+/* Iterates over the hash table. */
+MRB_API void
+mrb_hash_foreach(mrb_state *mrb, struct RHash *hash, mrb_hash_foreach_func *func, void *p)
+{
+  ht_foreach(mrb, hash->ht, func, p);
+}
+
+/* Copy the hash table. */
+static htable*
+ht_copy(mrb_state *mrb, htable *t)
+{
+  segment *seg;
+  htable *t2;
+  mrb_int i;
+
+  seg = t->rootseg;
+  t2 = ht_new(mrb);
+  if (t->size == 0) return t2;
+
+  while (seg) {
+    for (i=0; i<seg->size; i++) {
+      mrb_value key = seg->e[i].key;
+      mrb_value val = seg->e[i].val;
+
+      if ((seg->next == NULL) && (i >= t->last_len)) {
+        return t2;
+      }
+      if (mrb_undef_p(key)) continue; /* skip deleted key */
+      ht_put(mrb, t2, key, val);
+    }
+    seg = seg->next;
+  }
+  return t2;
+}
+
+/* Free memory of the hash table. */
+static void
+ht_free(mrb_state *mrb, htable *t)
+{
+  segment *seg;
+
+  if (!t) return;
+  seg = t->rootseg;
+  while (seg) {
+    segment *p = seg;
+    seg = seg->next;
+    mrb_free(mrb, p);
+  }
+  if (t->index) mrb_free(mrb, t->index);
+  mrb_free(mrb, t);
+}
 
 static void mrb_hash_modify(mrb_state *mrb, mrb_value hash);
 
 static inline mrb_value
-mrb_hash_ht_key(mrb_state *mrb, mrb_value key)
+ht_key(mrb_state *mrb, mrb_value key)
 {
   if (mrb_string_p(key) && !MRB_FROZEN_P(mrb_str_ptr(key))) {
     key = mrb_str_dup(mrb, key);
@@ -103,59 +583,57 @@ mrb_hash_ht_key(mrb_state *mrb, mrb_value key)
   return key;
 }
 
-#define KEY(key) mrb_hash_ht_key(mrb, key)
+#define KEY(key) ht_key(mrb, key)
+
+static int
+hash_mark_i(mrb_state *mrb, mrb_value key, mrb_value val, void *p)
+{
+  mrb_gc_mark_value(mrb, key);
+  mrb_gc_mark_value(mrb, val);
+  return 0;
+}
 
 void
 mrb_gc_mark_hash(mrb_state *mrb, struct RHash *hash)
 {
-  khiter_t k;
-  khash_t(ht) *h = hash->ht;
-
-  if (!h) return;
-  for (k = kh_begin(h); k != kh_end(h); k++) {
-    if (kh_exist(h, k)) {
-      mrb_value key = kh_key(h, k);
-      mrb_value val = kh_value(h, k).v;
-
-      mrb_gc_mark_value(mrb, key);
-      mrb_gc_mark_value(mrb, val);
-    }
-  }
+  ht_foreach(mrb, hash->ht, hash_mark_i, NULL);
 }
 
 size_t
 mrb_gc_mark_hash_size(mrb_state *mrb, struct RHash *hash)
 {
   if (!hash->ht) return 0;
-  return kh_size(hash->ht)*2;
+  return hash->ht->size*2;
 }
 
 void
 mrb_gc_free_hash(mrb_state *mrb, struct RHash *hash)
 {
-  if (hash->ht) kh_destroy(ht, mrb, hash->ht);
+  ht_free(mrb, hash->ht);
 }
 
-
 MRB_API mrb_value
-mrb_hash_new_capa(mrb_state *mrb, mrb_int capa)
+mrb_hash_new(mrb_state *mrb)
 {
   struct RHash *h;
 
   h = (struct RHash*)mrb_obj_alloc(mrb, MRB_TT_HASH, mrb->hash_class);
-  /* khash needs 1/4 empty space so it is not resized immediately */
-  if (capa == 0)
-    h->ht = 0;
-  else
-    h->ht = kh_init_size(ht, mrb, (khint_t)(capa*4/3));
+  h->ht = 0;
   h->iv = 0;
   return mrb_obj_value(h);
 }
 
 MRB_API mrb_value
-mrb_hash_new(mrb_state *mrb)
+mrb_hash_new_capa(mrb_state *mrb, mrb_int capa)
 {
-  return mrb_hash_new_capa(mrb, 0);
+  struct RHash *h;
+
+  h = (struct RHash*)mrb_obj_alloc(mrb, MRB_TT_HASH, mrb->hash_class);
+  /* preallocate hash table */
+  h->ht = ht_new(mrb);
+  /* capacity ignored */
+  h->iv = 0;
+  return mrb_obj_value(h);
 }
 
 static mrb_value mrb_hash_default(mrb_state *mrb, mrb_value hash);
@@ -166,7 +644,7 @@ mrb_hash_init_copy(mrb_state *mrb, mrb_value self)
 {
   mrb_value orig;
   struct RHash* copy;
-  khash_t(ht) *orig_h;
+  htable *orig_h;
   mrb_value ifnone, vret;
 
   mrb_get_args(mrb, "o", &orig);
@@ -177,22 +655,7 @@ mrb_hash_init_copy(mrb_state *mrb, mrb_value self)
 
   orig_h = RHASH_TBL(self);
   copy = (struct RHash*)mrb_obj_alloc(mrb, MRB_TT_HASH, mrb->hash_class);
-  copy->ht = kh_init(ht, mrb);
-
-  if (orig_h && kh_size(orig_h) > 0) {
-    khash_t(ht) *copy_h = copy->ht;
-    khiter_t k, copy_k;
-
-    for (k = kh_begin(orig_h); k != kh_end(orig_h); k++) {
-      if (kh_exist(orig_h, k)) {
-        int ai = mrb_gc_arena_save(mrb);
-        copy_k = kh_put(ht, mrb, copy_h, KEY(kh_key(orig_h, k)));
-        mrb_gc_arena_restore(mrb, ai);
-        kh_val(copy_h, copy_k).v = kh_val(orig_h, k).v;
-        kh_val(copy_h, copy_k).n = kh_size(copy_h)-1;
-      }
-    }
-  }
+  copy->ht = ht_copy(mrb, orig_h);
 
   if (MRB_RHASH_DEFAULT_P(self)) {
     copy->flags |= MRB_HASH_DEFAULT;
@@ -208,17 +671,45 @@ mrb_hash_init_copy(mrb_state *mrb, mrb_value self)
   return vret;
 }
 
+static int
+check_kdict_i(mrb_state *mrb, mrb_value key, mrb_value val, void *data)
+{
+  if (!mrb_symbol_p(key)) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "keyword argument hash with non symbol keys");
+  }
+  return 0;
+}
+
+void
+mrb_hash_check_kdict(mrb_state *mrb, mrb_value self)
+{
+  htable *t;
+
+  t = RHASH_TBL(self);
+  if (!t || t->size == 0) return;
+  ht_foreach(mrb, t, check_kdict_i, NULL);
+}
+
+MRB_API mrb_value
+mrb_hash_dup(mrb_state *mrb, mrb_value self)
+{
+  struct RHash* copy;
+  htable *orig_h;
+
+  orig_h = RHASH_TBL(self);
+  copy = (struct RHash*)mrb_obj_alloc(mrb, MRB_TT_HASH, mrb->hash_class);
+  copy->ht = orig_h ? ht_copy(mrb, orig_h) : NULL;
+  return mrb_obj_value(copy);
+}
+
 MRB_API mrb_value
 mrb_hash_get(mrb_state *mrb, mrb_value hash, mrb_value key)
 {
-  khash_t(ht) *h = RHASH_TBL(hash);
-  khiter_t k;
+  mrb_value val;
   mrb_sym mid;
 
-  if (h) {
-    k = kh_get(ht, mrb, h, key);
-    if (k != kh_end(h))
-      return kh_value(h, k).v;
+  if (ht_get(mrb, RHASH_TBL(hash), key, &val)) {
+    return val;
   }
 
   mid = mrb_intern_lit(mrb, "default");
@@ -232,15 +723,11 @@ mrb_hash_get(mrb_state *mrb, mrb_value hash, mrb_value key)
 MRB_API mrb_value
 mrb_hash_fetch(mrb_state *mrb, mrb_value hash, mrb_value key, mrb_value def)
 {
-  khash_t(ht) *h = RHASH_TBL(hash);
-  khiter_t k;
+  mrb_value val;
 
-  if (h) {
-    k = kh_get(ht, mrb, h, key);
-    if (k != kh_end(h))
-      return kh_value(h, k).v;
+  if (ht_get(mrb, RHASH_TBL(hash), key, &val)) {
+    return val;
   }
-
   /* not found */
   return def;
 }
@@ -248,54 +735,22 @@ mrb_hash_fetch(mrb_state *mrb, mrb_value hash, mrb_value key, mrb_value def)
 MRB_API void
 mrb_hash_set(mrb_state *mrb, mrb_value hash, mrb_value key, mrb_value val)
 {
-  khash_t(ht) *h;
-  khiter_t k;
-  int r;
-
   mrb_hash_modify(mrb, hash);
-  h = RHASH_TBL(hash);
-
-  if (!h) h = RHASH_TBL(hash) = kh_init(ht, mrb);
-  k = kh_put2(ht, mrb, h, key, &r);
-  kh_value(h, k).v = val;
-
-  if (r != 0) {
-    /* expand */
-    int ai = mrb_gc_arena_save(mrb);
-    key = kh_key(h, k) = KEY(key);
-    mrb_gc_arena_restore(mrb, ai);
-    kh_value(h, k).n = kh_size(h)-1;
-  }
 
+  key = KEY(key);
+  ht_put(mrb, RHASH_TBL(hash), key, val);
   mrb_field_write_barrier_value(mrb, (struct RBasic*)RHASH(hash), key);
   mrb_field_write_barrier_value(mrb, (struct RBasic*)RHASH(hash), val);
   return;
 }
 
-MRB_API mrb_value
-mrb_check_hash_type(mrb_state *mrb, mrb_value hash)
-{
-  return mrb_check_convert_type(mrb, hash, MRB_TT_HASH, "Hash", "to_hash");
-}
-
-MRB_API khash_t(ht)*
-mrb_hash_tbl(mrb_state *mrb, mrb_value hash)
-{
-  khash_t(ht) *h = RHASH_TBL(hash);
-
-  if (!h) {
-    return RHASH_TBL(hash) = kh_init(ht, mrb);
-  }
-  return h;
-}
-
 static void
 mrb_hash_modify(mrb_state *mrb, mrb_value hash)
 {
-  if (MRB_FROZEN_P(mrb_hash_ptr(hash))) {
-    mrb_raise(mrb, E_FROZEN_ERROR, "can't modify frozen hash");
+  mrb_check_frozen(mrb, mrb_hash_ptr(hash));
+  if (!RHASH_TBL(hash)) {
+    RHASH_TBL(hash) = ht_new(mrb);
   }
-  mrb_hash_tbl(mrb, hash);
 }
 
 /* 15.2.13.4.16 */
@@ -535,47 +990,17 @@ mrb_hash_set_default_proc(mrb_state *mrb, mrb_value hash)
 MRB_API mrb_value
 mrb_hash_delete_key(mrb_state *mrb, mrb_value hash, mrb_value key)
 {
-  khash_t(ht) *h = RHASH_TBL(hash);
-  khiter_t k;
-  mrb_value delVal;
-  mrb_int n;
-
-  if (h) {
-    k = kh_get(ht, mrb, h, key);
-    if (k != kh_end(h)) {
-      delVal = kh_value(h, k).v;
-      n = kh_value(h, k).n;
-      kh_del(ht, mrb, h, k);
-      for (k = kh_begin(h); k != kh_end(h); k++) {
-        if (!kh_exist(h, k)) continue;
-        if (kh_value(h, k).n > n) kh_value(h, k).n--;
-      }
-      return delVal;
-    }
+  htable *t = RHASH_TBL(hash);
+  mrb_value del_val;
+
+  if (ht_del(mrb, t, key, &del_val)) {
+    return del_val;
   }
 
   /* not found */
   return mrb_nil_value();
 }
 
-/* 15.2.13.4.8  */
-/*
- *  call-seq:
- *     hsh.delete(key)                   -> value
- *     hsh.delete(key) {| key | block }  -> value
- *
- *  Deletes and returns a key-value pair from <i>hsh</i> whose key is
- *  equal to <i>key</i>. If the key is not found, returns the
- *  <em>default value</em>. If the optional code block is given and the
- *  key is not found, pass in the key and return the result of
- *  <i>block</i>.
- *
- *      h = { "a" => 100, "b" => 200 }
- *      h.delete("a")                              #=> 100
- *      h.delete("z")                              #=> nil
- *      h.delete("z") { |el| "#{el} not found" }   #=> "z not found"
- *
- */
 static mrb_value
 mrb_hash_delete(mrb_state *mrb, mrb_value self)
 {
@@ -586,6 +1011,33 @@ mrb_hash_delete(mrb_state *mrb, mrb_value self)
   return mrb_hash_delete_key(mrb, self, key);
 }
 
+/* find first element in the hash table, and remove it. */
+static void
+ht_shift(mrb_state *mrb, htable *t, mrb_value *kp, mrb_value *vp)
+{
+  segment *seg = t->rootseg;
+  mrb_int i;
+
+  while (seg) {
+    for (i=0; i<seg->size; i++) {
+      mrb_value key;
+
+      if (!seg->next && i >= t->last_len) {
+        return;
+      }
+      key = seg->e[i].key;
+      if (mrb_undef_p(key)) continue;
+      *kp = key;
+      *vp = seg->e[i].val;
+      /* delete element */
+      seg->e[i].key = mrb_undef_value();
+      t->size--;
+      return;
+    }
+    seg = seg->next;
+  }
+}
+
 /* 15.2.13.4.24 */
 /*
  *  call-seq:
@@ -603,22 +1055,16 @@ mrb_hash_delete(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_hash_shift(mrb_state *mrb, mrb_value hash)
 {
-  khash_t(ht) *h = RHASH_TBL(hash);
-  khiter_t k;
-  mrb_value delKey, delVal;
+  htable *t = RHASH_TBL(hash);
 
   mrb_hash_modify(mrb, hash);
-  if (h && kh_size(h) > 0) {
-    for (k = kh_begin(h); k != kh_end(h); k++) {
-      if (!kh_exist(h, k)) continue;
-
-      delKey = kh_key(h, k);
-      mrb_gc_protect(mrb, delKey);
-      delVal = mrb_hash_delete_key(mrb, hash, delKey);
-      mrb_gc_protect(mrb, delVal);
+  if (t && t->size > 0) {
+    mrb_value del_key, del_val;
 
-      return mrb_assoc_new(mrb, delKey, delVal);
-    }
+    ht_shift(mrb, t, &del_key, &del_val);
+    mrb_gc_protect(mrb, del_key);
+    mrb_gc_protect(mrb, del_val);
+    return mrb_assoc_new(mrb, del_key, del_val);
   }
 
   if (MRB_RHASH_DEFAULT_P(hash)) {
@@ -647,10 +1093,13 @@ mrb_hash_shift(mrb_state *mrb, mrb_value hash)
 MRB_API mrb_value
 mrb_hash_clear(mrb_state *mrb, mrb_value hash)
 {
-  khash_t(ht) *h = RHASH_TBL(hash);
+  htable *t = RHASH_TBL(hash);
 
   mrb_hash_modify(mrb, hash);
-  if (h) kh_clear(ht, mrb, h);
+  if (t) {
+    ht_free(mrb, t);
+    RHASH_TBL(hash) = NULL;
+  }
   return hash;
 }
 
@@ -683,6 +1132,15 @@ mrb_hash_aset(mrb_state *mrb, mrb_value self)
   return val;
 }
 
+MRB_API mrb_int
+mrb_hash_size(mrb_state *mrb, mrb_value hash)
+{
+  htable *t = RHASH_TBL(hash);
+
+  if (!t) return 0;
+  return t->size;
+}
+
 /* 15.2.13.4.20 */
 /* 15.2.13.4.25 */
 /*
@@ -700,10 +1158,17 @@ mrb_hash_aset(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_hash_size_m(mrb_state *mrb, mrb_value self)
 {
-  khash_t(ht) *h = RHASH_TBL(self);
+  mrb_int size = mrb_hash_size(mrb, self);
+  return mrb_fixnum_value(size);
+}
+
+MRB_API mrb_bool
+mrb_hash_empty_p(mrb_state *mrb, mrb_value self)
+{
+  htable *t = RHASH_TBL(self);
 
-  if (!h) return mrb_fixnum_value(0);
-  return mrb_fixnum_value(kh_size(h));
+  if (!t) return TRUE;
+  return t->size == 0;
 }
 
 /* 15.2.13.4.12 */
@@ -716,27 +1181,17 @@ mrb_hash_size_m(mrb_state *mrb, mrb_value self)
  *     {}.empty?   #=> true
  *
  */
-MRB_API mrb_value
-mrb_hash_empty_p(mrb_state *mrb, mrb_value self)
+static mrb_value
+mrb_hash_empty_m(mrb_state *mrb, mrb_value self)
 {
-  khash_t(ht) *h = RHASH_TBL(self);
-
-  if (h) return mrb_bool_value(kh_size(h) == 0);
-  return mrb_true_value();
+  return mrb_bool_value(mrb_hash_empty_p(mrb, self));
 }
 
-/* 15.2.13.4.29 (x)*/
-/*
- * call-seq:
- *    hsh.to_hash   => hsh
- *
- * Returns +self+.
- */
-
-static mrb_value
-mrb_hash_to_hash(mrb_state *mrb, mrb_value hash)
+static int
+hash_keys_i(mrb_state *mrb, mrb_value key, mrb_value val, void *p)
 {
-  return hash;
+  mrb_ary_push(mrb, *(mrb_value*)p, key);
+  return 0;
 }
 
 /* 15.2.13.4.19 */
@@ -755,33 +1210,24 @@ mrb_hash_to_hash(mrb_state *mrb, mrb_value hash)
 MRB_API mrb_value
 mrb_hash_keys(mrb_state *mrb, mrb_value hash)
 {
-  khash_t(ht) *h = RHASH_TBL(hash);
-  khiter_t k;
-  mrb_int end;
+  htable *t = RHASH_TBL(hash);
+  mrb_int size;
   mrb_value ary;
-  mrb_value *p;
-
-  if (!h || kh_size(h) == 0) return mrb_ary_new(mrb);
-  ary = mrb_ary_new_capa(mrb, kh_size(h));
-  end = kh_size(h)-1;
-  mrb_ary_set(mrb, ary, end, mrb_nil_value());
-  p = RARRAY_PTR(ary);
-  for (k = kh_begin(h); k != kh_end(h); k++) {
-    if (kh_exist(h, k)) {
-      mrb_value kv = kh_key(h, k);
-      mrb_hash_value hv = kh_value(h, k);
-
-      if (hv.n <= end) {
-        p[hv.n] = kv;
-      }
-      else {
-        p[end] = kv;
-      }
-    }
-  }
+
+  if (!t || (size = t->size) == 0)
+    return mrb_ary_new(mrb);
+  ary = mrb_ary_new_capa(mrb, size);
+  ht_foreach(mrb, t, hash_keys_i, (void*)&ary);
   return ary;
 }
 
+static int
+hash_vals_i(mrb_state *mrb, mrb_value key, mrb_value val, void *p)
+{
+  mrb_ary_push(mrb, *(mrb_value*)p, val);
+  return 0;
+}
+
 /* 15.2.13.4.28 */
 /*
  *  call-seq:
@@ -798,19 +1244,14 @@ mrb_hash_keys(mrb_state *mrb, mrb_value hash)
 MRB_API mrb_value
 mrb_hash_values(mrb_state *mrb, mrb_value hash)
 {
-  khash_t(ht) *h = RHASH_TBL(hash);
-  khiter_t k;
+  htable *t = RHASH_TBL(hash);
+  mrb_int size;
   mrb_value ary;
 
-  if (!h) return mrb_ary_new(mrb);
-  ary = mrb_ary_new_capa(mrb, kh_size(h));
-  for (k = kh_begin(h); k != kh_end(h); k++) {
-    if (kh_exist(h, k)) {
-      mrb_hash_value hv = kh_value(h, k);
-
-      mrb_ary_set(mrb, ary, hv.n, hv.v);
-    }
-  }
+  if (!t || (size = t->size) == 0)
+    return mrb_ary_new(mrb);
+  ary = mrb_ary_new_capa(mrb, size);
+  ht_foreach(mrb, t, hash_vals_i, (void*)&ary);
   return ary;
 }
 
@@ -833,21 +1274,44 @@ mrb_hash_values(mrb_state *mrb, mrb_value hash)
  *
  */
 
+MRB_API mrb_bool
+mrb_hash_key_p(mrb_state *mrb, mrb_value hash, mrb_value key)
+{
+  htable *t;
+
+  t = RHASH_TBL(hash);
+  if (ht_get(mrb, t, key, NULL)) {
+    return TRUE;
+  }
+  return FALSE;
+}
+
 static mrb_value
 mrb_hash_has_key(mrb_state *mrb, mrb_value hash)
 {
   mrb_value key;
-  khash_t(ht) *h;
-  khiter_t k;
+  mrb_bool key_p;
 
   mrb_get_args(mrb, "o", &key);
+  key_p = mrb_hash_key_p(mrb, hash, key);
+  return mrb_bool_value(key_p);
+}
 
-  h = RHASH_TBL(hash);
-  if (h) {
-    k = kh_get(ht, mrb, h, key);
-    return mrb_bool_value(k != kh_end(h));
+struct has_v_arg {
+  mrb_bool found;
+  mrb_value val;
+};
+
+static int
+hash_has_value_i(mrb_state *mrb, mrb_value key, mrb_value val, void *p)
+{
+  struct has_v_arg *arg = (struct has_v_arg*)p;
+  
+  if (mrb_equal(mrb, arg->val, val)) {
+    arg->found = TRUE;
+    return 1;
   }
-  return mrb_false_value();
+  return 0;
 }
 
 /* 15.2.13.4.14 */
@@ -869,22 +1333,73 @@ static mrb_value
 mrb_hash_has_value(mrb_state *mrb, mrb_value hash)
 {
   mrb_value val;
-  khash_t(ht) *h;
-  khiter_t k;
-
+  struct has_v_arg arg;
+  
   mrb_get_args(mrb, "o", &val);
-  h = RHASH_TBL(hash);
+  arg.found = FALSE;
+  arg.val = val;
+  ht_foreach(mrb, RHASH_TBL(hash), hash_has_value_i, &arg);
+  return mrb_bool_value(arg.found);
+}
 
-  if (h) {
-    for (k = kh_begin(h); k != kh_end(h); k++) {
-      if (!kh_exist(h, k)) continue;
+static int
+merge_i(mrb_state *mrb, mrb_value key, mrb_value val, void *data)
+{
+  htable *h1 = (htable*)data;
 
-      if (mrb_equal(mrb, kh_value(h, k).v, val)) {
-        return mrb_true_value();
-      }
-    }
+  ht_put(mrb, h1, key, val);
+  return 0;
+}
+
+MRB_API void
+mrb_hash_merge(mrb_state *mrb, mrb_value hash1, mrb_value hash2)
+{
+  htable *h1, *h2;
+
+  mrb_hash_modify(mrb, hash1);
+  hash2 = mrb_ensure_hash_type(mrb, hash2);
+  h1 = RHASH_TBL(hash1);
+  h2 = RHASH_TBL(hash2);
+
+  if (!h2) return;
+  if (!h1) {
+    RHASH_TBL(hash1) = ht_copy(mrb, h2);
+    return;
   }
-  return mrb_false_value();
+  ht_foreach(mrb, h2, merge_i, h1);
+  mrb_write_barrier(mrb, (struct RBasic*)RHASH(hash1));
+  return;
+}
+
+/*
+ *  call-seq:
+ *    hsh.rehash -> hsh
+ *
+ *  Rebuilds the hash based on the current hash values for each key. If
+ *  values of key objects have changed since they were inserted, this
+ *  method will reindex <i>hsh</i>.
+ *
+ *     keys = (1..17).map{|n| [n]}
+ *     k = keys[0]
+ *     h = {}
+ *     keys.each{|key| h[key] = key[0]}
+ *     h     #=> { [1]=> 1, [2]=> 2, [3]=> 3, [4]=> 4, [5]=> 5, [6]=> 6, [7]=> 7,
+ *                 [8]=> 8, [9]=> 9,[10]=>10,[11]=>11,[12]=>12,[13]=>13,[14]=>14,
+ *                [15]=>15,[16]=>16,[17]=>17}
+ *     h[k]  #=> 1
+ *     k[0] = keys.size + 1
+ *     h     #=> {[18]=> 1, [2]=> 2, [3]=> 3, [4]=> 4, [5]=> 5, [6]=> 6, [7]=> 7,
+ *                 [8]=> 8, [9]=> 9,[10]=>10,[11]=>11,[12]=>12,[13]=>13,[14]=>14,
+ *                [15]=>15,[16]=>16,[17]=>17}
+ *     h[k]  #=> nil
+ *     h.rehash
+ *     h[k]  #=> 1
+ */
+static mrb_value
+mrb_hash_rehash(mrb_state *mrb, mrb_value self)
+{
+  ht_compact(mrb, RHASH_TBL(self));
+  return self;
 }
 
 void
@@ -904,7 +1419,7 @@ mrb_init_hash(mrb_state *mrb)
   mrb_define_method(mrb, h, "default_proc",    mrb_hash_default_proc,MRB_ARGS_NONE()); /* 15.2.13.4.7  */
   mrb_define_method(mrb, h, "default_proc=",   mrb_hash_set_default_proc,MRB_ARGS_REQ(1)); /* 15.2.13.4.7  */
   mrb_define_method(mrb, h, "__delete",        mrb_hash_delete,      MRB_ARGS_REQ(1)); /* core of 15.2.13.4.8  */
-  mrb_define_method(mrb, h, "empty?",          mrb_hash_empty_p,     MRB_ARGS_NONE()); /* 15.2.13.4.12 */
+  mrb_define_method(mrb, h, "empty?",          mrb_hash_empty_m,     MRB_ARGS_NONE()); /* 15.2.13.4.12 */
   mrb_define_method(mrb, h, "has_key?",        mrb_hash_has_key,     MRB_ARGS_REQ(1)); /* 15.2.13.4.13 */
   mrb_define_method(mrb, h, "has_value?",      mrb_hash_has_value,   MRB_ARGS_REQ(1)); /* 15.2.13.4.14 */
   mrb_define_method(mrb, h, "include?",        mrb_hash_has_key,     MRB_ARGS_REQ(1)); /* 15.2.13.4.15 */
@@ -918,6 +1433,5 @@ mrb_init_hash(mrb_state *mrb)
   mrb_define_method(mrb, h, "store",           mrb_hash_aset,        MRB_ARGS_REQ(2)); /* 15.2.13.4.26 */
   mrb_define_method(mrb, h, "value?",          mrb_hash_has_value,   MRB_ARGS_REQ(1)); /* 15.2.13.4.27 */
   mrb_define_method(mrb, h, "values",          mrb_hash_values,      MRB_ARGS_NONE()); /* 15.2.13.4.28 */
-
-  mrb_define_method(mrb, h, "to_hash",         mrb_hash_to_hash,     MRB_ARGS_NONE()); /* 15.2.13.4.29 (x)*/
+  mrb_define_method(mrb, h, "rehash",          mrb_hash_rehash,      MRB_ARGS_NONE());
 }
diff --git a/src/kernel.c b/src/kernel.c
index f378004cb..a3c2d2ec6 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -14,24 +14,11 @@
 #include <mruby/error.h>
 #include <mruby/istruct.h>
 
-typedef enum {
-  NOEX_PUBLIC    = 0x00,
-  NOEX_NOSUPER   = 0x01,
-  NOEX_PRIVATE   = 0x02,
-  NOEX_PROTECTED = 0x04,
-  NOEX_MASK      = 0x06,
-  NOEX_BASIC     = 0x08,
-  NOEX_UNDEF     = NOEX_NOSUPER,
-  NOEX_MODFUNC   = 0x12,
-  NOEX_SUPER     = 0x20,
-  NOEX_VCALL     = 0x40,
-  NOEX_RESPONDS  = 0x80
-} mrb_method_flag_t;
-
 MRB_API mrb_bool
 mrb_func_basic_p(mrb_state *mrb, mrb_value obj, mrb_sym mid, mrb_func_t func)
 {
-  mrb_method_t m = mrb_method_search(mrb, mrb_class(mrb, obj), mid);
+  struct RClass *c = mrb_class(mrb, obj);
+  mrb_method_t m = mrb_method_search_vm(mrb, &c, mid);
   struct RProc *p;
 
   if (MRB_METHOD_UNDEF_P(m)) return FALSE;
@@ -252,18 +239,18 @@ copy_class(mrb_state *mrb, mrb_value dst, mrb_value src)
   struct RClass *sc = mrb_class_ptr(src);
   /* if the origin is not the same as the class, then the origin and
      the current class need to be copied */
-  if (sc->flags & MRB_FLAG_IS_PREPENDED) {
+  if (sc->flags & MRB_FL_CLASS_IS_PREPENDED) {
     struct RClass *c0 = sc->super;
     struct RClass *c1 = dc;
 
     /* copy prepended iclasses */
-    while (!(c0->flags & MRB_FLAG_IS_ORIGIN)) {
+    while (!(c0->flags & MRB_FL_CLASS_IS_ORIGIN)) {
       c1->super = mrb_class_ptr(mrb_obj_dup(mrb, mrb_obj_value(c0)));
       c1 = c1->super;
       c0 = c0->super;
     }
     c1->super = mrb_class_ptr(mrb_obj_dup(mrb, mrb_obj_value(c0)));
-    c1->super->flags |= MRB_FLAG_IS_ORIGIN;
+    c1->super->flags |= MRB_FL_CLASS_IS_ORIGIN;
   }
   if (sc->mt) {
     dc->mt = kh_copy(mt, mrb, sc->mt);
@@ -348,7 +335,7 @@ mrb_obj_clone(mrb_state *mrb, mrb_value self)
   mrb_field_write_barrier(mrb, (struct RBasic*)p, (struct RBasic*)p->c);
   clone = mrb_obj_value(p);
   init_copy(mrb, clone, self);
-  p->flags = mrb_obj_ptr(self)->flags;
+  p->flags |= mrb_obj_ptr(self)->flags & MRB_FL_OBJ_IS_FROZEN;
 
   return clone;
 }
@@ -447,24 +434,12 @@ mrb_obj_extend_m(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_obj_freeze(mrb_state *mrb, mrb_value self)
 {
-  struct RBasic *b;
-
-  switch (mrb_type(self)) {
-    case MRB_TT_FALSE:
-    case MRB_TT_TRUE:
-    case MRB_TT_FIXNUM:
-    case MRB_TT_SYMBOL:
-#ifndef MRB_WITHOUT_FLOAT
-    case MRB_TT_FLOAT:
-#endif
-      return self;
-    default:
-      break;
-  }
-
-  b = mrb_basic_ptr(self);
-  if (!MRB_FROZEN_P(b)) {
-    MRB_SET_FROZEN_FLAG(b);
+  if (!mrb_immediate_p(self)) {
+    struct RBasic *b = mrb_basic_ptr(self);
+    if (!MRB_FROZEN_P(b)) {
+      MRB_SET_FROZEN_FLAG(b);
+      if (b->c->tt == MRB_TT_SCLASS) MRB_SET_FROZEN_FLAG(b->c);
+    }
   }
   return self;
 }
@@ -472,26 +447,7 @@ mrb_obj_freeze(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_obj_frozen(mrb_state *mrb, mrb_value self)
 {
-  struct RBasic *b;
-
-  switch (mrb_type(self)) {
-    case MRB_TT_FALSE:
-    case MRB_TT_TRUE:
-    case MRB_TT_FIXNUM:
-    case MRB_TT_SYMBOL:
-#ifndef MRB_WITHOUT_FLOAT
-    case MRB_TT_FLOAT:
-#endif
-      return mrb_true_value();
-    default:
-      break;
-  }
-
-  b = mrb_basic_ptr(self);
-  if (!MRB_FROZEN_P(b)) {
-    return mrb_false_value();
-  }
-  return mrb_true_value();
+  return mrb_bool_value(mrb_immediate_p(self) || MRB_FROZEN_P(mrb_basic_ptr(self)));
 }
 
 /* 15.3.1.3.15 */
@@ -505,7 +461,7 @@ mrb_obj_frozen(mrb_state *mrb, mrb_value self)
  *  <code>Hash</code>. Any hash value that exceeds the capacity of a
  *  <code>Fixnum</code> will be truncated before being used.
  */
-MRB_API mrb_value
+static mrb_value
 mrb_obj_hash(mrb_state *mrb, mrb_value self)
 {
   return mrb_fixnum_value(mrb_obj_id(self));
@@ -551,96 +507,6 @@ obj_is_instance_of(mrb_state *mrb, mrb_value self)
   return mrb_bool_value(mrb_obj_is_instance_of(mrb, self, mrb_class_ptr(arg)));
 }
 
-/* 15.3.1.3.20 */
-/*
- *  call-seq:
- *     obj.instance_variable_defined?(symbol)    -> true or false
- *
- *  Returns <code>true</code> if the given instance variable is
- *  defined in <i>obj</i>.
- *
- *     class Fred
- *       def initialize(p1, p2)
- *         @a, @b = p1, p2
- *       end
- *     end
- *     fred = Fred.new('cat', 99)
- *     fred.instance_variable_defined?(:@a)    #=> true
- *     fred.instance_variable_defined?("@b")   #=> true
- *     fred.instance_variable_defined?("@c")   #=> false
- */
-static mrb_value
-mrb_obj_ivar_defined(mrb_state *mrb, mrb_value self)
-{
-  mrb_sym sym;
-
-  mrb_get_args(mrb, "n", &sym);
-  mrb_iv_check(mrb, sym);
-  return mrb_bool_value(mrb_iv_defined(mrb, self, sym));
-}
-
-/* 15.3.1.3.21 */
-/*
- *  call-seq:
- *     obj.instance_variable_get(symbol)    -> obj
- *
- *  Returns the value of the given instance variable, or nil if the
- *  instance variable is not set. The <code>@</code> part of the
- *  variable name should be included for regular instance
- *  variables. Throws a <code>NameError</code> exception if the
- *  supplied symbol is not valid as an instance variable name.
- *
- *     class Fred
- *       def initialize(p1, p2)
- *         @a, @b = p1, p2
- *       end
- *     end
- *     fred = Fred.new('cat', 99)
- *     fred.instance_variable_get(:@a)    #=> "cat"
- *     fred.instance_variable_get("@b")   #=> 99
- */
-static mrb_value
-mrb_obj_ivar_get(mrb_state *mrb, mrb_value self)
-{
-  mrb_sym iv_name;
-
-  mrb_get_args(mrb, "n", &iv_name);
-  mrb_iv_check(mrb, iv_name);
-  return mrb_iv_get(mrb, self, iv_name);
-}
-
-/* 15.3.1.3.22 */
-/*
- *  call-seq:
- *     obj.instance_variable_set(symbol, obj)    -> obj
- *
- *  Sets the instance variable names by <i>symbol</i> to
- *  <i>object</i>, thereby frustrating the efforts of the class's
- *  author to attempt to provide proper encapsulation. The variable
- *  did not have to exist prior to this call.
- *
- *     class Fred
- *       def initialize(p1, p2)
- *         @a, @b = p1, p2
- *       end
- *     end
- *     fred = Fred.new('cat', 99)
- *     fred.instance_variable_set(:@a, 'dog')   #=> "dog"
- *     fred.instance_variable_set(:@c, 'cat')   #=> "cat"
- *     fred.inspect                             #=> "#<Fred:0x401b3da8 @a=\"dog\", @b=99, @c=\"cat\">"
- */
-static mrb_value
-mrb_obj_ivar_set(mrb_state *mrb, mrb_value self)
-{
-  mrb_sym iv_name;
-  mrb_value val;
-
-  mrb_get_args(mrb, "no", &iv_name, &val);
-  mrb_iv_check(mrb, iv_name);
-  mrb_iv_set(mrb, self, iv_name, val);
-  return val;
-}
-
 /* 15.3.1.3.24 */
 /* 15.3.1.3.26 */
 /*
@@ -681,124 +547,6 @@ mrb_obj_is_kind_of_m(mrb_state *mrb, mrb_value self)
 KHASH_DECLARE(st, mrb_sym, char, FALSE)
 KHASH_DEFINE(st, mrb_sym, char, FALSE, kh_int_hash_func, kh_int_hash_equal)
 
-static void
-method_entry_loop(mrb_state *mrb, struct RClass* klass, khash_t(st)* set)
-{
-  khint_t i;
-
-  khash_t(mt) *h = klass->mt;
-  if (!h || kh_size(h) == 0) return;
-  for (i=0;i<kh_end(h);i++) {
-    if (kh_exist(h, i)) {
-      mrb_method_t m = kh_value(h, i);
-      if (MRB_METHOD_UNDEF_P(m)) continue;
-      kh_put(st, mrb, set, kh_key(h, i));
-    }
-  }
-}
-
-mrb_value
-mrb_class_instance_method_list(mrb_state *mrb, mrb_bool recur, struct RClass* klass, int obj)
-{
-  khint_t i;
-  mrb_value ary;
-  mrb_bool prepended = FALSE;
-  struct RClass* oldklass;
-  khash_t(st)* set = kh_init(st, mrb);
-
-  if (!recur && (klass->flags & MRB_FLAG_IS_PREPENDED)) {
-    MRB_CLASS_ORIGIN(klass);
-    prepended = TRUE;
-  }
-
-  oldklass = 0;
-  while (klass && (klass != oldklass)) {
-    method_entry_loop(mrb, klass, set);
-    if ((klass->tt == MRB_TT_ICLASS && !prepended) ||
-        (klass->tt == MRB_TT_SCLASS)) {
-    }
-    else {
-      if (!recur) break;
-    }
-    oldklass = klass;
-    klass = klass->super;
-  }
-
-  ary = mrb_ary_new_capa(mrb, kh_size(set));
-  for (i=0;i<kh_end(set);i++) {
-    if (kh_exist(set, i)) {
-      mrb_ary_push(mrb, ary, mrb_symbol_value(kh_key(set, i)));
-    }
-  }
-  kh_destroy(st, mrb, set);
-
-  return ary;
-}
-
-static mrb_value
-mrb_obj_singleton_methods(mrb_state *mrb, mrb_bool recur, mrb_value obj)
-{
-  khint_t i;
-  mrb_value ary;
-  struct RClass* klass;
-  khash_t(st)* set = kh_init(st, mrb);
-
-  klass = mrb_class(mrb, obj);
-
-  if (klass && (klass->tt == MRB_TT_SCLASS)) {
-      method_entry_loop(mrb, klass, set);
-      klass = klass->super;
-  }
-  if (recur) {
-      while (klass && ((klass->tt == MRB_TT_SCLASS) || (klass->tt == MRB_TT_ICLASS))) {
-        method_entry_loop(mrb, klass, set);
-        klass = klass->super;
-      }
-  }
-
-  ary = mrb_ary_new(mrb);
-  for (i=0;i<kh_end(set);i++) {
-    if (kh_exist(set, i)) {
-      mrb_ary_push(mrb, ary, mrb_symbol_value(kh_key(set, i)));
-    }
-  }
-  kh_destroy(st, mrb, set);
-
-  return ary;
-}
-
-static mrb_value
-mrb_obj_methods(mrb_state *mrb, mrb_bool recur, mrb_value obj, mrb_method_flag_t flag)
-{
-  return mrb_class_instance_method_list(mrb, recur, mrb_class(mrb, obj), 0);
-}
-/* 15.3.1.3.31 */
-/*
- *  call-seq:
- *     obj.methods    -> array
- *
- *  Returns a list of the names of methods publicly accessible in
- *  <i>obj</i>. This will include all the methods accessible in
- *  <i>obj</i>'s ancestors.
- *
- *     class Klass
- *       def kMethod()
- *       end
- *     end
- *     k = Klass.new
- *     k.methods[0..9]    #=> [:kMethod, :respond_to?, :nil?, :is_a?,
- *                        #    :class, :instance_variable_set,
- *                        #    :methods, :extend, :__send__, :instance_eval]
- *     k.methods.length   #=> 42
- */
-static mrb_value
-mrb_obj_methods_m(mrb_state *mrb, mrb_value self)
-{
-  mrb_bool recur = TRUE;
-  mrb_get_args(mrb, "|b", &recur);
-  return mrb_obj_methods(mrb, recur, self, (mrb_method_flag_t)0); /* everything but private */
-}
-
 /* 15.3.1.3.32 */
 /*
  * call_seq:
@@ -813,57 +561,6 @@ mrb_false(mrb_state *mrb, mrb_value self)
   return mrb_false_value();
 }
 
-/* 15.3.1.3.36 */
-/*
- *  call-seq:
- *     obj.private_methods(all=true)   -> array
- *
- *  Returns the list of private methods accessible to <i>obj</i>. If
- *  the <i>all</i> parameter is set to <code>false</code>, only those methods
- *  in the receiver will be listed.
- */
-static mrb_value
-mrb_obj_private_methods(mrb_state *mrb, mrb_value self)
-{
-  mrb_bool recur = TRUE;
-  mrb_get_args(mrb, "|b", &recur);
-  return mrb_obj_methods(mrb, recur, self, NOEX_PRIVATE); /* private attribute not define */
-}
-
-/* 15.3.1.3.37 */
-/*
- *  call-seq:
- *     obj.protected_methods(all=true)   -> array
- *
- *  Returns the list of protected methods accessible to <i>obj</i>. If
- *  the <i>all</i> parameter is set to <code>false</code>, only those methods
- *  in the receiver will be listed.
- */
-static mrb_value
-mrb_obj_protected_methods(mrb_state *mrb, mrb_value self)
-{
-  mrb_bool recur = TRUE;
-  mrb_get_args(mrb, "|b", &recur);
-  return mrb_obj_methods(mrb, recur, self, NOEX_PROTECTED); /* protected attribute not define */
-}
-
-/* 15.3.1.3.38 */
-/*
- *  call-seq:
- *     obj.public_methods(all=true)   -> array
- *
- *  Returns the list of public methods accessible to <i>obj</i>. If
- *  the <i>all</i> parameter is set to <code>false</code>, only those methods
- *  in the receiver will be listed.
- */
-static mrb_value
-mrb_obj_public_methods(mrb_state *mrb, mrb_value self)
-{
-  mrb_bool recur = TRUE;
-  mrb_get_args(mrb, "|b", &recur);
-  return mrb_obj_methods(mrb, recur, self, NOEX_PUBLIC); /* public attribute not define */
-}
-
 /* 15.3.1.2.12  */
 /* 15.3.1.3.40 */
 /*
@@ -912,16 +609,6 @@ mrb_f_raise(mrb_state *mrb, mrb_value self)
   return mrb_nil_value();            /* not reached */
 }
 
-static mrb_value
-mrb_krn_class_defined(mrb_state *mrb, mrb_value self)
-{
-  mrb_value str;
-
-  mrb_get_args(mrb, "S", &str);
-  return mrb_bool_value(mrb_class_defined(mrb, RSTRING_PTR(str)));
-}
-
-
 /* 15.3.1.3.41 */
 /*
  *  call-seq:
@@ -951,7 +638,7 @@ mrb_obj_remove_instance_variable(mrb_state *mrb, mrb_value self)
   mrb_value val;
 
   mrb_get_args(mrb, "n", &sym);
-  mrb_iv_check(mrb, sym);
+  mrb_iv_name_sym_check(mrb, sym);
   val = mrb_iv_remove(mrb, self, sym);
   if (mrb_undef_p(val)) {
     mrb_name_error(mrb, sym, "instance variable %S not defined", mrb_sym2str(mrb, sym));
@@ -1018,6 +705,7 @@ basic_obj_respond_to(mrb_state *mrb, mrb_value obj, mrb_sym id, int pub)
 {
   return mrb_respond_to(mrb, obj, id);
 }
+
 /* 15.3.1.3.43 */
 /*
  *  call-seq:
@@ -1037,45 +725,16 @@ basic_obj_respond_to(mrb_state *mrb, mrb_value obj, mrb_sym id, int pub)
 static mrb_value
 obj_respond_to(mrb_state *mrb, mrb_value self)
 {
-  mrb_value mid;
   mrb_sym id, rtm_id;
-  mrb_bool priv = FALSE, respond_to_p = TRUE;
-
-  mrb_get_args(mrb, "o|b", &mid, &priv);
-
-  if (mrb_symbol_p(mid)) {
-    id = mrb_symbol(mid);
-  }
-  else {
-    mrb_value tmp;
-    if (mrb_string_p(mid)) {
-      tmp = mrb_check_intern_str(mrb, mid);
-    }
-    else {
-      tmp = mrb_check_string_type(mrb, mid);
-      if (mrb_nil_p(tmp)) {
-        tmp = mrb_inspect(mrb, mid);
-        mrb_raisef(mrb, E_TYPE_ERROR, "%S is not a symbol", tmp);
-      }
-      tmp = mrb_check_intern_str(mrb, tmp);
-    }
-    if (mrb_nil_p(tmp)) {
-      respond_to_p = FALSE;
-    }
-    else {
-      id = mrb_symbol(tmp);
-    }
-  }
-
-  if (respond_to_p) {
-    respond_to_p = basic_obj_respond_to(mrb, self, id, !priv);
-  }
+  mrb_bool priv = FALSE, respond_to_p;
 
+  mrb_get_args(mrb, "n|b", &id, &priv);
+  respond_to_p = basic_obj_respond_to(mrb, self, id, !priv);
   if (!respond_to_p) {
     rtm_id = mrb_intern_lit(mrb, "respond_to_missing?");
     if (basic_obj_respond_to(mrb, self, rtm_id, !priv)) {
       mrb_value args[2], v;
-      args[0] = mid;
+      args[0] = mrb_symbol_value(id);
       args[1] = mrb_bool_value(priv);
       v = mrb_funcall_argv(mrb, self, rtm_id, 2, args);
       return mrb_bool_value(mrb_bool(v));
@@ -1084,67 +743,6 @@ obj_respond_to(mrb_state *mrb, mrb_value self)
   return mrb_bool_value(respond_to_p);
 }
 
-/* 15.3.1.3.45 */
-/*
- *  call-seq:
- *     obj.singleton_methods(all=true)    -> array
- *
- *  Returns an array of the names of singleton methods for <i>obj</i>.
- *  If the optional <i>all</i> parameter is true, the list will include
- *  methods in modules included in <i>obj</i>.
- *  Only public and protected singleton methods are returned.
- *
- *     module Other
- *       def three() end
- *     end
- *
- *     class Single
- *       def Single.four() end
- *     end
- *
- *     a = Single.new
- *
- *     def a.one()
- *     end
- *
- *     class << a
- *       include Other
- *       def two()
- *       end
- *     end
- *
- *     Single.singleton_methods    #=> [:four]
- *     a.singleton_methods(false)  #=> [:two, :one]
- *     a.singleton_methods         #=> [:two, :one, :three]
- */
-static mrb_value
-mrb_obj_singleton_methods_m(mrb_state *mrb, mrb_value self)
-{
-  mrb_bool recur = TRUE;
-  mrb_get_args(mrb, "|b", &recur);
-  return mrb_obj_singleton_methods(mrb, recur, self);
-}
-
-static mrb_value
-mod_define_singleton_method(mrb_state *mrb, mrb_value self)
-{
-  struct RProc *p;
-  mrb_method_t m;
-  mrb_sym mid;
-  mrb_value blk = mrb_nil_value();
-
-  mrb_get_args(mrb, "n&", &mid, &blk);
-  if (mrb_nil_p(blk)) {
-    mrb_raise(mrb, E_ARGUMENT_ERROR, "no block given");
-  }
-  p = (struct RProc*)mrb_obj_alloc(mrb, MRB_TT_PROC, mrb->proc_class);
-  mrb_proc_copy(p, mrb_proc_ptr(blk));
-  p->flags |= MRB_PROC_STRICT;
-  MRB_METHOD_FROM_PROC(m, p);
-  mrb_define_method_raw(mrb, mrb_class_ptr(mrb_singleton_class(mrb, self)), mid, m);
-  return mrb_symbol_value(mid);
-}
-
 static mrb_value
 mrb_obj_ceqq(mrb_state *mrb, mrb_value self)
 {
@@ -1162,51 +760,8 @@ mrb_obj_ceqq(mrb_state *mrb, mrb_value self)
   return mrb_false_value();
 }
 
-/* 15.3.1.2.7 */
-/*
- *  call-seq:
- *     local_variables   -> array
- *
- *  Returns the names of local variables in the current scope.
- *
- *  [mruby limitation]
- *  If variable symbol information was stripped out from
- *  compiled binary files using `mruby-strip -l`, this
- *  method always returns an empty array.
- */
-static mrb_value
-mrb_local_variables(mrb_state *mrb, mrb_value self)
-{
-  struct RProc *proc;
-  mrb_irep *irep;
-  mrb_value vars;
-  size_t i;
-
-  proc = mrb->c->ci[-1].proc;
-
-  if (MRB_PROC_CFUNC_P(proc)) {
-    return mrb_ary_new(mrb);
-  }
-  vars = mrb_hash_new(mrb);
-  while (proc) {
-    if (MRB_PROC_CFUNC_P(proc)) break;
-    irep = proc->body.irep;
-    if (!irep->lv) break;
-    for (i = 0; i + 1 < irep->nlocals; ++i) {
-      if (irep->lv[i].name) {
-        mrb_hash_set(mrb, vars, mrb_symbol_value(irep->lv[i].name), mrb_true_value());
-      }
-    }
-    if (!MRB_PROC_ENV_P(proc)) break;
-    proc = proc->upper;
-    //if (MRB_PROC_SCOPE_P(proc)) break;
-    if (!proc->c) break;
-  }
-
-  return mrb_hash_keys(mrb, vars);
-}
-
 mrb_value mrb_obj_equal_m(mrb_state *mrb, mrb_value);
+
 void
 mrb_init_kernel(mrb_state *mrb)
 {
@@ -1214,13 +769,10 @@ mrb_init_kernel(mrb_state *mrb)
 
   mrb->kernel_module = krn = mrb_define_module(mrb, "Kernel");                                                    /* 15.3.1 */
   mrb_define_class_method(mrb, krn, "block_given?",         mrb_f_block_given_p_m,           MRB_ARGS_NONE());    /* 15.3.1.2.2  */
-  mrb_define_class_method(mrb, krn, "global_variables",     mrb_f_global_variables,          MRB_ARGS_NONE());    /* 15.3.1.2.4  */
   mrb_define_class_method(mrb, krn, "iterator?",            mrb_f_block_given_p_m,           MRB_ARGS_NONE());    /* 15.3.1.2.5  */
-  mrb_define_class_method(mrb, krn, "local_variables",      mrb_local_variables,             MRB_ARGS_NONE());    /* 15.3.1.2.7  */
 ;     /* 15.3.1.2.11 */
   mrb_define_class_method(mrb, krn, "raise",                mrb_f_raise,                     MRB_ARGS_OPT(2));    /* 15.3.1.2.12 */
 
-  mrb_define_method(mrb, krn, "singleton_class",            mrb_singleton_class,             MRB_ARGS_NONE());
 
   mrb_define_method(mrb, krn, "===",                        mrb_equal_m,                     MRB_ARGS_REQ(1));    /* 15.3.1.3.2  */
   mrb_define_method(mrb, krn, "block_given?",               mrb_f_block_given_p_m,           MRB_ARGS_NONE());    /* 15.3.1.3.6  */
@@ -1228,43 +780,30 @@ mrb_init_kernel(mrb_state *mrb)
   mrb_define_method(mrb, krn, "clone",                      mrb_obj_clone,                   MRB_ARGS_NONE());    /* 15.3.1.3.8  */
   mrb_define_method(mrb, krn, "dup",                        mrb_obj_dup,                     MRB_ARGS_NONE());    /* 15.3.1.3.9  */
   mrb_define_method(mrb, krn, "eql?",                       mrb_obj_equal_m,                 MRB_ARGS_REQ(1));    /* 15.3.1.3.10 */
-  mrb_define_method(mrb, krn, "equal?",                     mrb_obj_equal_m,                 MRB_ARGS_REQ(1));    /* 15.3.1.3.11 */
   mrb_define_method(mrb, krn, "extend",                     mrb_obj_extend_m,                MRB_ARGS_ANY());     /* 15.3.1.3.13 */
   mrb_define_method(mrb, krn, "freeze",                     mrb_obj_freeze,                  MRB_ARGS_NONE());
   mrb_define_method(mrb, krn, "frozen?",                    mrb_obj_frozen,                  MRB_ARGS_NONE());
-  mrb_define_method(mrb, krn, "global_variables",           mrb_f_global_variables,          MRB_ARGS_NONE());    /* 15.3.1.3.14 */
   mrb_define_method(mrb, krn, "hash",                       mrb_obj_hash,                    MRB_ARGS_NONE());    /* 15.3.1.3.15 */
   mrb_define_method(mrb, krn, "initialize_copy",            mrb_obj_init_copy,               MRB_ARGS_REQ(1));    /* 15.3.1.3.16 */
   mrb_define_method(mrb, krn, "inspect",                    mrb_obj_inspect,                 MRB_ARGS_NONE());    /* 15.3.1.3.17 */
   mrb_define_method(mrb, krn, "instance_of?",               obj_is_instance_of,              MRB_ARGS_REQ(1));    /* 15.3.1.3.19 */
-  mrb_define_method(mrb, krn, "instance_variable_defined?", mrb_obj_ivar_defined,            MRB_ARGS_REQ(1));    /* 15.3.1.3.20 */
-  mrb_define_method(mrb, krn, "instance_variable_get",      mrb_obj_ivar_get,                MRB_ARGS_REQ(1));    /* 15.3.1.3.21 */
-  mrb_define_method(mrb, krn, "instance_variable_set",      mrb_obj_ivar_set,                MRB_ARGS_REQ(2));    /* 15.3.1.3.22 */
-  mrb_define_method(mrb, krn, "instance_variables",         mrb_obj_instance_variables,      MRB_ARGS_NONE());    /* 15.3.1.3.23 */
+
   mrb_define_method(mrb, krn, "is_a?",                      mrb_obj_is_kind_of_m,            MRB_ARGS_REQ(1));    /* 15.3.1.3.24 */
   mrb_define_method(mrb, krn, "iterator?",                  mrb_f_block_given_p_m,           MRB_ARGS_NONE());    /* 15.3.1.3.25 */
   mrb_define_method(mrb, krn, "kind_of?",                   mrb_obj_is_kind_of_m,            MRB_ARGS_REQ(1));    /* 15.3.1.3.26 */
-  mrb_define_method(mrb, krn, "local_variables",            mrb_local_variables,             MRB_ARGS_NONE());    /* 15.3.1.3.28 */
 #ifdef MRB_DEFAULT_METHOD_MISSING
   mrb_define_method(mrb, krn, "method_missing",             mrb_obj_missing,                 MRB_ARGS_ANY());     /* 15.3.1.3.30 */
 #endif
-  mrb_define_method(mrb, krn, "methods",                    mrb_obj_methods_m,               MRB_ARGS_OPT(1));    /* 15.3.1.3.31 */
   mrb_define_method(mrb, krn, "nil?",                       mrb_false,                       MRB_ARGS_NONE());    /* 15.3.1.3.32 */
   mrb_define_method(mrb, krn, "object_id",                  mrb_obj_id_m,                    MRB_ARGS_NONE());    /* 15.3.1.3.33 */
-  mrb_define_method(mrb, krn, "private_methods",            mrb_obj_private_methods,         MRB_ARGS_OPT(1));    /* 15.3.1.3.36 */
-  mrb_define_method(mrb, krn, "protected_methods",          mrb_obj_protected_methods,       MRB_ARGS_OPT(1));    /* 15.3.1.3.37 */
-  mrb_define_method(mrb, krn, "public_methods",             mrb_obj_public_methods,          MRB_ARGS_OPT(1));    /* 15.3.1.3.38 */
   mrb_define_method(mrb, krn, "raise",                      mrb_f_raise,                     MRB_ARGS_ANY());     /* 15.3.1.3.40 */
   mrb_define_method(mrb, krn, "remove_instance_variable",   mrb_obj_remove_instance_variable,MRB_ARGS_REQ(1));    /* 15.3.1.3.41 */
   mrb_define_method(mrb, krn, "respond_to?",                obj_respond_to,                  MRB_ARGS_ANY());     /* 15.3.1.3.43 */
-  mrb_define_method(mrb, krn, "send",                       mrb_f_send,                      MRB_ARGS_ANY());     /* 15.3.1.3.44 */
-  mrb_define_method(mrb, krn, "singleton_methods",          mrb_obj_singleton_methods_m,     MRB_ARGS_OPT(1));    /* 15.3.1.3.45 */
-  mrb_define_method(mrb, krn, "define_singleton_method",    mod_define_singleton_method,     MRB_ARGS_ANY());
   mrb_define_method(mrb, krn, "to_s",                       mrb_any_to_s,                    MRB_ARGS_NONE());    /* 15.3.1.3.46 */
   mrb_define_method(mrb, krn, "__case_eqq",                 mrb_obj_ceqq,                    MRB_ARGS_REQ(1));    /* internal */
-
-  mrb_define_method(mrb, krn, "class_defined?",             mrb_krn_class_defined,           MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, krn, "__to_int",                   mrb_to_int,                      MRB_ARGS_NONE()); /* internal */
+  mrb_define_method(mrb, krn, "__to_str",                   mrb_to_str,                      MRB_ARGS_NONE()); /* internal */
 
   mrb_include_module(mrb, mrb->object_class, mrb->kernel_module);
-  mrb_alias_method(mrb, mrb->module_class, mrb_intern_lit(mrb, "dup"), mrb_intern_lit(mrb, "clone"));
+  mrb_define_alias(mrb, mrb->module_class, "dup", "clone"); /* XXX */
 }
diff --git a/src/load.c b/src/load.c
index ddf3cdfbf..97eafdbb5 100644
--- a/src/load.c
+++ b/src/load.c
@@ -7,6 +7,7 @@
 #include <limits.h>
 #include <stdlib.h>
 #include <string.h>
+#include <math.h>
 #include <mruby/dump.h>
 #include <mruby/irep.h>
 #include <mruby/proc.h>
@@ -40,6 +41,23 @@ offset_crc_body(void)
   return ((uint8_t *)header.binary_crc - (uint8_t *)&header) + sizeof(header.binary_crc);
 }
 
+#ifndef MRB_WITHOUT_FLOAT
+static double
+str_to_double(mrb_state *mrb, mrb_value str)
+{
+  const char *p = RSTRING_PTR(str);
+  mrb_int len = RSTRING_LEN(str);
+
+  /* `i`, `inf`, `infinity` */
+  if (len > 0 && p[0] == 'i') return INFINITY;
+
+  /* `I`, `-inf`, `-infinity` */
+  if (p[0] == 'I' || (len > 1 && p[0] == '-' && p[1] == 'i')) return -INFINITY;
+
+  return mrb_str_to_dbl(mrb, str, TRUE);
+}
+#endif
+
 static mrb_irep*
 read_irep_record_1(mrb_state *mrb, const uint8_t *bin, size_t *len, uint8_t flags)
 {
@@ -68,7 +86,7 @@ read_irep_record_1(mrb_state *mrb, const uint8_t *bin, size_t *len, uint8_t flag
 
   /* Binary Data Section */
   /* ISEQ BLOCK */
-  irep->ilen = (size_t)bin_to_uint32(src);
+  irep->ilen = (uint16_t)bin_to_uint32(src);
   src += sizeof(uint32_t);
   src += skip_padding(src);
 
@@ -79,27 +97,14 @@ read_irep_record_1(mrb_state *mrb, const uint8_t *bin, size_t *len, uint8_t flag
     if ((flags & FLAG_SRC_MALLOC) == 0 &&
         (flags & FLAG_BYTEORDER_NATIVE)) {
       irep->iseq = (mrb_code*)src;
-      src += sizeof(uint32_t) * irep->ilen;
+      src += sizeof(mrb_code) * irep->ilen;
       irep->flags |= MRB_ISEQ_NO_FREE;
     }
     else {
-      irep->iseq = (mrb_code *)mrb_malloc(mrb, sizeof(mrb_code) * irep->ilen);
-      if (flags & FLAG_BYTEORDER_NATIVE) {
-        memcpy(irep->iseq, src, sizeof(uint32_t) * irep->ilen);
-        src += sizeof(uint32_t) * irep->ilen;
-      }
-      else if (flags & FLAG_BYTEORDER_BIG) {
-        for (i = 0; i < irep->ilen; i++) {
-          irep->iseq[i] = (mrb_code)bin_to_uint32(src);     /* iseq */
-          src += sizeof(uint32_t);
-        }
-      }
-      else {
-        for (i = 0; i < irep->ilen; i++) {
-          irep->iseq[i] = (mrb_code)bin_to_uint32l(src);     /* iseq */
-          src += sizeof(uint32_t);
-        }
-      }
+      size_t data_len = sizeof(mrb_code) * irep->ilen;
+      irep->iseq = (mrb_code *)mrb_malloc(mrb, data_len);
+      memcpy(irep->iseq, src, data_len);
+      src += data_len;
     }
   }
 
@@ -138,7 +143,7 @@ read_irep_record_1(mrb_state *mrb, const uint8_t *bin, size_t *len, uint8_t flag
 
 #ifndef MRB_WITHOUT_FLOAT
       case IREP_TT_FLOAT:
-        irep->pool[i] = mrb_float_pool(mrb, mrb_str_to_dbl(mrb, s, FALSE));
+        irep->pool[i] = mrb_float_pool(mrb, str_to_double(mrb, s));
         break;
 #endif
 
@@ -157,7 +162,7 @@ read_irep_record_1(mrb_state *mrb, const uint8_t *bin, size_t *len, uint8_t flag
   }
 
   /* SYMS BLOCK */
-  irep->slen = (size_t)bin_to_uint32(src);  /* syms length */
+  irep->slen = (uint16_t)bin_to_uint32(src);  /* syms length */
   src += sizeof(uint32_t);
   if (irep->slen > 0) {
     if (SIZE_ERROR_MUL(irep->slen, sizeof(mrb_sym))) {
@@ -229,74 +234,6 @@ read_section_irep(mrb_state *mrb, const uint8_t *bin, uint8_t flags)
 }
 
 static int
-read_lineno_record_1(mrb_state *mrb, const uint8_t *bin, mrb_irep *irep, size_t *len)
-{
-  size_t i, fname_len, niseq;
-  char *fname;
-  uint16_t *lines;
-
-  *len = 0;
-  bin += sizeof(uint32_t); /* record size */
-  *len += sizeof(uint32_t);
-  fname_len = bin_to_uint16(bin);
-  bin += sizeof(uint16_t);
-  *len += sizeof(uint16_t);
-  fname = (char *)mrb_malloc(mrb, fname_len + 1);
-  memcpy(fname, bin, fname_len);
-  fname[fname_len] = '\0';
-  bin += fname_len;
-  *len += fname_len;
-
-  niseq = (size_t)bin_to_uint32(bin);
-  bin += sizeof(uint32_t); /* niseq */
-  *len += sizeof(uint32_t);
-
-  if (SIZE_ERROR_MUL(niseq, sizeof(uint16_t))) {
-    return MRB_DUMP_GENERAL_FAILURE;
-  }
-  lines = (uint16_t *)mrb_malloc(mrb, niseq * sizeof(uint16_t));
-  for (i = 0; i < niseq; i++) {
-    lines[i] = bin_to_uint16(bin);
-    bin += sizeof(uint16_t); /* niseq */
-    *len += sizeof(uint16_t);
-  }
-
-  irep->filename = fname;
-  irep->lines = lines;
-  return MRB_DUMP_OK;
-}
-
-static int
-read_lineno_record(mrb_state *mrb, const uint8_t *bin, mrb_irep *irep, size_t *lenp)
-{
-  int result = read_lineno_record_1(mrb, bin, irep, lenp);
-  int i;
-
-  if (result != MRB_DUMP_OK) return result;
-  for (i = 0; i < irep->rlen; i++) {
-    size_t len;
-
-    result = read_lineno_record(mrb, bin, irep->reps[i], &len);
-    if (result != MRB_DUMP_OK) break;
-    bin += len;
-    *lenp += len;
-  }
-  return result;
-}
-
-static int
-read_section_lineno(mrb_state *mrb, const uint8_t *bin, mrb_irep *irep)
-{
-  size_t len;
-
-  len = 0;
-  bin += sizeof(struct rite_section_lineno_header);
-
-  /* Read Binary Data Section */
-  return read_lineno_record(mrb, bin, irep, &len);
-}
-
-static int
 read_debug_record(mrb_state *mrb, const uint8_t *start, mrb_irep* irep, size_t *record_len, const mrb_sym *filenames, size_t filenames_len)
 {
   const uint8_t *bin = start;
@@ -320,7 +257,6 @@ read_debug_record(mrb_state *mrb, const uint8_t *start, mrb_irep* irep, size_t *
   for (f_idx = 0; f_idx < irep->debug_info->flen; ++f_idx) {
     mrb_irep_debug_info_file *file;
     uint16_t filename_idx;
-    mrb_int len;
 
     file = (mrb_irep_debug_info_file *)mrb_malloc(mrb, sizeof(*file));
     irep->debug_info->files[f_idx] = file;
@@ -333,8 +269,6 @@ read_debug_record(mrb_state *mrb, const uint8_t *start, mrb_irep* irep, size_t *
     bin += sizeof(uint16_t);
     mrb_assert(filename_idx < filenames_len);
     file->filename_sym = filenames[filename_idx];
-    len = 0;
-    file->filename = mrb_sym2name_len(mrb, file->filename_sym, &len);
 
     file->line_entry_count = bin_to_uint32(bin);
     bin += sizeof(uint32_t);
@@ -525,10 +459,14 @@ lv_exit:
 }
 
 static int
-read_binary_header(const uint8_t *bin, size_t *bin_size, uint16_t *crc, uint8_t *flags)
+read_binary_header(const uint8_t *bin, size_t bufsize, size_t *bin_size, uint16_t *crc, uint8_t *flags)
 {
   const struct rite_binary_header *header = (const struct rite_binary_header *)bin;
 
+  if (bufsize < sizeof(struct rite_binary_header)) {
+    return MRB_DUMP_READ_FAULT;
+  }
+
   if (memcmp(header->binary_ident, RITE_BINARY_IDENT, sizeof(header->binary_ident)) == 0) {
     if (bigendian_p())
       *flags |= FLAG_BYTEORDER_NATIVE;
@@ -545,16 +483,24 @@ read_binary_header(const uint8_t *bin, size_t *bin_size, uint16_t *crc, uint8_t
     return MRB_DUMP_INVALID_FILE_HEADER;
   }
 
+  if (memcmp(header->binary_version, RITE_BINARY_FORMAT_VER, sizeof(header->binary_version)) != 0) {
+    return MRB_DUMP_INVALID_FILE_HEADER;
+  }
+
   if (crc) {
     *crc = bin_to_uint16(header->binary_crc);
   }
   *bin_size = (size_t)bin_to_uint32(header->binary_size);
 
+  if (bufsize < *bin_size) {
+    return MRB_DUMP_READ_FAULT;
+  }
+
   return MRB_DUMP_OK;
 }
 
 static mrb_irep*
-read_irep(mrb_state *mrb, const uint8_t *bin, uint8_t flags)
+read_irep(mrb_state *mrb, const uint8_t *bin, size_t bufsize, uint8_t flags)
 {
   int result;
   mrb_irep *irep = NULL;
@@ -567,7 +513,7 @@ read_irep(mrb_state *mrb, const uint8_t *bin, uint8_t flags)
     return NULL;
   }
 
-  result = read_binary_header(bin, &bin_size, &crc, &flags);
+  result = read_binary_header(bin, bufsize, &bin_size, &crc, &flags);
   if (result != MRB_DUMP_OK) {
     return NULL;
   }
@@ -584,13 +530,6 @@ read_irep(mrb_state *mrb, const uint8_t *bin, uint8_t flags)
       irep = read_section_irep(mrb, bin, flags);
       if (!irep) return NULL;
     }
-    else if (memcmp(section_header->section_ident, RITE_SECTION_LINENO_IDENT, sizeof(section_header->section_ident)) == 0) {
-      if (!irep) return NULL;   /* corrupted data */
-      result = read_section_lineno(mrb, bin, irep);
-      if (result < MRB_DUMP_OK) {
-        return NULL;
-      }
-    }
     else if (memcmp(section_header->section_ident, RITE_SECTION_DEBUG_IDENT, sizeof(section_header->section_ident)) == 0) {
       if (!irep) return NULL;   /* corrupted data */
       result = read_section_debug(mrb, bin, irep, flags);
@@ -614,13 +553,19 @@ read_irep(mrb_state *mrb, const uint8_t *bin, uint8_t flags)
 mrb_irep*
 mrb_read_irep(mrb_state *mrb, const uint8_t *bin)
 {
-#ifdef MRB_USE_ETEXT_EDATA
+#if defined(MRB_USE_ETEXT_EDATA) || defined(MRB_USE_CUSTOM_RO_DATA_P)
   uint8_t flags = mrb_ro_data_p((char*)bin) ? FLAG_SRC_STATIC : FLAG_SRC_MALLOC;
 #else
   uint8_t flags = FLAG_SRC_STATIC;
 #endif
 
-  return read_irep(mrb, bin, flags);
+  return read_irep(mrb, bin, (size_t)-1, flags);
+}
+
+MRB_API mrb_irep*
+mrb_read_irep_buf(mrb_state *mrb, const void *buf, size_t bufsize)
+{
+  return read_irep(mrb, (const uint8_t *)buf, bufsize, FLAG_SRC_MALLOC);
 }
 
 void mrb_exc_set(mrb_state *mrb, mrb_value exc);
@@ -657,11 +602,23 @@ mrb_load_irep_cxt(mrb_state *mrb, const uint8_t *bin, mrbc_context *c)
 }
 
 MRB_API mrb_value
+mrb_load_irep_buf_cxt(mrb_state *mrb, const void *buf, size_t bufsize, mrbc_context *c)
+{
+  return load_irep(mrb, mrb_read_irep_buf(mrb, buf, bufsize), c);
+}
+
+MRB_API mrb_value
 mrb_load_irep(mrb_state *mrb, const uint8_t *bin)
 {
   return mrb_load_irep_cxt(mrb, bin, NULL);
 }
 
+MRB_API mrb_value
+mrb_load_irep_buf(mrb_state *mrb, const void *buf, size_t bufsize)
+{
+  return mrb_load_irep_buf_cxt(mrb, buf, bufsize, NULL);
+}
+
 #ifndef MRB_DISABLE_STDIO
 
 mrb_irep*
@@ -682,7 +639,7 @@ mrb_read_irep_file(mrb_state *mrb, FILE* fp)
   if (fread(buf, header_size, 1, fp) == 0) {
     goto irep_exit;
   }
-  result = read_binary_header(buf, &buf_size, NULL, &flags);
+  result = read_binary_header(buf, (size_t)-1, &buf_size, NULL, &flags);
   if (result != MRB_DUMP_OK || buf_size <= header_size) {
     goto irep_exit;
   }
@@ -691,7 +648,7 @@ mrb_read_irep_file(mrb_state *mrb, FILE* fp)
   if (fread(buf+header_size, buf_size-header_size, 1, fp) == 0) {
     goto irep_exit;
   }
-  irep = read_irep(mrb, buf, FLAG_SRC_MALLOC);
+  irep = read_irep(mrb, buf, (size_t)-1, FLAG_SRC_MALLOC);
 
 irep_exit:
   mrb_free(mrb, buf);
diff --git a/src/mruby_core.rake b/src/mruby_core.rake
index bb3d7b633..73fddb220 100644
--- a/src/mruby_core.rake
+++ b/src/mruby_core.rake
@@ -5,16 +5,15 @@ MRuby.each_target do
 
   objs = Dir.glob("#{current_dir}/*.c").map { |f|
     next nil if cxx_exception_enabled? and f =~ /(error|vm).c$/
-    next nil if self.cc.defines.flatten.include?("MRB_WITHOUT_FLOAT") and f =~ /fmt_fp.c$/
     objfile(f.pathmap("#{current_build_dir}/%n"))
   }.compact
 
   if cxx_exception_enabled?
     objs += %w(vm error).map { |v| compile_as_cxx "#{current_dir}/#{v}.c", "#{current_build_dir}/#{v}.cxx" }
   end
-  self.libmruby << objs
+  self.libmruby_objs << objs
 
-  file libfile("#{build_dir}/lib/libmruby_core") => objs do |t|
+  file libmruby_core_static => objs do |t|
     archiver.run t.name, t.prerequisites
   end
 end
diff --git a/src/numeric.c b/src/numeric.c
index 4e5fc394e..4288df44a 100644
--- a/src/numeric.c
+++ b/src/numeric.c
@@ -10,6 +10,7 @@
 #endif
 #include <limits.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include <mruby.h>
 #include <mruby/array.h>
@@ -23,9 +24,9 @@
 #define floor(f) floorf(f)
 #define ceil(f) ceilf(f)
 #define fmod(x,y) fmodf(x,y)
-#define MRB_FLO_TO_STR_FMT "%.8g"
+#define FLO_TO_STR_PREC 8
 #else
-#define MRB_FLO_TO_STR_FMT "%.16g"
+#define FLO_TO_STR_PREC 16
 #endif
 #endif
 
@@ -43,6 +44,15 @@ mrb_to_flo(mrb_state *mrb, mrb_value val)
   }
   return mrb_float(val);
 }
+
+MRB_API mrb_value
+mrb_int_value(mrb_state *mrb, mrb_float f)
+{
+  if (FIXABLE_FLOAT(f)) {
+    return mrb_fixnum_value((mrb_int)f);
+  }
+  return mrb_float_value(mrb, f);
+}
 #endif
 
 /*
@@ -55,7 +65,7 @@ mrb_to_flo(mrb_state *mrb, mrb_value val)
  *    2.0**3      #=> 8.0
  */
 static mrb_value
-num_pow(mrb_state *mrb, mrb_value x)
+integral_pow(mrb_state *mrb, mrb_value x)
 {
   mrb_value y;
 #ifndef MRB_WITHOUT_FLOAT
@@ -102,6 +112,25 @@ num_pow(mrb_state *mrb, mrb_value x)
 #endif
 }
 
+static mrb_value
+integral_idiv(mrb_state *mrb, mrb_value x)
+{
+#ifdef MRB_WITHOUT_FLOAT
+  mrb_value y;
+
+  mrb_get_args(mrb, "o", &y);
+  if (!mrb_fixnum_p(y)) {
+    mrb_raise(mrb, E_TYPE_ERROR, "non fixnum value");
+  }
+  return mrb_fixnum_value(mrb_fixnum(x) / mrb_fixnum(y));
+#else
+  mrb_float y;
+
+  mrb_get_args(mrb, "f", &y);
+  return mrb_int_value(mrb, mrb_to_flo(mrb, x) / y);
+#endif
+}
+
 /* 15.2.8.3.4  */
 /* 15.2.9.3.4  */
 /*
@@ -113,19 +142,6 @@ num_pow(mrb_state *mrb, mrb_value x)
  * result.
  */
 
-mrb_value
-mrb_num_div(mrb_state *mrb, mrb_value x, mrb_value y)
-{
-#ifdef MRB_WITHOUT_FLOAT
-  if (!mrb_fixnum_p(y)) {
-    mrb_raise(mrb, E_TYPE_ERROR, "non fixnum value");
-  }
-  return mrb_fixnum_value(mrb_fixnum(x) / mrb_fixnum(y));
-#else
-  return mrb_float_value(mrb, mrb_to_flo(mrb, x) / mrb_to_flo(mrb, y));
-#endif
-}
-
 /* 15.2.9.3.19(x) */
 /*
  *  call-seq:
@@ -135,7 +151,7 @@ mrb_num_div(mrb_state *mrb, mrb_value x, mrb_value y)
  */
 
 static mrb_value
-num_div(mrb_state *mrb, mrb_value x)
+integral_div(mrb_state *mrb, mrb_value x)
 {
 #ifdef MRB_WITHOUT_FLOAT
   mrb_value y;
@@ -153,6 +169,22 @@ num_div(mrb_state *mrb, mrb_value x)
 #endif
 }
 
+static mrb_value
+integral_coerce_step_counter(mrb_state *mrb, mrb_value self)
+{
+  mrb_value num, step;
+
+  mrb_get_args(mrb, "oo", &num, &step);
+
+#ifndef MRB_WITHOUT_FLOAT
+  if (mrb_float_p(self) || mrb_float_p(num) || mrb_float_p(step)) {
+    return mrb_Float(mrb, self);
+  }
+#endif
+
+  return self;
+}
+
 #ifndef MRB_WITHOUT_FLOAT
 /********************************************************************
  *
@@ -177,10 +209,49 @@ num_div(mrb_state *mrb, mrb_value x)
 static mrb_value
 flo_to_s(mrb_state *mrb, mrb_value flt)
 {
-  if (isnan(mrb_float(flt))) {
+  mrb_float f = mrb_float(flt);
+
+  if (isinf(f)) {
+    return f < 0 ? mrb_str_new_lit(mrb, "-Infinity")
+                 : mrb_str_new_lit(mrb, "Infinity");
+  }
+  else if (isnan(f)) {
     return mrb_str_new_lit(mrb, "NaN");
   }
-  return mrb_float_to_str(mrb, flt, MRB_FLO_TO_STR_FMT);
+  else {
+    char fmt[] = "%." MRB_STRINGIZE(FLO_TO_STR_PREC) "g";
+    mrb_value str = mrb_float_to_str(mrb, flt, fmt);
+    mrb_int len;
+    char *begp, *p, *endp;
+
+    insert_dot_zero:
+    begp = RSTRING_PTR(str);
+    len = RSTRING_LEN(str);
+    for (p = begp, endp = p + len; p < endp; ++p) {
+      if (*p == '.') {
+        return str;
+      }
+      else if (*p == 'e') {
+        ptrdiff_t e_pos = p - begp;
+        mrb_str_cat(mrb, str, ".0", 2);
+        p = RSTRING_PTR(str) + e_pos;
+        memmove(p + 2, p, len - e_pos);
+        memcpy(p, ".0", 2);
+        return str;
+      }
+    }
+
+    if (FLO_TO_STR_PREC + (begp[0] == '-') <= len) {
+      --fmt[sizeof(fmt) - 3];  /* %.16g(%.8g) -> %.15g(%.7g) */
+      str = mrb_float_to_str(mrb, flt, fmt);
+      goto insert_dot_zero;
+    }
+    else {
+      mrb_str_cat(mrb, str, ".0", 2);
+    }
+
+    return str;
+  }
 }
 
 /* 15.2.9.3.2  */
@@ -220,29 +291,40 @@ flo_mul(mrb_state *mrb, mrb_value x)
 }
 
 static void
-flodivmod(mrb_state *mrb, mrb_float x, mrb_float y, mrb_float *divp, mrb_float *modp)
+flodivmod(mrb_state *mrb, double x, double y, mrb_float *divp, mrb_float *modp)
 {
-  mrb_float div;
-  mrb_float mod;
+  double div, mod;
 
+  if (isnan(y)) {
+    /* y is NaN so all results are NaN */
+    div = mod = y;
+    goto exit;
+  }
   if (y == 0.0) {
-    if (x > 0.0) div = INFINITY;
-    else if (x < 0.0) div = -INFINITY;
-    else div = NAN;             /* x == 0.0 */
+    if (x == 0) div = NAN;
+    else if (x > 0.0) div = INFINITY;
+    else div = -INFINITY;       /* x < 0.0 */
     mod = NAN;
+    goto exit;
+  }
+  if ((x == 0.0) || (isinf(y) && !isinf(x))) {
+    mod = x;
   }
   else {
     mod = fmod(x, y);
-    if (isinf(x) && isfinite(y))
-      div = x;
-    else
-      div = (x - mod) / y;
-    if (y*mod < 0) {
-      mod += y;
-      div -= 1.0;
-    }
   }
-
+  if (isinf(x) && !isinf(y)) {
+    div = x;
+  }
+  else {
+    div = (x - mod) / y;
+    if (modp && divp) div = round(div);
+  }
+  if (y*mod < 0) {
+    mod += y;
+    div -= 1.0;
+  }
+ exit:
   if (modp) *modp = mod;
   if (divp) *divp = div;
 }
@@ -302,7 +384,7 @@ flo_eql(mrb_state *mrb, mrb_value x)
 
   mrb_get_args(mrb, "o", &y);
   if (!mrb_float_p(y)) return mrb_false_value();
-  return mrb_bool_value(mrb_float(x) == (mrb_float)mrb_fixnum(y));
+  return mrb_bool_value(mrb_float(x) == mrb_float(y));
 }
 
 /* 15.2.9.3.7  */
@@ -354,7 +436,7 @@ value_int64(mrb_state *mrb, mrb_value x)
 static mrb_value
 int64_value(mrb_state *mrb, int64_t v)
 {
-  if (FIXABLE(v)) {
+  if (TYPED_FIXABLE(v,int64_t)) {
     return mrb_fixnum_value((mrb_int)v);
   }
   return mrb_float_value(mrb, (mrb_float)v);
@@ -417,12 +499,16 @@ flo_shift(mrb_state *mrb, mrb_value x, mrb_int width)
   if (width < 0) {
     while (width++) {
       val /= 2;
+      if (val < 1.0) {
+        val = 0;
+        break;
+      }
     }
 #if defined(_ISOC99_SOURCE)
     val = trunc(val);
 #else
     if (val > 0){
-        val = floor(val);    
+        val = floor(val);
     } else {
         val = ceil(val);
     }
@@ -436,14 +522,11 @@ flo_shift(mrb_state *mrb, mrb_value x, mrb_int width)
       val *= 2;
     }
   }
-  if (FIXABLE_FLOAT(val)) {
-    return mrb_fixnum_value((mrb_int)val);
-  }
-  return mrb_float_value(mrb, val);
+  return mrb_int_value(mrb, val);
 }
 
 static mrb_value
-flo_lshift(mrb_state *mrb, mrb_value x)
+flo_rshift(mrb_state *mrb, mrb_value x)
 {
   mrb_int width;
 
@@ -452,7 +535,7 @@ flo_lshift(mrb_state *mrb, mrb_value x)
 }
 
 static mrb_value
-flo_rshift(mrb_state *mrb, mrb_value x)
+flo_lshift(mrb_state *mrb, mrb_value x)
 {
   mrb_int width;
 
@@ -545,10 +628,7 @@ flo_floor(mrb_state *mrb, mrb_value num)
   mrb_float f = floor(mrb_float(num));
 
   mrb_check_num_exact(mrb, f);
-  if (!FIXABLE_FLOAT(f)) {
-    return mrb_float_value(mrb, f);
-  }
-  return mrb_fixnum_value((mrb_int)f);
+  return mrb_int_value(mrb, f);
 }
 
 /* 15.2.9.3.8  */
@@ -571,10 +651,7 @@ flo_ceil(mrb_state *mrb, mrb_value num)
   mrb_float f = ceil(mrb_float(num));
 
   mrb_check_num_exact(mrb, f);
-  if (!FIXABLE_FLOAT(f)) {
-    return mrb_float_value(mrb, f);
-  }
-  return mrb_fixnum_value((mrb_int)f);
+  return mrb_int_value(mrb, f);
 }
 
 /* 15.2.9.3.12 */
@@ -655,7 +732,7 @@ flo_round(mrb_state *mrb, mrb_value num)
     if (!isfinite(number)) return num;
     return mrb_float_value(mrb, number);
   }
-  return mrb_fixnum_value((mrb_int)number);
+  return mrb_int_value(mrb, number);
 }
 
 /* 15.2.9.3.14 */
@@ -663,7 +740,6 @@ flo_round(mrb_state *mrb, mrb_value num)
 /*
  *  call-seq:
  *     flt.to_i      ->  integer
- *     flt.to_int    ->  integer
  *     flt.truncate  ->  integer
  *
  *  Returns <i>flt</i> truncated to an <code>Integer</code>.
@@ -678,10 +754,7 @@ flo_truncate(mrb_state *mrb, mrb_value num)
   if (f < 0.0) f = ceil(f);
 
   mrb_check_num_exact(mrb, f);
-  if (!FIXABLE_FLOAT(f)) {
-    return mrb_float_value(mrb, f);
-  }
-  return mrb_fixnum_value((mrb_int)f);
+  return mrb_int_value(mrb, f);
 }
 
 static mrb_value
@@ -703,7 +776,6 @@ flo_nan_p(mrb_state *mrb, mrb_value num)
 /*
  *  call-seq:
  *     int.to_i      ->  integer
- *     int.to_int    ->  integer
  *
  *  As <i>int</i> is already an <code>Integer</code>, all these
  *  methods simply return the receiver.
@@ -715,8 +787,8 @@ int_to_i(mrb_state *mrb, mrb_value num)
   return num;
 }
 
-mrb_value
-mrb_fixnum_mul(mrb_state *mrb, mrb_value x, mrb_value y)
+static mrb_value
+fixnum_mul(mrb_state *mrb, mrb_value x, mrb_value y)
 {
   mrb_int a;
 
@@ -740,6 +812,21 @@ mrb_fixnum_mul(mrb_state *mrb, mrb_value x, mrb_value y)
 #endif
 }
 
+MRB_API mrb_value
+mrb_num_mul(mrb_state *mrb, mrb_value x, mrb_value y)
+{
+  if (mrb_fixnum_p(x)) {
+    return fixnum_mul(mrb, x, y);
+  }
+#ifndef MRB_WITHOUT_FLOAT
+  if (mrb_float_p(x)) {
+    return mrb_float_value(mrb, mrb_float(x) * mrb_to_flo(mrb, y));
+  }
+#endif
+  mrb_raise(mrb, E_TYPE_ERROR, "no number multiply");
+  return mrb_nil_value();       /* not reached */
+}
+
 /* 15.2.8.3.3  */
 /*
  * call-seq:
@@ -756,7 +843,7 @@ fix_mul(mrb_state *mrb, mrb_value x)
   mrb_value y;
 
   mrb_get_args(mrb, "o", &y);
-  return mrb_fixnum_mul(mrb, x, y);
+  return fixnum_mul(mrb, x, y);
 }
 
 static void
@@ -868,7 +955,7 @@ fix_divmod(mrb_state *mrb, mrb_value x)
     mrb_value a, b;
 
     flodivmod(mrb, (mrb_float)mrb_fixnum(x), mrb_to_flo(mrb, y), &div, &mod);
-    a = mrb_float_value(mrb, div);
+    a = mrb_int_value(mrb, div);
     b = mrb_float_value(mrb, mod);
     return mrb_assoc_new(mrb, a, b);
   }
@@ -886,7 +973,7 @@ flo_divmod(mrb_state *mrb, mrb_value x)
   mrb_get_args(mrb, "o", &y);
 
   flodivmod(mrb, mrb_float(x), mrb_to_flo(mrb, y), &div, &mod);
-  a = mrb_float_value(mrb, div);
+  a = mrb_int_value(mrb, div);
   b = mrb_float_value(mrb, mod);
   return mrb_assoc_new(mrb, a, b);
 }
@@ -1141,7 +1228,7 @@ fix_to_f(mrb_state *mrb, mrb_value num)
  *  (in particular infinite or NaN)
  *  to numerical classes which don't support them.
  *
- *     Float::INFINITY.to_r
+ *     Float::INFINITY.to_i
  *
  *  <em>raises the exception:</em>
  *
@@ -1160,25 +1247,20 @@ mrb_flo_to_fixnum(mrb_state *mrb, mrb_value x)
   else {
     mrb_float d = mrb_float(x);
 
-    if (isinf(d)) {
-      mrb_raise(mrb, E_FLOATDOMAIN_ERROR, d < 0 ? "-Infinity" : "Infinity");
-    }
-    if (isnan(d)) {
-      mrb_raise(mrb, E_FLOATDOMAIN_ERROR, "NaN");
-    }
+    mrb_check_num_exact(mrb, d);
     if (FIXABLE_FLOAT(d)) {
       z = (mrb_int)d;
     }
     else {
-      mrb_raisef(mrb, E_ARGUMENT_ERROR, "number (%S) too big for integer", x);
+      mrb_raisef(mrb, E_RANGE_ERROR, "number (%S) too big for integer", x);
     }
   }
   return mrb_fixnum_value(z);
 }
 #endif
 
-mrb_value
-mrb_fixnum_plus(mrb_state *mrb, mrb_value x, mrb_value y)
+static mrb_value
+fixnum_plus(mrb_state *mrb, mrb_value x, mrb_value y)
 {
   mrb_int a;
 
@@ -1202,6 +1284,21 @@ mrb_fixnum_plus(mrb_state *mrb, mrb_value x, mrb_value y)
 #endif
 }
 
+MRB_API mrb_value
+mrb_num_plus(mrb_state *mrb, mrb_value x, mrb_value y)
+{
+  if (mrb_fixnum_p(x)) {
+    return fixnum_plus(mrb, x, y);
+  }
+#ifndef MRB_WITHOUT_FLOAT
+  if (mrb_float_p(x)) {
+    return mrb_float_value(mrb, mrb_float(x) + mrb_to_flo(mrb, y));
+  }
+#endif
+  mrb_raise(mrb, E_TYPE_ERROR, "no number addition");
+  return mrb_nil_value();       /* not reached */
+}
+
 /* 15.2.8.3.1  */
 /*
  * call-seq:
@@ -1217,11 +1314,11 @@ fix_plus(mrb_state *mrb, mrb_value self)
   mrb_value other;
 
   mrb_get_args(mrb, "o", &other);
-  return mrb_fixnum_plus(mrb, self, other);
+  return fixnum_plus(mrb, self, other);
 }
 
-mrb_value
-mrb_fixnum_minus(mrb_state *mrb, mrb_value x, mrb_value y)
+static mrb_value
+fixnum_minus(mrb_state *mrb, mrb_value x, mrb_value y)
 {
   mrb_int a;
 
@@ -1244,6 +1341,21 @@ mrb_fixnum_minus(mrb_state *mrb, mrb_value x, mrb_value y)
 #endif
 }
 
+MRB_API mrb_value
+mrb_num_minus(mrb_state *mrb, mrb_value x, mrb_value y)
+{
+  if (mrb_fixnum_p(x)) {
+    return fixnum_minus(mrb, x, y);
+  }
+#ifndef MRB_WITHOUT_FLOAT
+  if (mrb_float_p(x)) {
+    return mrb_float_value(mrb, mrb_float(x) - mrb_to_flo(mrb, y));
+  }
+#endif
+  mrb_raise(mrb, E_TYPE_ERROR, "no number subtraction");
+  return mrb_nil_value();       /* not reached */
+}
+
 /* 15.2.8.3.2  */
 /* 15.2.8.3.16 */
 /*
@@ -1260,7 +1372,7 @@ fix_minus(mrb_state *mrb, mrb_value self)
   mrb_value other;
 
   mrb_get_args(mrb, "o", &other);
-  return mrb_fixnum_minus(mrb, self, other);
+  return fixnum_minus(mrb, self, other);
 }
 
 
@@ -1370,7 +1482,7 @@ cmpnum(mrb_state *mrb, mrb_value v1, mrb_value v2)
  *  basis for the tests in <code>Comparable</code>.
  */
 static mrb_value
-num_cmp(mrb_state *mrb, mrb_value self)
+integral_cmp(mrb_state *mrb, mrb_value self)
 {
   mrb_value other;
   mrb_int n;
@@ -1390,7 +1502,7 @@ cmperr(mrb_state *mrb, mrb_value v1, mrb_value v2)
 }
 
 static mrb_value
-num_lt(mrb_state *mrb, mrb_value self)
+integral_lt(mrb_state *mrb, mrb_value self)
 {
   mrb_value other;
   mrb_int n;
@@ -1403,7 +1515,7 @@ num_lt(mrb_state *mrb, mrb_value self)
 }
 
 static mrb_value
-num_le(mrb_state *mrb, mrb_value self)
+integral_le(mrb_state *mrb, mrb_value self)
 {
   mrb_value other;
   mrb_int n;
@@ -1416,7 +1528,7 @@ num_le(mrb_state *mrb, mrb_value self)
 }
 
 static mrb_value
-num_gt(mrb_state *mrb, mrb_value self)
+integral_gt(mrb_state *mrb, mrb_value self)
 {
   mrb_value other;
   mrb_int n;
@@ -1429,7 +1541,7 @@ num_gt(mrb_state *mrb, mrb_value self)
 }
 
 static mrb_value
-num_ge(mrb_state *mrb, mrb_value self)
+integral_ge(mrb_state *mrb, mrb_value self)
 {
   mrb_value other;
   mrb_int n;
@@ -1478,22 +1590,25 @@ flo_plus(mrb_state *mrb, mrb_value x)
 void
 mrb_init_numeric(mrb_state *mrb)
 {
-  struct RClass *numeric, *integer, *fixnum;
+  struct RClass *numeric, *integer, *fixnum, *integral;
 #ifndef MRB_WITHOUT_FLOAT
   struct RClass *fl;
 #endif
 
+  integral = mrb_define_module(mrb, "Integral");
+  mrb_define_method(mrb, integral,"**",       integral_pow,    MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, integral,"/",        integral_div,    MRB_ARGS_REQ(1)); /* 15.2.{8,9}.3.6  */
+  mrb_define_method(mrb, integral,"quo",      integral_div,    MRB_ARGS_REQ(1)); /* 15.2.7.4.5 (x) */
+  mrb_define_method(mrb, integral,"div",      integral_idiv,   MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, integral,"<=>",      integral_cmp,    MRB_ARGS_REQ(1)); /* 15.2.{8,9}.3.1  */
+  mrb_define_method(mrb, integral,"<",        integral_lt,     MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, integral,"<=",       integral_le,     MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, integral,">",        integral_gt,     MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, integral,">=",       integral_ge,     MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, integral,"__coerce_step_counter", integral_coerce_step_counter, MRB_ARGS_REQ(2));
+
   /* Numeric Class */
   numeric = mrb_define_class(mrb, "Numeric",  mrb->object_class);                /* 15.2.7 */
-
-  mrb_define_method(mrb, numeric, "**",       num_pow,         MRB_ARGS_REQ(1));
-  mrb_define_method(mrb, numeric, "/",        num_div,         MRB_ARGS_REQ(1)); /* 15.2.8.3.4  */
-  mrb_define_method(mrb, numeric, "quo",      num_div,         MRB_ARGS_REQ(1)); /* 15.2.7.4.5 (x) */
-  mrb_define_method(mrb, numeric, "<=>",      num_cmp,         MRB_ARGS_REQ(1)); /* 15.2.9.3.6  */
-  mrb_define_method(mrb, numeric, "<",        num_lt,          MRB_ARGS_REQ(1));
-  mrb_define_method(mrb, numeric, "<=",       num_le,          MRB_ARGS_REQ(1));
-  mrb_define_method(mrb, numeric, ">",        num_gt,          MRB_ARGS_REQ(1));
-  mrb_define_method(mrb, numeric, ">=",       num_ge,          MRB_ARGS_REQ(1));
   mrb_define_method(mrb, numeric, "finite?",  num_finite_p,    MRB_ARGS_NONE());
   mrb_define_method(mrb, numeric, "infinite?",num_infinite_p,  MRB_ARGS_NONE());
 
@@ -1545,8 +1660,8 @@ mrb_init_numeric(mrb_state *mrb)
   mrb_define_method(mrb, fl,      "&",         flo_and,        MRB_ARGS_REQ(1));
   mrb_define_method(mrb, fl,      "|",         flo_or,         MRB_ARGS_REQ(1));
   mrb_define_method(mrb, fl,      "^",         flo_xor,        MRB_ARGS_REQ(1));
-  mrb_define_method(mrb, fl,      ">>",        flo_lshift,     MRB_ARGS_REQ(1));
-  mrb_define_method(mrb, fl,      "<<",        flo_rshift,     MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, fl,      ">>",        flo_rshift,     MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, fl,      "<<",        flo_lshift,     MRB_ARGS_REQ(1));
   mrb_define_method(mrb, fl,      "ceil",      flo_ceil,       MRB_ARGS_NONE()); /* 15.2.9.3.8  */
   mrb_define_method(mrb, fl,      "finite?",   flo_finite_p,   MRB_ARGS_NONE()); /* 15.2.9.3.9  */
   mrb_define_method(mrb, fl,      "floor",     flo_floor,      MRB_ARGS_NONE()); /* 15.2.9.3.10 */
@@ -1569,6 +1684,7 @@ mrb_init_numeric(mrb_state *mrb)
 #ifdef NAN
   mrb_define_const(mrb, fl, "NAN", mrb_float_value(mrb, NAN));
 #endif
+
+  mrb_include_module(mrb, fl, integral);
 #endif
-  mrb_define_module(mrb, "Integral");
 }
diff --git a/src/object.c b/src/object.c
index 8724c5416..7c1879019 100644
--- a/src/object.c
+++ b/src/object.c
@@ -323,19 +323,6 @@ convert_type(mrb_state *mrb, mrb_value val, const char *tname, const char *metho
 }
 
 MRB_API mrb_value
-mrb_check_to_integer(mrb_state *mrb, mrb_value val, const char *method)
-{
-  mrb_value v;
-
-  if (mrb_fixnum_p(val)) return val;
-  v = convert_type(mrb, val, "Integer", method, FALSE);
-  if (mrb_nil_p(v) || !mrb_fixnum_p(v)) {
-    return mrb_nil_value();
-  }
-  return v;
-}
-
-MRB_API mrb_value
 mrb_convert_type(mrb_state *mrb, mrb_value val, enum mrb_vtype type, const char *tname, const char *method)
 {
   mrb_value v;
@@ -447,8 +434,10 @@ mrb_any_to_s(mrb_state *mrb, mrb_value obj)
 
   mrb_str_cat_lit(mrb, str, "#<");
   mrb_str_cat_cstr(mrb, str, cname);
-  mrb_str_cat_lit(mrb, str, ":");
-  mrb_str_concat(mrb, str, mrb_ptr_to_str(mrb, mrb_ptr(obj)));
+  if (!mrb_immediate_p(obj)) {
+    mrb_str_cat_lit(mrb, str, ":");
+    mrb_str_concat(mrb, str, mrb_ptr_to_str(mrb, mrb_ptr(obj)));
+  }
   mrb_str_cat_lit(mrb, str, ">");
 
   return str;
@@ -505,25 +494,22 @@ mrb_obj_is_kind_of(mrb_state *mrb, mrb_value obj, struct RClass *c)
   return FALSE;
 }
 
-static mrb_value
-mrb_to_integer(mrb_state *mrb, mrb_value val, const char *method)
-{
-  mrb_value v;
-
-  if (mrb_fixnum_p(val)) return val;
-  v = convert_type(mrb, val, "Integer", method, TRUE);
-  if (!mrb_obj_is_kind_of(mrb, v, mrb->fixnum_class)) {
-    mrb_value type = inspect_type(mrb, val);
-    mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S to Integer (%S#%S gives %S)",
-               type, type, mrb_str_new_cstr(mrb, method), inspect_type(mrb, v));
-  }
-  return v;
-}
-
 MRB_API mrb_value
 mrb_to_int(mrb_state *mrb, mrb_value val)
 {
-  return mrb_to_integer(mrb, val, "to_int");
+
+  if (!mrb_fixnum_p(val)) {
+    mrb_value type;
+
+#ifndef MRB_WITHOUT_FLOAT
+    if (mrb_float_p(val)) {
+      return mrb_flo_to_fixnum(mrb, val);
+    }
+#endif
+    type = inspect_type(mrb, val);
+    mrb_raisef(mrb, E_TYPE_ERROR, "can't convert %S to Integer", type);
+  }
+  return val;
 }
 
 MRB_API mrb_value
@@ -533,18 +519,12 @@ mrb_convert_to_integer(mrb_state *mrb, mrb_value val, mrb_int base)
 
   if (mrb_nil_p(val)) {
     if (base != 0) goto arg_error;
-      mrb_raise(mrb, E_TYPE_ERROR, "can't convert nil into Integer");
+    mrb_raise(mrb, E_TYPE_ERROR, "can't convert nil into Integer");
   }
   switch (mrb_type(val)) {
 #ifndef MRB_WITHOUT_FLOAT
     case MRB_TT_FLOAT:
       if (base != 0) goto arg_error;
-      else {
-        mrb_float f = mrb_float(val);
-        if (FIXABLE_FLOAT(f)) {
-          break;
-        }
-      }
       return mrb_flo_to_fixnum(mrb, val);
 #endif
 
@@ -568,11 +548,8 @@ mrb_convert_to_integer(mrb_state *mrb, mrb_value val, mrb_int base)
 arg_error:
     mrb_raise(mrb, E_ARGUMENT_ERROR, "base specified for non string value");
   }
-  tmp = convert_type(mrb, val, "Integer", "to_int", FALSE);
-  if (mrb_nil_p(tmp) || !mrb_fixnum_p(tmp)) {
-    tmp = mrb_to_integer(mrb, val, "to_i");
-  }
-  return tmp;
+  /* to raise TypeError */
+  return mrb_to_int(mrb, val);
 }
 
 MRB_API mrb_value
@@ -605,6 +582,70 @@ mrb_Float(mrb_state *mrb, mrb_value val)
 #endif
 
 MRB_API mrb_value
+mrb_to_str(mrb_state *mrb, mrb_value val)
+{
+  return mrb_ensure_string_type(mrb, val);
+}
+
+/* obsolete: use mrb_ensure_string_type() instead */
+MRB_API mrb_value
+mrb_string_type(mrb_state *mrb, mrb_value str)
+{
+  return mrb_ensure_string_type(mrb, str);
+}
+
+MRB_API mrb_value
+mrb_ensure_string_type(mrb_state *mrb, mrb_value str)
+{
+  if (!mrb_string_p(str)) {
+    mrb_raisef(mrb, E_TYPE_ERROR, "%S cannot be converted to String",
+               inspect_type(mrb, str));
+  }
+  return str;
+}
+
+MRB_API mrb_value
+mrb_check_string_type(mrb_state *mrb, mrb_value str)
+{
+  if (!mrb_string_p(str)) return mrb_nil_value();
+  return str;
+}
+
+MRB_API mrb_value
+mrb_ensure_array_type(mrb_state *mrb, mrb_value ary)
+{
+  if (!mrb_array_p(ary)) {
+    mrb_raisef(mrb, E_TYPE_ERROR, "%S cannot be converted to Array",
+               inspect_type(mrb, ary));
+  }
+  return ary;
+}
+
+MRB_API mrb_value
+mrb_check_array_type(mrb_state *mrb, mrb_value ary)
+{
+  if (!mrb_array_p(ary)) return mrb_nil_value();
+  return ary;
+}
+
+MRB_API mrb_value
+mrb_ensure_hash_type(mrb_state *mrb, mrb_value hash)
+{
+  if (!mrb_hash_p(hash)) {
+    mrb_raisef(mrb, E_TYPE_ERROR, "%S cannot be converted to Hash",
+               inspect_type(mrb, hash));
+  }
+  return hash;
+}
+
+MRB_API mrb_value
+mrb_check_hash_type(mrb_state *mrb, mrb_value hash)
+{
+  if (!mrb_hash_p(hash)) return mrb_nil_value();
+  return hash;
+}
+
+MRB_API mrb_value
 mrb_inspect(mrb_state *mrb, mrb_value obj)
 {
   return mrb_obj_as_string(mrb, mrb_funcall(mrb, obj, "inspect", 0));
diff --git a/src/proc.c b/src/proc.c
index c6e9be433..094fff816 100644
--- a/src/proc.c
+++ b/src/proc.c
@@ -10,7 +10,7 @@
 #include <mruby/opcode.h>
 
 static mrb_code call_iseq[] = {
-  MKOP_A(OP_CALL, 0),
+  OP_CALL,
 };
 
 struct RProc*
@@ -63,12 +63,12 @@ closure_setup(mrb_state *mrb, struct RProc *p)
 {
   mrb_callinfo *ci = mrb->c->ci;
   struct RProc *up = p->upper;
-  struct REnv *e;
+  struct REnv *e = NULL;
 
-  if (ci->env) {
+  if (ci && ci->env) {
     e = ci->env;
   }
-  else {
+  else if (up) {
     struct RClass *tc = MRB_PROC_TARGET_CLASS(p);
 
     e = env_new(mrb, up->body.irep->nlocals);
@@ -78,9 +78,11 @@ closure_setup(mrb_state *mrb, struct RProc *p)
       mrb_field_write_barrier(mrb, (struct RBasic*)e, (struct RBasic*)tc);
     }
   }
-  p->e.env = e;
-  p->flags |= MRB_PROC_ENVSET;
-  mrb_field_write_barrier(mrb, (struct RBasic*)p, (struct RBasic*)e);
+  if (e) {
+    p->e.env = e;
+    p->flags |= MRB_PROC_ENVSET;
+    mrb_field_write_barrier(mrb, (struct RBasic*)p, (struct RBasic*)e);
+  }
 }
 
 struct RProc*
@@ -211,46 +213,11 @@ mrb_proc_init_copy(mrb_state *mrb, mrb_value self)
   return self;
 }
 
-int
-mrb_proc_cfunc_p(struct RProc *p)
-{
-  return MRB_PROC_CFUNC_P(p);
-}
-
 /* 15.2.17.4.2 */
 static mrb_value
-mrb_proc_arity(mrb_state *mrb, mrb_value self)
+proc_arity(mrb_state *mrb, mrb_value self)
 {
-  struct RProc *p = mrb_proc_ptr(self);
-  struct mrb_irep *irep;
-  mrb_code *iseq;
-  mrb_aspec aspec;
-  int ma, op, ra, pa, arity;
-
-  if (MRB_PROC_CFUNC_P(p)) {
-    /* TODO cfunc aspec not implemented yet */
-    return mrb_fixnum_value(-1);
-  }
-
-  irep = p->body.irep;
-  if (!irep) {
-    return mrb_fixnum_value(0);
-  }
-
-  iseq = irep->iseq;
-  /* arity is depend on OP_ENTER */
-  if (GET_OPCODE(*iseq) != OP_ENTER) {
-    return mrb_fixnum_value(0);
-  }
-
-  aspec = GETARG_Ax(*iseq);
-  ma = MRB_ASPEC_REQ(aspec);
-  op = MRB_ASPEC_OPT(aspec);
-  ra = MRB_ASPEC_REST(aspec);
-  pa = MRB_ASPEC_POST(aspec);
-  arity = ra || (MRB_PROC_STRICT_P(p) && op) ? -(ma + pa + 1) : ma + pa;
-
-  return mrb_fixnum_value(arity);
+  return mrb_fixnum_value(mrb_proc_arity(mrb_proc_ptr(self)));
 }
 
 /* 15.3.1.2.6  */
@@ -285,6 +252,40 @@ proc_lambda(mrb_state *mrb, mrb_value self)
   return blk;
 }
 
+mrb_int
+mrb_proc_arity(const struct RProc *p)
+{
+  struct mrb_irep *irep;
+  mrb_code *pc;
+  mrb_aspec aspec;
+  int ma, op, ra, pa, arity;
+
+  if (MRB_PROC_CFUNC_P(p)) {
+    /* TODO cfunc aspec not implemented yet */
+    return -1;
+  }
+
+  irep = p->body.irep;
+  if (!irep) {
+    return 0;
+  }
+
+  pc = irep->iseq;
+  /* arity is depend on OP_ENTER */
+  if (*pc != OP_ENTER) {
+    return 0;
+  }
+
+  aspec = PEEK_W(pc+1);
+  ma = MRB_ASPEC_REQ(aspec);
+  op = MRB_ASPEC_OPT(aspec);
+  ra = MRB_ASPEC_REST(aspec);
+  pa = MRB_ASPEC_POST(aspec);
+  arity = ra || (MRB_PROC_STRICT_P(p) && op) ? -(ma + pa + 1) : ma + pa;
+
+  return arity;
+}
+
 void
 mrb_init_proc(mrb_state *mrb)
 {
@@ -299,15 +300,15 @@ mrb_init_proc(mrb_state *mrb)
   call_irep->ilen = 1;
   call_irep->nregs = 2;         /* receiver and block */
 
-  mrb_define_class_method(mrb, mrb->proc_class, "new", mrb_proc_s_new, MRB_ARGS_ANY());
+  mrb_define_class_method(mrb, mrb->proc_class, "new", mrb_proc_s_new, MRB_ARGS_NONE()|MRB_ARGS_BLOCK());
   mrb_define_method(mrb, mrb->proc_class, "initialize_copy", mrb_proc_init_copy, MRB_ARGS_REQ(1));
-  mrb_define_method(mrb, mrb->proc_class, "arity", mrb_proc_arity, MRB_ARGS_NONE());
+  mrb_define_method(mrb, mrb->proc_class, "arity", proc_arity, MRB_ARGS_NONE());
 
   p = mrb_proc_new(mrb, call_irep);
   MRB_METHOD_FROM_PROC(m, p);
   mrb_define_method_raw(mrb, mrb->proc_class, mrb_intern_lit(mrb, "call"), m);
   mrb_define_method_raw(mrb, mrb->proc_class, mrb_intern_lit(mrb, "[]"), m);
 
-  mrb_define_class_method(mrb, mrb->kernel_module, "lambda", proc_lambda, MRB_ARGS_NONE()); /* 15.3.1.2.6  */
-  mrb_define_method(mrb, mrb->kernel_module,       "lambda", proc_lambda, MRB_ARGS_NONE()); /* 15.3.1.3.27 */
+  mrb_define_class_method(mrb, mrb->kernel_module, "lambda", proc_lambda, MRB_ARGS_NONE()|MRB_ARGS_BLOCK()); /* 15.3.1.2.6  */
+  mrb_define_method(mrb, mrb->kernel_module,       "lambda", proc_lambda, MRB_ARGS_NONE()|MRB_ARGS_BLOCK()); /* 15.3.1.3.27 */
 }
diff --git a/src/range.c b/src/range.c
index 0360b48ae..c9dfb2b3c 100644
--- a/src/range.c
+++ b/src/range.c
@@ -10,19 +10,12 @@
 #include <mruby/string.h>
 #include <mruby/array.h>
 
-MRB_API struct RRange*
-mrb_range_ptr(mrb_state *mrb, mrb_value v)
-{
-  struct RRange *r = (struct RRange*)mrb_ptr(v);
-
-  if (r->edges == NULL) {
-    mrb_raise(mrb, E_ARGUMENT_ERROR, "uninitialized range");
-  }
-  return r;
-}
+#define RANGE_INITIALIZED_MASK 1
+#define RANGE_INITIALIZED(p) ((p)->flags |= RANGE_INITIALIZED_MASK)
+#define RANGE_INITIALIZED_P(p) ((p)->flags & RANGE_INITIALIZED_MASK)
 
 static void
-range_check(mrb_state *mrb, mrb_value a, mrb_value b)
+r_check(mrb_state *mrb, mrb_value a, mrb_value b)
 {
   mrb_value ans;
   enum mrb_vtype ta;
@@ -46,18 +39,83 @@ range_check(mrb_state *mrb, mrb_value a, mrb_value b)
   }
 }
 
-MRB_API mrb_value
-mrb_range_new(mrb_state *mrb, mrb_value beg, mrb_value end, mrb_bool excl)
+static mrb_bool
+r_le(mrb_state *mrb, mrb_value a, mrb_value b)
 {
-  struct RRange *r;
+  mrb_value r = mrb_funcall(mrb, a, "<=>", 1, b); /* compare result */
+  /* output :a < b => -1, a = b =>  0, a > b => +1 */
 
-  range_check(mrb, beg, end);
-  r = (struct RRange*)mrb_obj_alloc(mrb, MRB_TT_RANGE, mrb->range_class);
+  if (mrb_fixnum_p(r)) {
+    mrb_int c = mrb_fixnum(r);
+    if (c == 0 || c == -1) return TRUE;
+  }
+
+  return FALSE;
+}
+
+static mrb_bool
+r_gt(mrb_state *mrb, mrb_value a, mrb_value b)
+{
+  mrb_value r = mrb_funcall(mrb, a, "<=>", 1, b);
+  /* output :a < b => -1, a = b =>  0, a > b => +1 */
+
+  return mrb_fixnum_p(r) && mrb_fixnum(r) == 1;
+}
+
+static mrb_bool
+r_ge(mrb_state *mrb, mrb_value a, mrb_value b)
+{
+  mrb_value r = mrb_funcall(mrb, a, "<=>", 1, b); /* compare result */
+  /* output :a < b => -1, a = b =>  0, a > b => +1 */
+
+  if (mrb_fixnum_p(r)) {
+    mrb_int c = mrb_fixnum(r);
+    if (c == 0 || c == 1) return TRUE;
+  }
+
+  return FALSE;
+}
+
+static void
+range_ptr_alloc_edges(mrb_state *mrb, struct RRange *r)
+{
+#ifndef MRB_RANGE_EMBED
   r->edges = (mrb_range_edges *)mrb_malloc(mrb, sizeof(mrb_range_edges));
-  r->edges->beg = beg;
-  r->edges->end = end;
-  r->excl = excl;
-  return mrb_range_value(r);
+#endif
+}
+
+static struct RRange *
+range_ptr_init(mrb_state *mrb, struct RRange *r, mrb_value beg, mrb_value end, mrb_bool excl)
+{
+  r_check(mrb, beg, end);
+
+  if (r) {
+    if (RANGE_INITIALIZED_P(r)) {
+      /* Ranges are immutable, so that they should be initialized only once. */
+      mrb_name_error(mrb, mrb_intern_lit(mrb, "initialize"), "'initialize' called twice");
+    }
+    else {
+      range_ptr_alloc_edges(mrb, r);
+    }
+  }
+  else {
+    r = (struct RRange*)mrb_obj_alloc(mrb, MRB_TT_RANGE, mrb->range_class);
+    range_ptr_alloc_edges(mrb, r);
+  }
+
+  RANGE_BEG(r) = beg;
+  RANGE_END(r) = end;
+  RANGE_EXCL(r) = excl;
+  RANGE_INITIALIZED(r);
+
+  return r;
+}
+
+static void
+range_ptr_replace(mrb_state *mrb, struct RRange *r, mrb_value beg, mrb_value end, mrb_bool excl)
+{
+  range_ptr_init(mrb, r, beg, end, excl);
+  mrb_write_barrier(mrb, (struct RBasic*)r);
 }
 
 /*
@@ -67,12 +125,10 @@ mrb_range_new(mrb_state *mrb, mrb_value beg, mrb_value end, mrb_bool excl)
  *
  *  Returns the first object in <i>rng</i>.
  */
-mrb_value
-mrb_range_beg(mrb_state *mrb, mrb_value range)
+static mrb_value
+range_beg(mrb_state *mrb, mrb_value range)
 {
-  struct RRange *r = mrb_range_ptr(mrb, range);
-
-  return r->edges->beg;
+  return mrb_range_beg(mrb, range);
 }
 
 /*
@@ -85,13 +141,10 @@ mrb_range_beg(mrb_state *mrb, mrb_value range)
  *     (1..10).end    #=> 10
  *     (1...10).end   #=> 10
  */
-
-mrb_value
-mrb_range_end(mrb_state *mrb, mrb_value range)
+static mrb_value
+range_end(mrb_state *mrb, mrb_value range)
 {
-  struct RRange *r = mrb_range_ptr(mrb, range);
-
-  return r->edges->end;
+  return mrb_range_end(mrb, range);
 }
 
 /*
@@ -100,27 +153,12 @@ mrb_range_end(mrb_state *mrb, mrb_value range)
  *
  *  Returns <code>true</code> if <i>range</i> excludes its end value.
  */
-mrb_value
-mrb_range_excl(mrb_state *mrb, mrb_value range)
+static mrb_value
+range_excl(mrb_state *mrb, mrb_value range)
 {
-  struct RRange *r = mrb_range_ptr(mrb, range);
-
-  return mrb_bool_value(r->excl);
+  return mrb_bool_value(mrb_range_excl_p(mrb, range));
 }
 
-static void
-range_init(mrb_state *mrb, mrb_value range, mrb_value beg, mrb_value end, mrb_bool exclude_end)
-{
-  struct RRange *r = mrb_range_raw_ptr(range);
-
-  range_check(mrb, beg, end);
-  r->excl = exclude_end;
-  if (!r->edges) {
-    r->edges = (mrb_range_edges *)mrb_malloc(mrb, sizeof(mrb_range_edges));
-  }
-  r->edges->beg = beg;
-  r->edges->end = end;
-}
 /*
  *  call-seq:
  *     Range.new(start, end, exclusive=false)    => range
@@ -129,25 +167,17 @@ range_init(mrb_state *mrb, mrb_value range, mrb_value beg, mrb_value end, mrb_bo
  *  parameter is omitted or is <code>false</code>, the <i>range</i> will include
  *  the end object; otherwise, it will be excluded.
  */
-
-mrb_value
-mrb_range_initialize(mrb_state *mrb, mrb_value range)
+static mrb_value
+range_initialize(mrb_state *mrb, mrb_value range)
 {
   mrb_value beg, end;
-  mrb_bool exclusive;
-  mrb_int n;
+  mrb_bool exclusive = FALSE;
 
-  n = mrb_get_args(mrb, "oo|b", &beg, &end, &exclusive);
-  if (n != 3) {
-    exclusive = FALSE;
-  }
-  /* Ranges are immutable, so that they should be initialized only once. */
-  if (mrb_range_raw_ptr(range)->edges) {
-    mrb_name_error(mrb, mrb_intern_lit(mrb, "initialize"), "`initialize' called twice");
-  }
-  range_init(mrb, range, beg, end, exclusive);
+  mrb_get_args(mrb, "oo|b", &beg, &end, &exclusive);
+  range_ptr_replace(mrb, mrb_range_raw_ptr(range), beg, end, exclusive);
   return range;
 }
+
 /*
  *  call-seq:
  *     range == obj    => true or false
@@ -160,11 +190,9 @@ mrb_range_initialize(mrb_state *mrb, mrb_value range)
  *    (0..2) == (0..2)            #=> true
  *    (0..2) == Range.new(0,2)    #=> true
  *    (0..2) == (0...2)           #=> false
- *
  */
-
-mrb_value
-mrb_range_eq(mrb_state *mrb, mrb_value range)
+static mrb_value
+range_eq(mrb_state *mrb, mrb_value range)
 {
   struct RRange *rr;
   struct RRange *ro;
@@ -179,60 +207,22 @@ mrb_range_eq(mrb_state *mrb, mrb_value range)
 
   rr = mrb_range_ptr(mrb, range);
   ro = mrb_range_ptr(mrb, obj);
-  v1 = mrb_funcall(mrb, rr->edges->beg, "==", 1, ro->edges->beg);
-  v2 = mrb_funcall(mrb, rr->edges->end, "==", 1, ro->edges->end);
-  if (!mrb_bool(v1) || !mrb_bool(v2) || rr->excl != ro->excl) {
+  v1 = mrb_funcall(mrb, RANGE_BEG(rr), "==", 1, RANGE_BEG(ro));
+  v2 = mrb_funcall(mrb, RANGE_END(rr), "==", 1, RANGE_END(ro));
+  if (!mrb_bool(v1) || !mrb_bool(v2) || RANGE_EXCL(rr) != RANGE_EXCL(ro)) {
     return mrb_false_value();
   }
   return mrb_true_value();
 }
 
-static mrb_bool
-r_le(mrb_state *mrb, mrb_value a, mrb_value b)
-{
-  mrb_value r = mrb_funcall(mrb, a, "<=>", 1, b); /* compare result */
-  /* output :a < b => -1, a = b =>  0, a > b => +1 */
-
-  if (mrb_fixnum_p(r)) {
-    mrb_int c = mrb_fixnum(r);
-    if (c == 0 || c == -1) return TRUE;
-  }
-
-  return FALSE;
-}
-
-static mrb_bool
-r_gt(mrb_state *mrb, mrb_value a, mrb_value b)
-{
-  mrb_value r = mrb_funcall(mrb, a, "<=>", 1, b);
-  /* output :a < b => -1, a = b =>  0, a > b => +1 */
-
-  return mrb_fixnum_p(r) && mrb_fixnum(r) == 1;
-}
-
-static mrb_bool
-r_ge(mrb_state *mrb, mrb_value a, mrb_value b)
-{
-  mrb_value r = mrb_funcall(mrb, a, "<=>", 1, b); /* compare result */
-  /* output :a < b => -1, a = b =>  0, a > b => +1 */
-
-  if (mrb_fixnum_p(r)) {
-    mrb_int c = mrb_fixnum(r);
-    if (c == 0 || c == 1) return TRUE;
-  }
-
-  return FALSE;
-}
-
 /*
  *  call-seq:
  *     range === obj       =>  true or false
  *     range.member?(val)  =>  true or false
  *     range.include?(val) =>  true or false
- *
  */
-mrb_value
-mrb_range_include(mrb_state *mrb, mrb_value range)
+static mrb_value
+range_include(mrb_state *mrb, mrb_value range)
 {
   mrb_value val;
   struct RRange *r = mrb_range_ptr(mrb, range);
@@ -241,48 +231,15 @@ mrb_range_include(mrb_state *mrb, mrb_value range)
 
   mrb_get_args(mrb, "o", &val);
 
-  beg = r->edges->beg;
-  end = r->edges->end;
-  include_p = r_le(mrb, beg, val) &&           /* beg <= val */
-              (r->excl ? r_gt(mrb, end, val)   /* end >  val */
-                       : r_ge(mrb, end, val)); /* end >= val */
+  beg = RANGE_BEG(r);
+  end = RANGE_END(r);
+  include_p = r_le(mrb, beg, val) &&                 /* beg <= val */
+              (RANGE_EXCL(r) ? r_gt(mrb, end, val)   /* end >  val */
+                             : r_ge(mrb, end, val)); /* end >= val */
 
   return mrb_bool_value(include_p);
 }
 
-MRB_API mrb_int
-mrb_range_beg_len(mrb_state *mrb, mrb_value range, mrb_int *begp, mrb_int *lenp, mrb_int len, mrb_bool trunc)
-{
-  mrb_int beg, end;
-  struct RRange *r;
-
-  if (mrb_type(range) != MRB_TT_RANGE) return 0;
-  r = mrb_range_ptr(mrb, range);
-
-  beg = mrb_int(mrb, r->edges->beg);
-  end = mrb_int(mrb, r->edges->end);
-
-  if (beg < 0) {
-    beg += len;
-    if (beg < 0) return 2;
-  }
-
-  if (trunc) {
-    if (beg > len) return 2;
-    if (end > len) end = len;
-  }
-
-  if (end < 0) end += len;
-  if (!r->excl && (!trunc || end < len))
-    end++;                      /* include end point */
-  len = end - beg;
-  if (len < 0) len = 0;
-
-  *begp = beg;
-  *lenp = len;
-  return 1;
-}
-
 /* 15.2.14.4.12(x) */
 /*
  * call-seq:
@@ -290,17 +247,16 @@ mrb_range_beg_len(mrb_state *mrb, mrb_value range, mrb_int *begp, mrb_int *lenp,
  *
  * Convert this range object to a printable form.
  */
-
 static mrb_value
 range_to_s(mrb_state *mrb, mrb_value range)
 {
   mrb_value str, str2;
   struct RRange *r = mrb_range_ptr(mrb, range);
 
-  str  = mrb_obj_as_string(mrb, r->edges->beg);
-  str2 = mrb_obj_as_string(mrb, r->edges->end);
+  str  = mrb_obj_as_string(mrb, RANGE_BEG(r));
+  str2 = mrb_obj_as_string(mrb, RANGE_END(r));
   str  = mrb_str_dup(mrb, str);
-  mrb_str_cat(mrb, str, "...", r->excl ? 3 : 2);
+  mrb_str_cat(mrb, str, "...", RANGE_EXCL(r) ? 3 : 2);
   mrb_str_cat_str(mrb, str, str2);
 
   return str;
@@ -315,17 +271,16 @@ range_to_s(mrb_state *mrb, mrb_value range)
  * <code>inspect</code> to convert the start and end
  * objects).
  */
-
 static mrb_value
 range_inspect(mrb_state *mrb, mrb_value range)
 {
   mrb_value str, str2;
   struct RRange *r = mrb_range_ptr(mrb, range);
 
-  str  = mrb_inspect(mrb, r->edges->beg);
-  str2 = mrb_inspect(mrb, r->edges->end);
+  str  = mrb_inspect(mrb, RANGE_BEG(r));
+  str2 = mrb_inspect(mrb, RANGE_END(r));
   str  = mrb_str_dup(mrb, str);
-  mrb_str_cat(mrb, str, "...", r->excl ? 3 : 2);
+  mrb_str_cat(mrb, str, "...", RANGE_EXCL(r) ? 3 : 2);
   mrb_str_cat_str(mrb, str, str2);
 
   return str;
@@ -343,9 +298,7 @@ range_inspect(mrb_state *mrb, mrb_value range)
  *    (0..2).eql?(0..2)            #=> true
  *    (0..2).eql?(Range.new(0,2))  #=> true
  *    (0..2).eql?(0...2)           #=> false
- *
  */
-
 static mrb_value
 range_eql(mrb_state *mrb, mrb_value range)
 {
@@ -355,16 +308,14 @@ range_eql(mrb_state *mrb, mrb_value range)
   mrb_get_args(mrb, "o", &obj);
 
   if (mrb_obj_equal(mrb, range, obj)) return mrb_true_value();
-  if (!mrb_obj_is_kind_of(mrb, obj, mrb->range_class)) {
-    return mrb_false_value();
-  }
+  if (!mrb_obj_is_kind_of(mrb, obj, mrb->range_class)) return mrb_false_value();
   if (mrb_type(obj) != MRB_TT_RANGE) return mrb_false_value();
 
   r = mrb_range_ptr(mrb, range);
   o = mrb_range_ptr(mrb, obj);
-  if (!mrb_eql(mrb, r->edges->beg, o->edges->beg) ||
-      !mrb_eql(mrb, r->edges->end, o->edges->end) ||
-      (r->excl != o->excl)) {
+  if (!mrb_eql(mrb, RANGE_BEG(r), RANGE_BEG(o)) ||
+      !mrb_eql(mrb, RANGE_END(r), RANGE_END(o)) ||
+      (RANGE_EXCL(r) != RANGE_EXCL(o))) {
     return mrb_false_value();
   }
   return mrb_true_value();
@@ -385,7 +336,7 @@ range_initialize_copy(mrb_state *mrb, mrb_value copy)
   }
 
   r = mrb_range_ptr(mrb, src);
-  range_init(mrb, copy, r->edges->beg, r->edges->end, r->excl);
+  range_ptr_replace(mrb, mrb_range_raw_ptr(copy), RANGE_BEG(r), RANGE_END(r), RANGE_EXCL(r));
 
   return copy;
 }
@@ -401,7 +352,7 @@ mrb_get_values_at(mrb_state *mrb, mrb_value obj, mrb_int olen, mrb_int argc, con
     if (mrb_fixnum_p(argv[i])) {
       mrb_ary_push(mrb, result, func(mrb, obj, mrb_fixnum(argv[i])));
     }
-    else if (mrb_range_beg_len(mrb, argv[i], &beg, &len, olen, FALSE) == 1) {
+    else if (mrb_range_beg_len(mrb, argv[i], &beg, &len, olen, FALSE) == MRB_RANGE_OK) {
       mrb_int const end = olen < beg + len ? olen : beg + len;
       for (j = beg; j < end; ++j) {
         mrb_ary_push(mrb, result, func(mrb, obj, j));
@@ -420,6 +371,66 @@ mrb_get_values_at(mrb_state *mrb, mrb_value obj, mrb_int olen, mrb_int argc, con
 }
 
 void
+mrb_gc_mark_range(mrb_state *mrb, struct RRange *r)
+{
+  if (RANGE_INITIALIZED_P(r)) {
+    mrb_gc_mark_value(mrb, RANGE_BEG(r));
+    mrb_gc_mark_value(mrb, RANGE_END(r));
+  }
+}
+
+MRB_API struct RRange*
+mrb_range_ptr(mrb_state *mrb, mrb_value range)
+{
+  struct RRange *r = mrb_range_raw_ptr(range);
+
+  /* check for if #initialize_copy was removed [#3320] */
+  if (!RANGE_INITIALIZED_P(r)) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "uninitialized range");
+  }
+  return r;
+}
+
+MRB_API mrb_value
+mrb_range_new(mrb_state *mrb, mrb_value beg, mrb_value end, mrb_bool excl)
+{
+  struct RRange *r = range_ptr_init(mrb, NULL, beg, end, excl);
+  return mrb_range_value(r);
+}
+
+MRB_API enum mrb_range_beg_len
+mrb_range_beg_len(mrb_state *mrb, mrb_value range, mrb_int *begp, mrb_int *lenp, mrb_int len, mrb_bool trunc)
+{
+  mrb_int beg, end;
+  struct RRange *r;
+
+  if (mrb_type(range) != MRB_TT_RANGE) return MRB_RANGE_TYPE_MISMATCH;
+  r = mrb_range_ptr(mrb, range);
+
+  beg = mrb_int(mrb, RANGE_BEG(r));
+  end = mrb_int(mrb, RANGE_END(r));
+
+  if (beg < 0) {
+    beg += len;
+    if (beg < 0) return MRB_RANGE_OUT;
+  }
+
+  if (trunc) {
+    if (beg > len) return MRB_RANGE_OUT;
+    if (end > len) end = len;
+  }
+
+  if (end < 0) end += len;
+  if (!RANGE_EXCL(r) && (!trunc || end < len)) end++;  /* include end point */
+  len = end - beg;
+  if (len < 0) len = 0;
+
+  *begp = beg;
+  *lenp = len;
+  return MRB_RANGE_OK;
+}
+
+void
 mrb_init_range(mrb_state *mrb)
 {
   struct RClass *r;
@@ -428,17 +439,16 @@ mrb_init_range(mrb_state *mrb)
   mrb->range_class = r;
   MRB_SET_INSTANCE_TT(r, MRB_TT_RANGE);
 
-  mrb_define_method(mrb, r, "begin",           mrb_range_beg,         MRB_ARGS_NONE()); /* 15.2.14.4.3  */
-  mrb_define_method(mrb, r, "end",             mrb_range_end,         MRB_ARGS_NONE()); /* 15.2.14.4.5  */
-  mrb_define_method(mrb, r, "==",              mrb_range_eq,          MRB_ARGS_REQ(1)); /* 15.2.14.4.1  */
-  mrb_define_method(mrb, r, "===",             mrb_range_include,     MRB_ARGS_REQ(1)); /* 15.2.14.4.2  */
-  mrb_define_method(mrb, r, "exclude_end?",    mrb_range_excl,        MRB_ARGS_NONE()); /* 15.2.14.4.6  */
-  mrb_define_method(mrb, r, "first",           mrb_range_beg,         MRB_ARGS_NONE()); /* 15.2.14.4.7  */
-  mrb_define_method(mrb, r, "include?",        mrb_range_include,     MRB_ARGS_REQ(1)); /* 15.2.14.4.8  */
-  mrb_define_method(mrb, r, "initialize",      mrb_range_initialize,  MRB_ARGS_ANY());  /* 15.2.14.4.9  */
-  mrb_define_method(mrb, r, "last",            mrb_range_end,         MRB_ARGS_NONE()); /* 15.2.14.4.10 */
-  mrb_define_method(mrb, r, "member?",         mrb_range_include,     MRB_ARGS_REQ(1)); /* 15.2.14.4.11 */
-
+  mrb_define_method(mrb, r, "begin",           range_beg,             MRB_ARGS_NONE()); /* 15.2.14.4.3  */
+  mrb_define_method(mrb, r, "end",             range_end,             MRB_ARGS_NONE()); /* 15.2.14.4.5  */
+  mrb_define_method(mrb, r, "==",              range_eq,              MRB_ARGS_REQ(1)); /* 15.2.14.4.1  */
+  mrb_define_method(mrb, r, "===",             range_include,         MRB_ARGS_REQ(1)); /* 15.2.14.4.2  */
+  mrb_define_method(mrb, r, "exclude_end?",    range_excl,            MRB_ARGS_NONE()); /* 15.2.14.4.6  */
+  mrb_define_method(mrb, r, "first",           range_beg,             MRB_ARGS_NONE()); /* 15.2.14.4.7  */
+  mrb_define_method(mrb, r, "include?",        range_include,         MRB_ARGS_REQ(1)); /* 15.2.14.4.8  */
+  mrb_define_method(mrb, r, "initialize",      range_initialize,      MRB_ARGS_ANY());  /* 15.2.14.4.9  */
+  mrb_define_method(mrb, r, "last",            range_end,             MRB_ARGS_NONE()); /* 15.2.14.4.10 */
+  mrb_define_method(mrb, r, "member?",         range_include,         MRB_ARGS_REQ(1)); /* 15.2.14.4.11 */
   mrb_define_method(mrb, r, "to_s",            range_to_s,            MRB_ARGS_NONE()); /* 15.2.14.4.12(x) */
   mrb_define_method(mrb, r, "inspect",         range_inspect,         MRB_ARGS_NONE()); /* 15.2.14.4.13(x) */
   mrb_define_method(mrb, r, "eql?",            range_eql,             MRB_ARGS_REQ(1)); /* 15.2.14.4.14(x) */
diff --git a/src/state.c b/src/state.c
index 18d104555..c42df71ba 100644
--- a/src/state.c
+++ b/src/state.c
@@ -26,6 +26,7 @@ mrb_open_core(mrb_allocf f, void *ud)
   static const struct mrb_context mrb_context_zero = { 0 };
   mrb_state *mrb;
 
+  if (f == NULL) f = mrb_default_allocf;
   mrb = (mrb_state *)(f)(NULL, NULL, sizeof(mrb_state), ud);
   if (mrb == NULL) return NULL;
 
@@ -56,38 +57,6 @@ mrb_default_allocf(mrb_state *mrb, void *p, size_t size, void *ud)
   }
 }
 
-struct alloca_header {
-  struct alloca_header *next;
-  char buf[1];
-};
-
-MRB_API void*
-mrb_alloca(mrb_state *mrb, size_t size)
-{
-  struct alloca_header *p;
-
-  p = (struct alloca_header*) mrb_malloc(mrb, sizeof(struct alloca_header)+size);
-  p->next = mrb->mems;
-  mrb->mems = p;
-  return (void*)p->buf;
-}
-
-static void
-mrb_alloca_free(mrb_state *mrb)
-{
-  struct alloca_header *p;
-  struct alloca_header *tmp;
-
-  if (mrb == NULL) return;
-  p = mrb->mems;
-
-  while (p) {
-    tmp = p;
-    p = p->next;
-    mrb_free(mrb, tmp);
-  }
-}
-
 MRB_API mrb_state*
 mrb_open(void)
 {
@@ -168,10 +137,6 @@ mrb_irep_free(mrb_state *mrb, mrb_irep *irep)
   }
   mrb_free(mrb, irep->reps);
   mrb_free(mrb, irep->lv);
-  if (irep->own_filename) {
-    mrb_free(mrb, (void *)irep->filename);
-  }
-  mrb_free(mrb, irep->lines);
   mrb_debug_info_free(mrb, irep->debug_info);
   mrb_free(mrb, irep);
 }
@@ -259,7 +224,6 @@ mrb_close(mrb_state *mrb)
   mrb_gc_free_gv(mrb);
   mrb_free_context(mrb, mrb->root_c);
   mrb_free_symtbl(mrb);
-  mrb_alloca_free(mrb);
   mrb_gc_destroy(mrb, &mrb->gc);
   mrb_free(mrb, mrb);
 }
@@ -273,7 +237,6 @@ mrb_add_irep(mrb_state *mrb)
   irep = (mrb_irep *)mrb_malloc(mrb, sizeof(mrb_irep));
   *irep = mrb_irep_zero;
   irep->refcnt = 1;
-  irep->own_filename = FALSE;
 
   return irep;
 }
diff --git a/src/string.c b/src/string.c
index 5cca6d460..6b7cced13 100644
--- a/src/string.c
+++ b/src/string.c
@@ -20,6 +20,7 @@
 #include <mruby/class.h>
 #include <mruby/range.h>
 #include <mruby/string.h>
+#include <mruby/numeric.h>
 #include <mruby/re.h>
 
 typedef struct mrb_shared_string {
@@ -82,7 +83,7 @@ str_new(mrb_state *mrb, const char *p, size_t len)
 }
 
 static inline void
-str_with_class(mrb_state *mrb, struct RString *s, mrb_value obj)
+str_with_class(struct RString *s, mrb_value obj)
 {
   s->c = mrb_str_ptr(obj)->c;
 }
@@ -92,7 +93,7 @@ mrb_str_new_empty(mrb_state *mrb, mrb_value str)
 {
   struct RString *s = str_new(mrb, 0, 0);
 
-  str_with_class(mrb, s, str);
+  str_with_class(s, str);
   return mrb_obj_value(s);
 }
 
@@ -156,13 +157,6 @@ mrb_str_new(mrb_state *mrb, const char *p, size_t len)
   return mrb_obj_value(str_new(mrb, p, len));
 }
 
-/*
- *  call-seq: (Caution! NULL string)
- *     String.new(str="")   => new_str
- *
- *  Returns a new string object containing a copy of <i>str</i>.
- */
-
 MRB_API mrb_value
 mrb_str_new_cstr(mrb_state *mrb, const char *p)
 {
@@ -200,6 +194,15 @@ str_decref(mrb_state *mrb, mrb_shared_string *shared)
   }
 }
 
+static void
+check_null_byte(mrb_state *mrb, mrb_value str)
+{
+  mrb_to_str(mrb, str);
+  if (memchr(RSTRING_PTR(str), '\0', RSTRING_LEN(str))) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "string contains null byte");
+  }
+}
+
 void
 mrb_gc_free_str(mrb_state *mrb, struct RString *str)
 {
@@ -230,35 +233,47 @@ utf8len(const char* p, const char* e)
   mrb_int len;
   mrb_int i;
 
+  if ((unsigned char)*p < 0x80) return 1;
   len = utf8len_codepage[(unsigned char)*p];
-  if (p + len > e) return 1;
+  if (len == 1) return 1;
+  if (len > e - p) return 1;
   for (i = 1; i < len; ++i)
     if ((p[i] & 0xc0) != 0x80)
       return 1;
   return len;
 }
 
-static mrb_int
-utf8_strlen(mrb_value str, mrb_int len)
+mrb_int
+mrb_utf8_len(const char *str, mrb_int byte_len)
 {
   mrb_int total = 0;
-  char* p = RSTRING_PTR(str);
-  char* e = p;
-  if (RSTRING(str)->flags & MRB_STR_NO_UTF) {
-    return RSTRING_LEN(str);
-  }
-  e += len < 0 ? RSTRING_LEN(str) : len;
-  while (p<e) {
+  const char *p = str;
+  const char *e = p + byte_len;
+
+  while (p < e) {
     p += utf8len(p, e);
     total++;
   }
-  if (RSTRING_LEN(str) == total) {
-    RSTRING(str)->flags |= MRB_STR_NO_UTF;
-  }
   return total;
 }
 
-#define RSTRING_CHAR_LEN(s) utf8_strlen(s, -1)
+static mrb_int
+utf8_strlen(mrb_value str)
+{
+  struct RString *s = mrb_str_ptr(str);
+  mrb_int byte_len = RSTR_LEN(s);
+
+  if (RSTR_ASCII_P(s)) {
+    return byte_len;
+  }
+  else {
+    mrb_int utf8_len = mrb_utf8_len(RSTR_PTR(s), byte_len);
+    if (byte_len == utf8_len) RSTR_SET_ASCII_FLAG(s);
+    return utf8_len;
+  }
+}
+
+#define RSTRING_CHAR_LEN(s) utf8_strlen(s)
 
 /* map character index to byte offset index */
 static mrb_int
@@ -291,12 +306,71 @@ bytes2chars(char *p, mrb_int bi)
   return i;
 }
 
+static mrb_int
+str_index_str_by_char_search(mrb_state *mrb, const char *p, const char *pend, const char *s, const mrb_int slen, mrb_int off)
+{
+  /* Based on Quick Search algorithm (Boyer-Moore-Horspool algorithm) */
+
+  ptrdiff_t qstable[1 << CHAR_BIT];
+
+  /* Preprocessing */
+  {
+    mrb_int i;
+
+    for (i = 0; i < 1 << CHAR_BIT; i ++) {
+      qstable[i] = slen;
+    }
+    for (i = 0; i < slen; i ++) {
+      qstable[(unsigned char)s[i]] = slen - (i + 1);
+    }
+  }
+
+  /* Searching */
+  while (p < pend && pend - p >= slen) {
+    const char *pivot;
+
+    if (memcmp(p, s, slen) == 0) {
+      return off;
+    }
+
+    pivot = p + qstable[(unsigned char)p[slen - 1]];
+    if (pivot > pend || pivot < p /* overflowed */) { return -1; }
+
+    do {
+      p += utf8len(p, pend);
+      off ++;
+    } while (p < pivot);
+  }
+
+  return -1;
+}
+
+static mrb_int
+str_index_str_by_char(mrb_state *mrb, mrb_value str, mrb_value sub, mrb_int pos)
+{
+  const char *p = RSTRING_PTR(str);
+  const char *pend = p + RSTRING_LEN(str);
+  const char *s = RSTRING_PTR(sub);
+  const mrb_int slen = RSTRING_LEN(sub);
+  mrb_int off = pos;
+
+  for (; pos > 0; pos --) {
+    if (pend - p < 1) { return -1; }
+    p += utf8len(p, pend);
+  }
+
+  if (slen < 1) { return off; }
+
+  return str_index_str_by_char_search(mrb, p, pend, s, slen, off);
+}
+
 #define BYTES_ALIGN_CHECK(pos) if (pos < 0) return mrb_nil_value();
 #else
 #define RSTRING_CHAR_LEN(s) RSTRING_LEN(s)
 #define chars2bytes(p, off, ci) (ci)
 #define bytes2chars(p, bi) (bi)
 #define BYTES_ALIGN_CHECK(pos)
+#define str_index_str_by_char(mrb, str, sub, pos) str_index_str(mrb, str, sub, pos)
 #endif
 
 static inline mrb_int
@@ -398,8 +472,8 @@ str_make_shared(mrb_state *mrb, struct RString *orig, struct RString *s)
   }
 }
 
-static mrb_value
-byte_subseq(mrb_state *mrb, mrb_value str, mrb_int beg, mrb_int len)
+mrb_value
+mrb_str_byte_subseq(mrb_state *mrb, mrb_value str, mrb_int beg, mrb_int len)
 {
   struct RString *orig, *s;
 
@@ -413,44 +487,48 @@ byte_subseq(mrb_state *mrb, mrb_value str, mrb_int beg, mrb_int len)
     s->as.heap.ptr += beg;
     s->as.heap.len = len;
   }
+  RSTR_COPY_ASCII_FLAG(s, orig);
   return mrb_obj_value(s);
 }
+
+static void
+str_range_to_bytes(mrb_value str, mrb_int *pos, mrb_int *len)
+{
+  *pos = chars2bytes(str, 0, *pos);
+  *len = chars2bytes(str, *pos, *len);
+}
 #ifdef MRB_UTF8_STRING
 static inline mrb_value
 str_subseq(mrb_state *mrb, mrb_value str, mrb_int beg, mrb_int len)
 {
-  beg = chars2bytes(str, 0, beg);
-  len = chars2bytes(str, beg, len);
-
-  return byte_subseq(mrb, str, beg, len);
+  str_range_to_bytes(str, &beg, &len);
+  return mrb_str_byte_subseq(mrb, str, beg, len);
 }
 #else
-#define str_subseq(mrb, str, beg, len) byte_subseq(mrb, str, beg, len)
+#define str_subseq(mrb, str, beg, len) mrb_str_byte_subseq(mrb, str, beg, len)
 #endif
 
-static mrb_value
-str_substr(mrb_state *mrb, mrb_value str, mrb_int beg, mrb_int len)
+mrb_bool
+mrb_str_beg_len(mrb_int str_len, mrb_int *begp, mrb_int *lenp)
 {
-  mrb_int clen = RSTRING_CHAR_LEN(str);
-
-  if (len < 0) return mrb_nil_value();
-  if (clen == 0) {
-    len = 0;
-  }
-  else if (beg < 0) {
-    beg = clen + beg;
-  }
-  if (beg > clen) return mrb_nil_value();
-  if (beg < 0) {
-    beg += clen;
-    if (beg < 0) return mrb_nil_value();
+  if (str_len < *begp || *lenp < 0) return FALSE;
+  if (*begp < 0) {
+    *begp += str_len;
+    if (*begp < 0) return FALSE;
   }
-  if (len > clen - beg)
-    len = clen - beg;
-  if (len <= 0) {
-    len = 0;
+  if (*lenp > str_len - *begp)
+    *lenp = str_len - *begp;
+  if (*lenp <= 0) {
+    *lenp = 0;
   }
-  return str_subseq(mrb, str, beg, len);
+  return TRUE;
+}
+
+static mrb_value
+str_substr(mrb_state *mrb, mrb_value str, mrb_int beg, mrb_int len)
+{
+  return mrb_str_beg_len(RSTRING_CHAR_LEN(str), &beg, &len) ?
+    str_subseq(mrb, str, beg, len) : mrb_nil_value();
 }
 
 MRB_API mrb_int
@@ -490,23 +568,14 @@ str_index_str(mrb_state *mrb, mrb_value str, mrb_value str2, mrb_int offset)
   return mrb_str_index(mrb, str, ptr, len, offset);
 }
 
-static void
-check_frozen(mrb_state *mrb, struct RString *s)
-{
-  if (MRB_FROZEN_P(s)) {
-    mrb_raise(mrb, E_FROZEN_ERROR, "can't modify frozen string");
-  }
-}
-
 static mrb_value
 str_replace(mrb_state *mrb, struct RString *s1, struct RString *s2)
 {
   mrb_int len;
 
-  check_frozen(mrb, s1);
+  mrb_check_frozen(mrb, s1);
   if (s1 == s2) return mrb_obj_value(s1);
-  s1->flags &= ~MRB_STR_NO_UTF;
-  s1->flags |= s2->flags&MRB_STR_NO_UTF;
+  RSTR_COPY_ASCII_FLAG(s1, s2);
   len = RSTR_LEN(s2);
   if (RSTR_SHARED_P(s1)) {
     str_decref(mrb, s1->as.heap.aux.shared);
@@ -641,10 +710,9 @@ mrb_locale_from_utf8(const char *utf8, int len)
 #endif
 
 MRB_API void
-mrb_str_modify(mrb_state *mrb, struct RString *s)
+mrb_str_modify_keep_ascii(mrb_state *mrb, struct RString *s)
 {
-  check_frozen(mrb, s);
-  s->flags &= ~MRB_STR_NO_UTF;
+  mrb_check_frozen(mrb, s);
   if (RSTR_SHARED_P(s)) {
     mrb_shared_string *shared = s->as.heap.aux.shared;
 
@@ -708,6 +776,9 @@ mrb_str_resize(mrb_state *mrb, mrb_value str, mrb_int len)
   mrb_int slen;
   struct RString *s = mrb_str_ptr(str);
 
+  if (len < 0) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "negative (or overflowed) string size");
+  }
   mrb_str_modify(mrb, s);
   slen = RSTR_LEN(s);
   if (len != slen) {
@@ -725,38 +796,18 @@ mrb_str_to_cstr(mrb_state *mrb, mrb_value str0)
 {
   struct RString *s;
 
-  if (!mrb_string_p(str0)) {
-    mrb_raise(mrb, E_TYPE_ERROR, "expected String");
-  }
-
+  check_null_byte(mrb, str0);
   s = str_new(mrb, RSTRING_PTR(str0), RSTRING_LEN(str0));
-  if ((strlen(RSTR_PTR(s)) ^ RSTR_LEN(s)) != 0) {
-    mrb_raise(mrb, E_ARGUMENT_ERROR, "string contains null byte");
-  }
   return RSTR_PTR(s);
 }
 
-/*
- *  call-seq: (Caution! String("abcd") change)
- *     String("abcdefg") = String("abcd") + String("efg")
- *
- *  Returns a new string object containing a copy of <i>str</i>.
- */
 MRB_API void
 mrb_str_concat(mrb_state *mrb, mrb_value self, mrb_value other)
 {
-  if (!mrb_string_p(other)) {
-    other = mrb_str_to_str(mrb, other);
-  }
+  other = mrb_str_to_str(mrb, other);
   mrb_str_cat_str(mrb, self, other);
 }
 
-/*
- *  call-seq: (Caution! String("abcd") remain)
- *     String("abcdefg") = String("abcd") + String("efg")
- *
- *  Returns a new string object containing a copy of <i>str</i>.
- */
 MRB_API mrb_value
 mrb_str_plus(mrb_state *mrb, mrb_value a, mrb_value b)
 {
@@ -774,10 +825,13 @@ mrb_str_plus(mrb_state *mrb, mrb_value a, mrb_value b)
 /* 15.2.10.5.2  */
 
 /*
- *  call-seq: (Caution! String("abcd") remain) for stack_argument
- *     String("abcdefg") = String("abcd") + String("efg")
+ *  call-seq:
+ *     str + other_str   -> new_str
  *
- *  Returns a new string object containing a copy of <i>str</i>.
+ *  Concatenation---Returns a new <code>String</code> containing
+ *  <i>other_str</i> concatenated to <i>str</i>.
+ *
+ *     "Hello from " + self.to_s   #=> "Hello from main"
  */
 static mrb_value
 mrb_str_plus_m(mrb_state *mrb, mrb_value self)
@@ -837,7 +891,7 @@ mrb_str_times(mrb_state *mrb, mrb_value self)
 
   len = RSTRING_LEN(self)*times;
   str2 = str_new(mrb, 0, len);
-  str_with_class(mrb, str2, self);
+  str_with_class(str2, self);
   p = RSTR_PTR(str2);
   if (len > 0) {
     n = RSTRING_LEN(self);
@@ -849,6 +903,7 @@ mrb_str_times(mrb_state *mrb, mrb_value self)
     memcpy(p + n, p, len-n);
   }
   p[RSTR_LEN(str2)] = '\0';
+  RSTR_COPY_ASCII_FLAG(str2, mrb_str_ptr(self));
 
   return mrb_obj_value(str2);
 }
@@ -953,15 +1008,7 @@ str_eql(mrb_state *mrb, const mrb_value str1, const mrb_value str2)
 MRB_API mrb_bool
 mrb_str_equal(mrb_state *mrb, mrb_value str1, mrb_value str2)
 {
-  if (mrb_immediate_p(str2)) return FALSE;
-  if (!mrb_string_p(str2)) {
-    if (mrb_nil_p(str2)) return FALSE;
-    if (!mrb_respond_to(mrb, str2, mrb_intern_lit(mrb, "to_str"))) {
-      return FALSE;
-    }
-    str2 = mrb_funcall(mrb, str2, "to_str", 0);
-    return mrb_equal(mrb, str2, str1);
-  }
+  if (!mrb_string_p(str2)) return FALSE;
   return str_eql(mrb, str1, str2);
 }
 
@@ -986,47 +1033,38 @@ mrb_str_equal_m(mrb_state *mrb, mrb_value str1)
   return mrb_bool_value(mrb_str_equal(mrb, str1, str2));
 }
 /* ---------------------------------- */
+mrb_value mrb_mod_to_s(mrb_state *mrb, mrb_value klass);
+
 MRB_API mrb_value
 mrb_str_to_str(mrb_state *mrb, mrb_value str)
 {
-  mrb_value s;
-
-  if (!mrb_string_p(str)) {
-    s = mrb_check_convert_type(mrb, str, MRB_TT_STRING, "String", "to_str");
-    if (mrb_nil_p(s)) {
-      s = mrb_convert_type(mrb, str, MRB_TT_STRING, "String", "to_s");
-    }
-    return s;
+  switch (mrb_type(str)) {
+  case MRB_TT_STRING:
+    return str;
+  case MRB_TT_SYMBOL:
+    return mrb_sym2str(mrb, mrb_symbol(str));
+  case MRB_TT_FIXNUM:
+    return mrb_fixnum_to_str(mrb, str, 10);
+  case MRB_TT_CLASS:
+  case MRB_TT_MODULE:
+    return mrb_mod_to_s(mrb, str);
+  default:
+    return mrb_convert_type(mrb, str, MRB_TT_STRING, "String", "to_s");
   }
-  return str;
 }
 
 MRB_API const char*
-mrb_string_value_ptr(mrb_state *mrb, mrb_value ptr)
+mrb_string_value_ptr(mrb_state *mrb, mrb_value str)
 {
-  mrb_value str = mrb_str_to_str(mrb, ptr);
+  str = mrb_str_to_str(mrb, str);
   return RSTRING_PTR(str);
 }
 
 MRB_API mrb_int
 mrb_string_value_len(mrb_state *mrb, mrb_value ptr)
 {
-  mrb_value str = mrb_str_to_str(mrb, ptr);
-  return RSTRING_LEN(str);
-}
-
-void
-mrb_noregexp(mrb_state *mrb, mrb_value self)
-{
-  mrb_raise(mrb, E_NOTIMP_ERROR, "Regexp class not implemented");
-}
-
-void
-mrb_regexp_check(mrb_state *mrb, mrb_value obj)
-{
-  if (mrb_regexp_p(mrb, obj)) {
-    mrb_noregexp(mrb, obj);
-  }
+  mrb_to_str(mrb, ptr);
+  return RSTRING_LEN(ptr);
 }
 
 MRB_API mrb_value
@@ -1035,56 +1073,95 @@ mrb_str_dup(mrb_state *mrb, mrb_value str)
   struct RString *s = mrb_str_ptr(str);
   struct RString *dup = str_new(mrb, 0, 0);
 
-  str_with_class(mrb, dup, str);
+  str_with_class(dup, str);
   return str_replace(mrb, dup, s);
 }
 
-static mrb_value
-mrb_str_aref(mrb_state *mrb, mrb_value str, mrb_value indx)
-{
-  mrb_int idx;
+enum str_convert_range {
+  /* `beg` and `len` are byte unit in `0 ... str.bytesize` */
+  STR_BYTE_RANGE_CORRECTED = 1,
 
-  mrb_regexp_check(mrb, indx);
-  switch (mrb_type(indx)) {
-    case MRB_TT_FIXNUM:
-      idx = mrb_fixnum(indx);
+  /* `beg` and `len` are char unit in any range */
+  STR_CHAR_RANGE = 2,
 
-num_index:
-      str = str_substr(mrb, str, idx, 1);
-      if (!mrb_nil_p(str) && RSTRING_LEN(str) == 0) return mrb_nil_value();
-      return str;
+  /* `beg` and `len` are char unit in `0 ... str.size` */
+  STR_CHAR_RANGE_CORRECTED = 3,
 
-    case MRB_TT_STRING:
-      if (str_index_str(mrb, str, indx, 0) != -1)
-        return mrb_str_dup(mrb, indx);
-      return mrb_nil_value();
+  /* `beg` is out of range */
+  STR_OUT_OF_RANGE = -1
+};
 
-    case MRB_TT_RANGE:
-      goto range_arg;
+static enum str_convert_range
+str_convert_range(mrb_state *mrb, mrb_value str, mrb_value indx, mrb_value alen, mrb_int *beg, mrb_int *len)
+{
+  if (!mrb_undef_p(alen)) {
+    *beg = mrb_int(mrb, indx);
+    *len = mrb_int(mrb, alen);
+    return STR_CHAR_RANGE;
+  }
+  else {
+    switch (mrb_type(indx)) {
+      case MRB_TT_FIXNUM:
+        *beg = mrb_fixnum(indx);
+        *len = 1;
+        return STR_CHAR_RANGE;
 
-    default:
-      indx = mrb_Integer(mrb, indx);
-      if (mrb_nil_p(indx)) {
-      range_arg:
-        {
-          mrb_int beg, len;
-
-          len = RSTRING_CHAR_LEN(str);
-          switch (mrb_range_beg_len(mrb, indx, &beg, &len, len, TRUE)) {
-          case 1:
-            return str_subseq(mrb, str, beg, len);
-          case 2:
-            return mrb_nil_value();
+      case MRB_TT_STRING:
+        *beg = str_index_str(mrb, str, indx, 0);
+        if (*beg < 0) { break; }
+        *len = RSTRING_LEN(indx);
+        return STR_BYTE_RANGE_CORRECTED;
+
+      case MRB_TT_RANGE:
+        goto range_arg;
+
+      default:
+        indx = mrb_to_int(mrb, indx);
+        if (mrb_fixnum_p(indx)) {
+          *beg = mrb_fixnum(indx);
+          *len = 1;
+          return STR_CHAR_RANGE;
+        }
+range_arg:
+        *len = RSTRING_CHAR_LEN(str);
+        switch (mrb_range_beg_len(mrb, indx, beg, len, *len, TRUE)) {
+          case MRB_RANGE_OK:
+            return STR_CHAR_RANGE_CORRECTED;
+          case MRB_RANGE_OUT:
+            return STR_OUT_OF_RANGE;
           default:
             break;
-          }
         }
+
         mrb_raise(mrb, E_TYPE_ERROR, "can't convert to Fixnum");
+    }
+  }
+  return STR_OUT_OF_RANGE;
+}
+
+static mrb_value
+mrb_str_aref(mrb_state *mrb, mrb_value str, mrb_value indx, mrb_value alen)
+{
+  mrb_int beg, len;
+
+  switch (str_convert_range(mrb, str, indx, alen, &beg, &len)) {
+    case STR_CHAR_RANGE_CORRECTED:
+      return str_subseq(mrb, str, beg, len);
+    case STR_CHAR_RANGE:
+      str = str_substr(mrb, str, beg, len);
+      if (mrb_undef_p(alen) && !mrb_nil_p(str) && RSTRING_LEN(str) == 0) return mrb_nil_value();
+      return str;
+    case STR_BYTE_RANGE_CORRECTED:
+      if (mrb_string_p(indx)) {
+        return mrb_str_dup(mrb, indx);
+      }
+      else {
+        return mrb_str_byte_subseq(mrb, str, beg, len);
       }
-      idx = mrb_fixnum(indx);
-      goto num_index;
+    case STR_OUT_OF_RANGE:
+    default:
+      return mrb_nil_value();
   }
-  return mrb_nil_value();    /* not reached */
 }
 
 /* 15.2.10.5.6  */
@@ -1131,20 +1208,118 @@ static mrb_value
 mrb_str_aref_m(mrb_state *mrb, mrb_value str)
 {
   mrb_value a1, a2;
-  mrb_int argc;
 
-  argc = mrb_get_args(mrb, "o|o", &a1, &a2);
-  if (argc == 2) {
-    mrb_int n1, n2;
+  if (mrb_get_args(mrb, "o|o", &a1, &a2) == 1) {
+    a2 = mrb_undef_value();
+  }
+
+  return mrb_str_aref(mrb, str, a1, a2);
+}
+
+static mrb_noreturn void
+str_out_of_index(mrb_state *mrb, mrb_value index)
+{
+  mrb_raisef(mrb, E_INDEX_ERROR, "index %S out of string", index);
+}
+
+static mrb_value
+str_replace_partial(mrb_state *mrb, mrb_value src, mrb_int pos, mrb_int end, mrb_value rep)
+{
+  const mrb_int shrink_threshold = 256;
+  struct RString *str = mrb_str_ptr(src);
+  mrb_int len = RSTR_LEN(str);
+  mrb_int replen, newlen;
+  char *strp;
+
+  if (end > len) { end = len; }
+
+  if (pos < 0 || pos > len) {
+    str_out_of_index(mrb, mrb_fixnum_value(pos));
+  }
+
+  replen = (mrb_nil_p(rep) ? 0 : RSTRING_LEN(rep));
+  newlen = replen + len - (end - pos);
 
-    mrb_regexp_check(mrb, a1);
-    mrb_get_args(mrb, "ii", &n1, &n2);
-    return str_substr(mrb, str, n1, n2);
+  if (newlen >= MRB_INT_MAX || newlen < replen /* overflowed */) {
+    mrb_raise(mrb, E_RUNTIME_ERROR, "string size too big");
   }
-  if (argc != 1) {
-    mrb_raisef(mrb, E_ARGUMENT_ERROR, "wrong number of arguments (%S for 1)", mrb_fixnum_value(argc));
+
+  mrb_str_modify(mrb, str);
+
+  if (len < newlen) {
+    resize_capa(mrb, str, newlen);
+  }
+
+  strp = RSTR_PTR(str);
+
+  memmove(strp + newlen - (len - end), strp + end, len - end);
+  if (!mrb_nil_p(rep)) {
+    memcpy(strp + pos, RSTRING_PTR(rep), replen);
+  }
+  RSTR_SET_LEN(str, newlen);
+  strp[newlen] = '\0';
+
+  if (len - newlen >= shrink_threshold) {
+    resize_capa(mrb, str, newlen);
+  }
+
+  return src;
+}
+
+static void
+mrb_str_aset(mrb_state *mrb, mrb_value str, mrb_value indx, mrb_value alen, mrb_value replace)
+{
+  mrb_int beg, len, charlen;
+
+  replace = mrb_to_str(mrb, replace);
+
+  switch (str_convert_range(mrb, str, indx, alen, &beg, &len)) {
+    case STR_OUT_OF_RANGE:
+    default:
+      mrb_raise(mrb, E_INDEX_ERROR, "string not matched");
+    case STR_CHAR_RANGE:
+      if (len < 0) {
+        mrb_raisef(mrb, E_INDEX_ERROR, "negative length %S", alen);
+      }
+      charlen = RSTRING_CHAR_LEN(str);
+      if (beg < 0) { beg += charlen; }
+      if (beg < 0 || beg > charlen) { str_out_of_index(mrb, indx); }
+      /* fall through */
+    case STR_CHAR_RANGE_CORRECTED:
+      str_range_to_bytes(str, &beg, &len);
+      /* fall through */
+    case STR_BYTE_RANGE_CORRECTED:
+      str_replace_partial(mrb, str, beg, beg + len, replace);
+  }
+}
+
+/*
+ * call-seq:
+ *    str[fixnum] = replace
+ *    str[fixnum, fixnum] = replace
+ *    str[range] = replace
+ *    str[regexp] = replace
+ *    str[regexp, fixnum] = replace
+ *    str[other_str] = replace
+ *
+ * Modify +self+ by replacing the content of +self+.
+ * The portion of the string affected is determined using the same criteria as +String#[]+.
+ */
+static mrb_value
+mrb_str_aset_m(mrb_state *mrb, mrb_value str)
+{
+  mrb_value indx, alen, replace;
+
+  switch (mrb_get_args(mrb, "oo|S!", &indx, &alen, &replace)) {
+    case 2:
+      replace = alen;
+      alen = mrb_undef_value();
+      break;
+    case 3:
+      break;
   }
-  return mrb_str_aref(mrb, str, a1);
+  mrb_str_aset(mrb, str, indx, alen, replace);
+  return str;
 }
 
 /* 15.2.10.5.8  */
@@ -1167,7 +1342,7 @@ mrb_str_capitalize_bang(mrb_state *mrb, mrb_value str)
   mrb_bool modify = FALSE;
   struct RString *s = mrb_str_ptr(str);
 
-  mrb_str_modify(mrb, s);
+  mrb_str_modify_keep_ascii(mrb, s);
   if (RSTR_LEN(s) == 0 || !RSTR_PTR(s)) return mrb_nil_value();
   p = RSTR_PTR(s); pend = RSTR_PTR(s) + RSTR_LEN(s);
   if (ISLOWER(*p)) {
@@ -1226,7 +1401,7 @@ mrb_str_chomp_bang(mrb_state *mrb, mrb_value str)
   struct RString *s = mrb_str_ptr(str);
 
   argc = mrb_get_args(mrb, "|S", &rs);
-  mrb_str_modify(mrb, s);
+  mrb_str_modify_keep_ascii(mrb, s);
   len = RSTR_LEN(s);
   if (argc == 0) {
     if (len == 0) return mrb_nil_value();
@@ -1325,7 +1500,7 @@ mrb_str_chop_bang(mrb_state *mrb, mrb_value str)
 {
   struct RString *s = mrb_str_ptr(str);
 
-  mrb_str_modify(mrb, s);
+  mrb_str_modify_keep_ascii(mrb, s);
   if (RSTR_LEN(s) > 0) {
     mrb_int len;
 #ifdef MRB_UTF8_STRING
@@ -1394,7 +1569,7 @@ mrb_str_downcase_bang(mrb_state *mrb, mrb_value str)
   mrb_bool modify = FALSE;
   struct RString *s = mrb_str_ptr(str);
 
-  mrb_str_modify(mrb, s);
+  mrb_str_modify_keep_ascii(mrb, s);
   p = RSTR_PTR(s);
   pend = RSTR_PTR(s) + RSTR_LEN(s);
   while (p < pend) {
@@ -1567,16 +1742,13 @@ mrb_str_index_m(mrb_state *mrb, mrb_value str)
     else
       sub = mrb_nil_value();
   }
-  mrb_regexp_check(mrb, sub);
-  clen = RSTRING_CHAR_LEN(str);
   if (pos < 0) {
+    clen = RSTRING_CHAR_LEN(str);
     pos += clen;
     if (pos < 0) {
       return mrb_nil_value();
     }
   }
-  if (pos > clen) return mrb_nil_value();
-  pos = chars2bytes(str, 0, pos);
 
   switch (mrb_type(sub)) {
     default: {
@@ -1590,18 +1762,15 @@ mrb_str_index_m(mrb_state *mrb, mrb_value str)
     }
     /* fall through */
     case MRB_TT_STRING:
-      pos = str_index_str(mrb, str, sub, pos);
+      pos = str_index_str_by_char(mrb, str, sub, pos);
       break;
   }
 
   if (pos == -1) return mrb_nil_value();
-  pos = bytes2chars(RSTRING_PTR(str), pos);
   BYTES_ALIGN_CHECK(pos);
   return mrb_fixnum_value(pos);
 }
 
-#define STR_REPLACE_SHARED_MIN 10
-
 /* 15.2.10.5.24 */
 /* 15.2.10.5.28 */
 /*
@@ -1711,16 +1880,16 @@ mrb_ptr_to_str(mrb_state *mrb, void *p)
   return mrb_obj_value(p_str);
 }
 
-MRB_API mrb_value
-mrb_string_type(mrb_state *mrb, mrb_value str)
+static inline void
+str_reverse(char *p, char *e)
 {
-  return mrb_convert_type(mrb, str, MRB_TT_STRING, "String", "to_str");
-}
+  char c;
 
-MRB_API mrb_value
-mrb_check_string_type(mrb_state *mrb, mrb_value str)
-{
-  return mrb_check_convert_type(mrb, str, MRB_TT_STRING, "String", "to_str");
+  while (p < e) {
+    c = *p;
+    *p++ = *e;
+    *e-- = c;
+  }
 }
 
 /* 15.2.10.5.30 */
@@ -1733,53 +1902,38 @@ mrb_check_string_type(mrb_state *mrb, mrb_value str)
 static mrb_value
 mrb_str_reverse_bang(mrb_state *mrb, mrb_value str)
 {
+  struct RString *s = mrb_str_ptr(str);
+  char *p, *e;
+
 #ifdef MRB_UTF8_STRING
   mrb_int utf8_len = RSTRING_CHAR_LEN(str);
-  mrb_int len = RSTRING_LEN(str);
-
-  if (utf8_len == len) goto bytes;
-  if (utf8_len > 1) {
-    char *buf;
-    char *p, *e, *r;
-
-    mrb_str_modify(mrb, mrb_str_ptr(str));
-    len = RSTRING_LEN(str);
-    buf = (char*)mrb_malloc(mrb, (size_t)len);
-    p = buf;
-    e = buf + len;
-
-    memcpy(buf, RSTRING_PTR(str), len);
-    r = RSTRING_PTR(str) + len;
+  mrb_int len = RSTR_LEN(s);
 
+  if (utf8_len < 2) return str;
+  if (utf8_len < len) {
+    mrb_str_modify(mrb, s);
+    p = RSTR_PTR(s);
+    e = p + RSTR_LEN(s);
     while (p<e) {
       mrb_int clen = utf8len(p, e);
-      r -= clen;
-      memcpy(r, p, clen);
+      str_reverse(p, p + clen - 1);
       p += clen;
     }
-    mrb_free(mrb, buf);
+    goto bytes;
   }
-  return str;
-
- bytes:
 #endif
-  {
-    struct RString *s = mrb_str_ptr(str);
-    char *p, *e;
-    char c;
 
+  if (RSTR_LEN(s) > 1) {
     mrb_str_modify(mrb, s);
-    if (RSTR_LEN(s) > 1) {
-      p = RSTR_PTR(s);
-      e = p + RSTR_LEN(s) - 1;
-      while (p < e) {
-      c = *p;
-      *p++ = *e;
-      *e-- = c;
-      }
-    }
-    return str;
+    goto bytes;
   }
+  return str;
+
+ bytes:
+  p = RSTR_PTR(s);
+  e = p + RSTR_LEN(s) - 1;
+  str_reverse(p, e);
+  return str;
 }
 
 /* ---------------------------------- */
@@ -1833,7 +1987,6 @@ mrb_str_rindex(mrb_state *mrb, mrb_value str)
     if (pos < 0) {
       pos += len;
       if (pos < 0) {
-        mrb_regexp_check(mrb, sub);
         return mrb_nil_value();
       }
     }
@@ -1847,7 +2000,6 @@ mrb_str_rindex(mrb_state *mrb, mrb_value str)
       sub = mrb_nil_value();
   }
   pos = chars2bytes(str, 0, pos);
-  mrb_regexp_check(mrb, sub);
 
   switch (mrb_type(sub)) {
     default: {
@@ -1941,16 +2093,11 @@ mrb_str_split_m(mrb_state *mrb, mrb_value str)
   if (argc == 0 || mrb_nil_p(spat)) {
     split_type = awk;
   }
-  else {
-    if (mrb_string_p(spat)) {
-      split_type = string;
-      if (RSTRING_LEN(spat) == 1 && RSTRING_PTR(spat)[0] == ' ') {
-          split_type = awk;
-      }
-    }
-    else {
-      mrb_noregexp(mrb, str);
-    }
+  else if (!mrb_string_p(spat)) {
+    mrb_raise(mrb, E_TYPE_ERROR, "expected String");
+  }
+  else if (RSTRING_LEN(spat) == 1 && RSTRING_PTR(spat)[0] == ' ') {
+    split_type = awk;
   }
 
   result = mrb_ary_new(mrb);
@@ -1976,7 +2123,7 @@ mrb_str_split_m(mrb_state *mrb, mrb_value str)
         }
       }
       else if (ISSPACE(c)) {
-        mrb_ary_push(mrb, result, byte_subseq(mrb, str, beg, end-beg));
+        mrb_ary_push(mrb, result, mrb_str_byte_subseq(mrb, str, beg, end-beg));
         mrb_gc_arena_restore(mrb, ai);
         skip = TRUE;
         beg = idx;
@@ -1987,7 +2134,7 @@ mrb_str_split_m(mrb_state *mrb, mrb_value str)
       }
     }
   }
-  else if (split_type == string) {
+  else {                        /* split_type == string */
     mrb_int str_len = RSTRING_LEN(str);
     mrb_int pat_len = RSTRING_LEN(spat);
     mrb_int idx = 0;
@@ -2001,22 +2148,19 @@ mrb_str_split_m(mrb_state *mrb, mrb_value str)
       else {
         end = chars2bytes(str, idx, 1);
       }
-      mrb_ary_push(mrb, result, byte_subseq(mrb, str, idx, end));
+      mrb_ary_push(mrb, result, mrb_str_byte_subseq(mrb, str, idx, end));
       mrb_gc_arena_restore(mrb, ai);
       idx += end + pat_len;
       if (lim_p && lim <= ++i) break;
     }
     beg = idx;
   }
-  else {
-    mrb_noregexp(mrb, str);
-  }
   if (RSTRING_LEN(str) > 0 && (lim_p || RSTRING_LEN(str) > beg || lim < 0)) {
     if (RSTRING_LEN(str) == beg) {
       tmp = mrb_str_new_empty(mrb, str);
     }
     else {
-      tmp = byte_subseq(mrb, str, beg, RSTRING_LEN(str)-beg);
+      tmp = mrb_str_byte_subseq(mrb, str, beg, RSTRING_LEN(str)-beg);
     }
     mrb_ary_push(mrb, result, tmp);
   }
@@ -2030,7 +2174,7 @@ mrb_str_split_m(mrb_state *mrb, mrb_value str)
   return result;
 }
 
-MRB_API mrb_value
+static mrb_value
 mrb_str_len_to_inum(mrb_state *mrb, const char *str, mrb_int len, mrb_int base, int badcheck)
 {
   const char *p = str;
@@ -2174,7 +2318,7 @@ mrb_str_len_to_inum(mrb_state *mrb, const char *str, mrb_int len, mrb_int base,
       else
 #endif
       {
-        mrb_raisef(mrb, E_ARGUMENT_ERROR, "string (%S) too big for integer",
+        mrb_raisef(mrb, E_RANGE_ERROR, "string (%S) too big for integer",
                    mrb_str_new(mrb, str, pend-str));
       }
     }
@@ -2198,7 +2342,7 @@ mrb_str_len_to_inum(mrb_state *mrb, const char *str, mrb_int len, mrb_int base,
 }
 
 MRB_API mrb_value
-mrb_cstr_to_inum(mrb_state *mrb, const char *str, int base, int badcheck)
+mrb_cstr_to_inum(mrb_state *mrb, const char *str, mrb_int base, mrb_bool badcheck)
 {
   return mrb_str_len_to_inum(mrb, str, strlen(str), base, badcheck);
 }
@@ -2206,20 +2350,27 @@ mrb_cstr_to_inum(mrb_state *mrb, const char *str, int base, int badcheck)
 MRB_API const char*
 mrb_string_value_cstr(mrb_state *mrb, mrb_value *ptr)
 {
-  mrb_value str = mrb_str_to_str(mrb, *ptr);
-  struct RString *ps = mrb_str_ptr(str);
-  mrb_int len = mrb_str_strlen(mrb, ps);
-  char *p = RSTR_PTR(ps);
+  struct RString *ps;
+  const char *p;
+  mrb_int len;
 
-  if (!p || p[len] != '\0') {
+  check_null_byte(mrb, *ptr);
+  ps = mrb_str_ptr(*ptr);
+  p = RSTR_PTR(ps);
+  len = RSTR_LEN(ps);
+  if (p[len] == '\0') {
+    return p;
+  }
+  else {
     if (MRB_FROZEN_P(ps)) {
-      *ptr = str = mrb_str_dup(mrb, str);
-      ps = mrb_str_ptr(str);
+      ps = str_new(mrb, p, len);
+      *ptr = mrb_obj_value(ps);
+    }
+    else {
+      mrb_str_modify(mrb, ps);
     }
-    mrb_str_modify(mrb, ps);
     return RSTR_PTR(ps);
   }
-  return p;
 }
 
 MRB_API mrb_value
@@ -2333,22 +2484,7 @@ bad:
 MRB_API double
 mrb_str_to_dbl(mrb_state *mrb, mrb_value str, mrb_bool badcheck)
 {
-  char *s;
-  mrb_int len;
-
-  str = mrb_str_to_str(mrb, str);
-  s = RSTRING_PTR(str);
-  len = RSTRING_LEN(str);
-  if (s) {
-    if (badcheck && memchr(s, '\0', len)) {
-      mrb_raise(mrb, E_ARGUMENT_ERROR, "string for Float contains null byte");
-    }
-    if (s[len]) {    /* no sentinel somehow */
-      struct RString *temp_str = str_new(mrb, s, len);
-      s = RSTR_PTR(temp_str);
-    }
-  }
-  return mrb_cstr_to_dbl(mrb, s, badcheck);
+  return mrb_cstr_to_dbl(mrb, mrb_string_value_cstr(mrb, &str), badcheck);
 }
 
 /* 15.2.10.5.39 */
@@ -2376,7 +2512,6 @@ mrb_str_to_f(mrb_state *mrb, mrb_value self)
 /*
  *  call-seq:
  *     str.to_s     => str
- *     str.to_str   => str
  *
  *  Returns the receiver.
  */
@@ -2404,7 +2539,7 @@ mrb_str_upcase_bang(mrb_state *mrb, mrb_value str)
   char *p, *pend;
   mrb_bool modify = FALSE;
 
-  mrb_str_modify(mrb, s);
+  mrb_str_modify_keep_ascii(mrb, s);
   p = RSTRING_PTR(str);
   pend = RSTRING_END(str);
   while (p < pend) {
@@ -2485,7 +2620,7 @@ mrb_str_dump(mrb_state *mrb, mrb_value str)
   }
 
   result = str_new(mrb, 0, len);
-  str_with_class(mrb, result, str);
+  str_with_class(result, str);
   p = RSTRING_PTR(str); pend = p + RSTRING_LEN(str);
   q = RSTR_PTR(result);
   *q++ = '"';
@@ -2624,7 +2759,7 @@ mrb_str_cat_str(mrb_state *mrb, mrb_value str, mrb_value str2)
 MRB_API mrb_value
 mrb_str_append(mrb_state *mrb, mrb_value str1, mrb_value str2)
 {
-  str2 = mrb_str_to_str(mrb, str2);
+  mrb_to_str(mrb, str2);
   return mrb_str_cat_str(mrb, str1, str2);
 }
 
@@ -2704,6 +2839,7 @@ mrb_str_inspect(mrb_state *mrb, mrb_value str)
     }
   }
   mrb_str_cat_lit(mrb, result, "\"");
+  RSTR_COPY_ASCII_FLAG(mrb_str_ptr(result), mrb_str_ptr(str));
 
   return result;
 }
@@ -2749,6 +2885,7 @@ mrb_init_string(mrb_state *mrb)
   mrb_define_method(mrb, s, "+",               mrb_str_plus_m,          MRB_ARGS_REQ(1)); /* 15.2.10.5.4  */
   mrb_define_method(mrb, s, "*",               mrb_str_times,           MRB_ARGS_REQ(1)); /* 15.2.10.5.5  */
   mrb_define_method(mrb, s, "[]",              mrb_str_aref_m,          MRB_ARGS_ANY());  /* 15.2.10.5.6  */
+  mrb_define_method(mrb, s, "[]=",             mrb_str_aset_m,          MRB_ARGS_ANY());
   mrb_define_method(mrb, s, "capitalize",      mrb_str_capitalize,      MRB_ARGS_NONE()); /* 15.2.10.5.7  */
   mrb_define_method(mrb, s, "capitalize!",     mrb_str_capitalize_bang, MRB_ARGS_NONE()); /* 15.2.10.5.8  */
   mrb_define_method(mrb, s, "chomp",           mrb_str_chomp,           MRB_ARGS_ANY());  /* 15.2.10.5.9  */
@@ -2869,7 +3006,7 @@ mrb_float_read(const char *string, char **endPtr)
      */
 
     p = string;
-    while (isspace(*p)) {
+    while (ISSPACE(*p)) {
       p += 1;
     }
     if (*p == '-') {
@@ -2892,7 +3029,7 @@ mrb_float_read(const char *string, char **endPtr)
     for (mantSize = 0; ; mantSize += 1)
     {
       c = *p;
-      if (!isdigit(c)) {
+      if (!ISDIGIT(c)) {
         if ((c != '.') || (decPt >= 0)) {
           break;
         }
@@ -2977,7 +3114,7 @@ mrb_float_read(const char *string, char **endPtr)
         }
         expSign = FALSE;
       }
-      while (isdigit(*p)) {
+      while (ISDIGIT(*p)) {
         exp = exp * 10 + (*p - '0');
         if (exp > 19999) {
           exp = 19999;
diff --git a/src/symbol.c b/src/symbol.c
index 5e1f9f561..53f4f6e1d 100644
--- a/src/symbol.c
+++ b/src/symbol.c
@@ -15,54 +15,158 @@
 /* ------------------------------------------------------ */
 typedef struct symbol_name {
   mrb_bool lit : 1;
+  uint8_t prev;
   uint16_t len;
   const char *name;
 } symbol_name;
 
-static inline khint_t
-sym_hash_func(mrb_state *mrb, mrb_sym s)
+#define SYMBOL_INLINE_BIT       1
+#define SYMBOL_INLINE_LOWER_BIT 2
+#define SYMBOL_INLINE           (1 << (SYMBOL_INLINE_BIT - 1))
+#define SYMBOL_INLINE_LOWER     (1 << (SYMBOL_INLINE_LOWER_BIT - 1))
+#define SYMBOL_NORMAL_SHIFT     SYMBOL_INLINE_BIT
+#define SYMBOL_INLINE_SHIFT     SYMBOL_INLINE_LOWER_BIT
+#ifdef MRB_ENABLE_ALL_SYMBOLS
+# define SYMBOL_INLINE_P(sym) FALSE
+# define SYMBOL_INLINE_LOWER_P(sym) FALSE
+# define sym_inline_pack(name, len) 0
+# define sym_inline_unpack(sym, buf, lenp) NULL
+#else
+# define SYMBOL_INLINE_P(sym) ((sym) & SYMBOL_INLINE)
+# define SYMBOL_INLINE_LOWER_P(sym) ((sym) & SYMBOL_INLINE_LOWER)
+#endif
+
+static void
+sym_validate_len(mrb_state *mrb, size_t len)
 {
-  khint_t h = 0;
-  size_t i, len = mrb->symtbl[s].len;
-  const char *p = mrb->symtbl[s].name;
+  if (len >= RITE_LV_NULL_MARK) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "symbol length too long");
+  }
+}
 
+#ifndef MRB_ENABLE_ALL_SYMBOLS
+static const char pack_table[] = "_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
+
+static mrb_sym
+sym_inline_pack(const char *name, uint16_t len)
+{
+  const int lower_length_max = (MRB_SYMBOL_BITSIZE - 2) / 5;
+  const int mix_length_max   = (MRB_SYMBOL_BITSIZE - 2) / 6;
+
+  char c;
+  const char *p;
+  int i;
+  mrb_sym sym = 0;
+  mrb_bool lower = TRUE;
+
+  if (len > lower_length_max) return 0; /* too long */
   for (i=0; i<len; i++) {
-    h = (h << 5) - h + *p++;
+    uint32_t bits;
+
+    c = name[i];
+    if (c == 0) return 0;       /* NUL in name */
+    p = strchr(pack_table, (int)c);
+    if (p == 0) return 0;       /* non alnum char */
+    bits = (uint32_t)(p - pack_table)+1;
+    if (bits > 27) lower = FALSE;
+    if (i >= mix_length_max) break;
+    sym |= bits<<(i*6+SYMBOL_INLINE_SHIFT);
   }
-  return h;
+  if (lower) {
+    sym = 0;
+    for (i=0; i<len; i++) {
+      uint32_t bits;
+
+      c = name[i];
+      p = strchr(pack_table, (int)c);
+      bits = (uint32_t)(p - pack_table)+1;
+      sym |= bits<<(i*5+SYMBOL_INLINE_SHIFT);
+    }
+    return sym | SYMBOL_INLINE | SYMBOL_INLINE_LOWER;
+  }
+  if (len > mix_length_max) return 0;
+  return sym | SYMBOL_INLINE;
 }
-#define sym_hash_equal(mrb,a, b) (mrb->symtbl[a].len == mrb->symtbl[b].len && memcmp(mrb->symtbl[a].name, mrb->symtbl[b].name, mrb->symtbl[a].len) == 0)
-
-KHASH_DECLARE(n2s, mrb_sym, mrb_sym, FALSE)
-KHASH_DEFINE (n2s, mrb_sym, mrb_sym, FALSE, sym_hash_func, sym_hash_equal)
-/* ------------------------------------------------------ */
 
-static void
-sym_validate_len(mrb_state *mrb, size_t len)
+static const char*
+sym_inline_unpack(mrb_sym sym, char *buf, mrb_int *lenp)
 {
-  if (len >= RITE_LV_NULL_MARK) {
-    mrb_raise(mrb, E_ARGUMENT_ERROR, "symbol length too long");
+  int bit_per_char = SYMBOL_INLINE_LOWER_P(sym) ? 5 : 6;
+  int i;
+
+  mrb_assert(SYMBOL_INLINE_P(sym));
+
+  for (i=0; i<30/bit_per_char; i++) {
+    uint32_t bits = sym>>(i*bit_per_char+SYMBOL_INLINE_SHIFT) & ((1<<bit_per_char)-1);
+    if (bits == 0) break;
+    buf[i] = pack_table[bits-1];;
   }
+  buf[i] = '\0';
+  if (lenp) *lenp = i;
+  return buf;
+}
+#endif
+
+static uint8_t
+symhash(const char *key, size_t len)
+{
+    uint32_t hash, i;
+
+    for(hash = i = 0; i < len; ++i) {
+        hash += key[i];
+        hash += (hash << 10);
+        hash ^= (hash >> 6);
+    }
+    hash += (hash << 3);
+    hash ^= (hash >> 11);
+    hash += (hash << 15);
+    return hash & 0xff;
+}
+
+static mrb_sym
+find_symbol(mrb_state *mrb, const char *name, uint16_t len, uint8_t hash)
+{
+  mrb_sym i;
+  symbol_name *sname;
+
+  /* inline symbol */
+  i = sym_inline_pack(name, len);
+  if (i > 0) return i;
+
+  i = mrb->symhash[hash];
+  if (i == 0) return 0;
+  do {
+    sname = &mrb->symtbl[i];
+    if (sname->len == len && memcmp(sname->name, name, len) == 0) {
+      return i<<SYMBOL_NORMAL_SHIFT;
+    }
+    if (sname->prev == 0xff) {
+      i -= 0xff;
+      sname = &mrb->symtbl[i];
+      while (mrb->symtbl < sname) {
+        if (sname->len == len && memcmp(sname->name, name, len) == 0) {
+          return (mrb_sym)(sname - mrb->symtbl)<<SYMBOL_NORMAL_SHIFT;
+        }
+        sname--;
+      }
+      return 0;
+    }
+    i -= sname->prev;
+  } while (sname->prev > 0);
+  return 0;
 }
 
 static mrb_sym
 sym_intern(mrb_state *mrb, const char *name, size_t len, mrb_bool lit)
 {
-  khash_t(n2s) *h = mrb->name2sym;
-  symbol_name *sname = mrb->symtbl; /* symtbl[0] for working memory */
-  khiter_t k;
   mrb_sym sym;
-  char *p;
+  symbol_name *sname;
+  uint8_t hash;
 
   sym_validate_len(mrb, len);
-  if (sname) {
-    sname->lit = lit;
-    sname->len = (uint16_t)len;
-    sname->name = name;
-    k = kh_get(n2s, mrb, h, 0);
-    if (k != kh_end(h))
-      return kh_key(h, k);
-  }
+  hash = symhash(name, len);
+  sym = find_symbol(mrb, name, len, hash);
+  if (sym > 0) return sym;
 
   /* registering a new symbol */
   sym = ++mrb->symidx;
@@ -78,15 +182,25 @@ sym_intern(mrb_state *mrb, const char *name, size_t len, mrb_bool lit)
     sname->lit = TRUE;
   }
   else {
-    p = (char *)mrb_malloc(mrb, len+1);
+    char *p = (char *)mrb_malloc(mrb, len+1);
     memcpy(p, name, len);
     p[len] = 0;
     sname->name = (const char*)p;
     sname->lit = FALSE;
   }
-  kh_put(n2s, mrb, h, sym);
+  if (mrb->symhash[hash]) {
+    mrb_sym i = sym - mrb->symhash[hash];
+    if (i > 0xff)
+      sname->prev = 0xff;
+    else
+      sname->prev = i;
+  }
+  else {
+    sname->prev = 0;
+  }
+  mrb->symhash[hash] = sym;
 
-  return sym;
+  return sym<<SYMBOL_NORMAL_SHIFT;
 }
 
 MRB_API mrb_sym
@@ -116,25 +230,18 @@ mrb_intern_str(mrb_state *mrb, mrb_value str)
 MRB_API mrb_value
 mrb_check_intern(mrb_state *mrb, const char *name, size_t len)
 {
-  khash_t(n2s) *h = mrb->name2sym;
-  symbol_name *sname = mrb->symtbl;
-  khiter_t k;
+  mrb_sym sym;
 
   sym_validate_len(mrb, len);
-  sname->len = (uint16_t)len;
-  sname->name = name;
-
-  k = kh_get(n2s, mrb, h, 0);
-  if (k != kh_end(h)) {
-    return mrb_symbol_value(kh_key(h, k));
-  }
+  sym = find_symbol(mrb, name, len, symhash(name, len));
+  if (sym > 0) return mrb_symbol_value(sym);
   return mrb_nil_value();
 }
 
 MRB_API mrb_value
 mrb_check_intern_cstr(mrb_state *mrb, const char *name)
 {
-  return mrb_check_intern(mrb, name, (mrb_int)strlen(name));
+  return mrb_check_intern(mrb, name, strlen(name));
 }
 
 MRB_API mrb_value
@@ -143,10 +250,12 @@ mrb_check_intern_str(mrb_state *mrb, mrb_value str)
   return mrb_check_intern(mrb, RSTRING_PTR(str), RSTRING_LEN(str));
 }
 
-/* lenp must be a pointer to a size_t variable */
-MRB_API const char*
-mrb_sym2name_len(mrb_state *mrb, mrb_sym sym, mrb_int *lenp)
+static const char*
+sym2name_len(mrb_state *mrb, mrb_sym sym, char *buf, mrb_int *lenp)
 {
+  if (SYMBOL_INLINE_P(sym)) return sym_inline_unpack(sym, buf, lenp);
+
+  sym >>= SYMBOL_NORMAL_SHIFT;
   if (sym == 0 || mrb->symidx < sym) {
     if (lenp) *lenp = 0;
     return NULL;
@@ -156,6 +265,12 @@ mrb_sym2name_len(mrb_state *mrb, mrb_sym sym, mrb_int *lenp)
   return mrb->symtbl[sym].name;
 }
 
+MRB_API const char*
+mrb_sym2name_len(mrb_state *mrb, mrb_sym sym, mrb_int *lenp)
+{
+  return sym2name_len(mrb, sym, mrb->symbuf, lenp);
+}
+
 void
 mrb_free_symtbl(mrb_state *mrb)
 {
@@ -167,13 +282,11 @@ mrb_free_symtbl(mrb_state *mrb)
     }
   }
   mrb_free(mrb, mrb->symtbl);
-  kh_destroy(n2s, mrb, mrb->name2sym);
 }
 
 void
 mrb_init_symtbl(mrb_state *mrb)
 {
-  mrb->name2sym = kh_init(n2s, mrb);
 }
 
 /**********************************************************************
@@ -209,26 +322,6 @@ mrb_init_symtbl(mrb_state *mrb)
  *
  */
 
-
-/* 15.2.11.3.1  */
-/*
- *  call-seq:
- *     sym == obj   -> true or false
- *
- *  Equality---If <i>sym</i> and <i>obj</i> are exactly the same
- *  symbol, returns <code>true</code>.
- */
-
-static mrb_value
-sym_equal(mrb_state *mrb, mrb_value sym1)
-{
-  mrb_value sym2;
-
-  mrb_get_args(mrb, "o", &sym2);
-
-  return mrb_bool_value(mrb_obj_equal(mrb, sym1, sym2));
-}
-
 /* 15.2.11.3.2  */
 /* 15.2.11.3.3  */
 /*
@@ -241,14 +334,9 @@ sym_equal(mrb_state *mrb, mrb_value sym1)
  *     :fred.id2name   #=> "fred"
  */
 static mrb_value
-mrb_sym_to_s(mrb_state *mrb, mrb_value sym)
+sym_to_s(mrb_state *mrb, mrb_value sym)
 {
-  mrb_sym id = mrb_symbol(sym);
-  const char *p;
-  mrb_int len;
-
-  p = mrb_sym2name_len(mrb, id, &len);
-  return mrb_str_new_static(mrb, p, len);
+  return mrb_sym2str(mrb, mrb_symbol(sym));
 }
 
 /* 15.2.11.3.4  */
@@ -387,8 +475,8 @@ id:
         switch (*m) {
           case '!': case '?': case '=': ++m;
           default: break;
-            }
         }
+      }
       break;
   }
   return *m ? FALSE : TRUE;
@@ -406,7 +494,7 @@ sym_inspect(mrb_state *mrb, mrb_value sym)
   name = mrb_sym2name_len(mrb, id, &len);
   str = mrb_str_new(mrb, 0, len+1);
   sp = RSTRING_PTR(str);
-  RSTRING_PTR(str)[0] = ':';
+  sp[0] = ':';
   memcpy(sp+1, name, len);
   mrb_assert_int_fit(mrb_int, len, size_t, SIZE_MAX);
   if (!symname_p(name) || strlen(name) != (size_t)len) {
@@ -415,6 +503,9 @@ sym_inspect(mrb_state *mrb, mrb_value sym)
     sp[0] = ':';
     sp[1] = '"';
   }
+#ifdef MRB_UTF8_STRING
+  if (SYMBOL_INLINE_P(id)) RSTR_SET_ASCII_FLAG(mrb_str_ptr(str));
+#endif
   return str;
 }
 
@@ -425,6 +516,11 @@ mrb_sym2str(mrb_state *mrb, mrb_sym sym)
   const char *name = mrb_sym2name_len(mrb, sym, &len);
 
   if (!name) return mrb_undef_value(); /* can't happen */
+  if (SYMBOL_INLINE_P(sym)) {
+    mrb_value str = mrb_str_new(mrb, name, len);
+    RSTR_SET_ASCII_FLAG(mrb_str_ptr(str));
+    return str;
+  }
   return mrb_str_new_static(mrb, name, len);
 }
 
@@ -439,7 +535,9 @@ mrb_sym2name(mrb_state *mrb, mrb_sym sym)
     return name;
   }
   else {
-    mrb_value str = mrb_str_dump(mrb, mrb_str_new_static(mrb, name, len));
+    mrb_value str = SYMBOL_INLINE_P(sym) ?
+      mrb_str_new(mrb, name, len) : mrb_str_new_static(mrb, name, len);
+    str = mrb_str_dump(mrb, str);
     return RSTRING_PTR(str);
   }
 }
@@ -461,9 +559,10 @@ sym_cmp(mrb_state *mrb, mrb_value s1)
     const char *p1, *p2;
     int retval;
     mrb_int len, len1, len2;
+    char buf1[8], buf2[8];
 
-    p1 = mrb_sym2name_len(mrb, sym1, &len1);
-    p2 = mrb_sym2name_len(mrb, sym2, &len2);
+    p1 = sym2name_len(mrb, sym1, buf1, &len1);
+    p2 = sym2name_len(mrb, sym2, buf2, &len2);
     len = lesser(len1, len2);
     retval = memcmp(p1, p2, len);
     if (retval == 0) {
@@ -481,14 +580,13 @@ mrb_init_symbol(mrb_state *mrb)
 {
   struct RClass *sym;
 
-  mrb->symbol_class = sym = mrb_define_class(mrb, "Symbol", mrb->object_class);                 /* 15.2.11 */
+  mrb->symbol_class = sym = mrb_define_class(mrb, "Symbol", mrb->object_class);  /* 15.2.11 */
   MRB_SET_INSTANCE_TT(sym, MRB_TT_SYMBOL);
   mrb_undef_class_method(mrb,  sym, "new");
 
-  mrb_define_method(mrb, sym, "===",             sym_equal,      MRB_ARGS_REQ(1));              /* 15.2.11.3.1  */
-  mrb_define_method(mrb, sym, "id2name",         mrb_sym_to_s,   MRB_ARGS_NONE());              /* 15.2.11.3.2  */
-  mrb_define_method(mrb, sym, "to_s",            mrb_sym_to_s,   MRB_ARGS_NONE());              /* 15.2.11.3.3  */
-  mrb_define_method(mrb, sym, "to_sym",          sym_to_sym,     MRB_ARGS_NONE());              /* 15.2.11.3.4  */
-  mrb_define_method(mrb, sym, "inspect",         sym_inspect,    MRB_ARGS_NONE());              /* 15.2.11.3.5(x)  */
-  mrb_define_method(mrb, sym, "<=>",             sym_cmp,        MRB_ARGS_REQ(1));
+  mrb_define_method(mrb, sym, "id2name", sym_to_s,    MRB_ARGS_NONE());          /* 15.2.11.3.2 */
+  mrb_define_method(mrb, sym, "to_s",    sym_to_s,    MRB_ARGS_NONE());          /* 15.2.11.3.3 */
+  mrb_define_method(mrb, sym, "to_sym",  sym_to_sym,  MRB_ARGS_NONE());          /* 15.2.11.3.4 */
+  mrb_define_method(mrb, sym, "inspect", sym_inspect, MRB_ARGS_NONE());          /* 15.2.11.3.5(x) */
+  mrb_define_method(mrb, sym, "<=>",     sym_cmp,     MRB_ARGS_REQ(1));
 }
diff --git a/src/variable.c b/src/variable.c
index de36efac6..e6f2f397e 100644
--- a/src/variable.c
+++ b/src/variable.c
@@ -9,155 +9,241 @@
 #include <mruby/class.h>
 #include <mruby/proc.h>
 #include <mruby/string.h>
+#include <mruby/variable.h>
 
-typedef int (iv_foreach_func)(mrb_state*,mrb_sym,mrb_value,void*);
-
-#include <mruby/khash.h>
-
-#ifndef MRB_IVHASH_INIT_SIZE
-#define MRB_IVHASH_INIT_SIZE KHASH_MIN_SIZE
+#ifndef MRB_IV_SEGMENT_SIZE
+#define MRB_IV_SEGMENT_SIZE 4
 #endif
 
-KHASH_DECLARE(iv, mrb_sym, mrb_value, TRUE)
-KHASH_DEFINE(iv, mrb_sym, mrb_value, TRUE, kh_int_hash_func, kh_int_hash_equal)
+typedef struct segment {
+  mrb_sym key[MRB_IV_SEGMENT_SIZE];
+  mrb_value val[MRB_IV_SEGMENT_SIZE];
+  struct segment *next;
+} segment;
 
 /* Instance variable table structure */
 typedef struct iv_tbl {
-  khash_t(iv) h;
+  segment *rootseg;
+  size_t size;
+  size_t last_len;
 } iv_tbl;
 
-/*
- * Creates the instance variable table.
- *
- * Parameters
- *   mrb
- * Returns
- *   the instance variable table.
- */
+/* Creates the instance variable table. */
 static iv_tbl*
 iv_new(mrb_state *mrb)
 {
-  return (iv_tbl*)kh_init_size(iv, mrb, MRB_IVHASH_INIT_SIZE);
+  iv_tbl *t;
+
+  t = (iv_tbl*)mrb_malloc(mrb, sizeof(iv_tbl));
+  t->size = 0;
+  t->rootseg =  NULL;
+  t->last_len = 0;
+
+  return t;
 }
 
-/*
- * Set the value for the symbol in the instance variable table.
- *
- * Parameters
- *   mrb
- *   t     the instance variable table to be set in.
- *   sym   the symbol to be used as the key.
- *   val   the value to be set.
- */
+/* Set the value for the symbol in the instance variable table. */
 static void
 iv_put(mrb_state *mrb, iv_tbl *t, mrb_sym sym, mrb_value val)
 {
-  khash_t(iv) *h = &t->h;
-  khiter_t k;
+  segment *seg;
+  segment *prev = NULL;
+  segment *matched_seg = NULL;
+  size_t matched_idx = 0;
+  size_t i;
+
+  if (t == NULL) return;
+  seg = t->rootseg;
+  while (seg) {
+    for (i=0; i<MRB_IV_SEGMENT_SIZE; i++) {
+      mrb_sym key = seg->key[i];
+      /* Found room in last segment after last_len */
+      if (!seg->next && i >= t->last_len) {
+        seg->key[i] = sym;
+        seg->val[i] = val;
+        t->last_len = i+1;
+        t->size++;
+        return;
+      }
+      if (!matched_seg && key == 0) {
+        matched_seg = seg;
+        matched_idx = i;
+      }
+      else if (key == sym) {
+        seg->val[i] = val;
+        return;
+      }
+    }
+    prev = seg;
+    seg = seg->next;
+  }
 
-  k = kh_put(iv, mrb, h, sym);
-  kh_value(h, k) = val;
+  /* Not found */
+  if (matched_seg) {
+    matched_seg->key[matched_idx] = sym;
+    matched_seg->val[matched_idx] = val;
+    t->size++;
+    return;
+  }
+
+  seg = (segment*)mrb_malloc(mrb, sizeof(segment));
+  seg->next = NULL;
+  seg->key[0] = sym;
+  seg->val[0] = val;
+  t->last_len = 1;
+  t->size++;
+  if (prev) {
+    prev->next = seg;
+  }
+  else {
+    t->rootseg = seg;
+  }
 }
 
-/*
- * Get a value for a symbol from the instance variable table.
- *
- * Parameters
- *   mrb
- *   t     the variable table to be searched.
- *   sym   the symbol to be used as the key.
- *   vp    the value pointer. Receives the value if the specified symbol is
- *         contained in the instance variable table.
- * Returns
- *   true if the specified symbol is contained in the instance variable table.
- */
+/* Get a value for a symbol from the instance variable table. */
 static mrb_bool
 iv_get(mrb_state *mrb, iv_tbl *t, mrb_sym sym, mrb_value *vp)
 {
-  khash_t(iv) *h = &t->h;
-  khiter_t k;
+  segment *seg;
+  size_t i;
 
-  k = kh_get(iv, mrb, h, sym);
-  if (k != kh_end(h)) {
-    if (vp) *vp = kh_value(h, k);
-    return TRUE;
+  if (t == NULL) return FALSE;
+  seg = t->rootseg;
+  while (seg) {
+    for (i=0; i<MRB_IV_SEGMENT_SIZE; i++) {
+      mrb_sym key = seg->key[i];
+
+      if (!seg->next && i >= t->last_len) {
+        return FALSE;
+      }
+      if (key == sym) {
+        if (vp) *vp = seg->val[i];
+        return TRUE;
+      }
+    }
+    seg = seg->next;
   }
   return FALSE;
 }
 
-/*
- * Deletes the value for the symbol from the instance variable table.
- *
- * Parameters
- *   t    the variable table to be searched.
- *   sym  the symbol to be used as the key.
- *   vp   the value pointer. Receive the deleted value if the symbol is
- *        contained in the instance variable table.
- * Returns
- *   true if the specified symbol is contained in the instance variable table.
- */
+/* Deletes the value for the symbol from the instance variable table. */
 static mrb_bool
 iv_del(mrb_state *mrb, iv_tbl *t, mrb_sym sym, mrb_value *vp)
 {
+  segment *seg;
+  size_t i;
+
   if (t == NULL) return FALSE;
-  else {
-    khash_t(iv) *h = &t->h;
-    khiter_t k;
-
-    k = kh_get(iv, mrb, h, sym);
-    if (k != kh_end(h)) {
-      mrb_value val = kh_value(h, k);
-      kh_del(iv, mrb, h, k);
-      if (vp) *vp = val;
-      return TRUE;
+  seg = t->rootseg;
+  while (seg) {
+    for (i=0; i<MRB_IV_SEGMENT_SIZE; i++) {
+      mrb_sym key = seg->key[i];
+
+      if (!seg->next && i >= t->last_len) {
+        return FALSE;
+      }
+      if (key == sym) {
+        t->size--;
+        seg->key[i] = 0;
+        if (vp) *vp = seg->val[i];
+        return TRUE;
+      }
     }
+    seg = seg->next;
   }
   return FALSE;
 }
 
-static mrb_bool
-iv_foreach(mrb_state *mrb, iv_tbl *t, iv_foreach_func *func, void *p)
+/* Iterates over the instance variable table. */
+static void
+iv_foreach(mrb_state *mrb, iv_tbl *t, mrb_iv_foreach_func *func, void *p)
 {
-  if (t == NULL) {
-    return TRUE;
-  }
-  else {
-    khash_t(iv) *h = &t->h;
-    khiter_t k;
-    int n;
-
-    for (k = kh_begin(h); k != kh_end(h); k++) {
-      if (kh_exist(h, k)) {
-        n = (*func)(mrb, kh_key(h, k), kh_value(h, k), p);
-        if (n > 0) return FALSE;
-        if (n < 0) {
-          kh_del(iv, mrb, h, k);
+  segment *seg;
+  size_t i;
+
+  if (t == NULL) return;
+  seg = t->rootseg;
+  while (seg) {
+    for (i=0; i<MRB_IV_SEGMENT_SIZE; i++) {
+      mrb_sym key = seg->key[i];
+
+      /* no value in last segment after last_len */
+      if (!seg->next && i >= t->last_len) {
+        return;
+      }
+      if (key != 0) {
+        if ((*func)(mrb, key, seg->val[i], p) != 0) {
+          return;
         }
       }
     }
+    seg = seg->next;
   }
-  return TRUE;
+  return;
 }
 
+/* Get the size of the instance variable table. */
 static size_t
 iv_size(mrb_state *mrb, iv_tbl *t)
 {
-  if (t) {
-    return kh_size(&t->h);
+  segment *seg;
+  size_t size = 0;
+
+  if (t == NULL) return 0;
+  if (t->size > 0) return t->size;
+  seg = t->rootseg;
+  while (seg) {
+    if (seg->next == NULL) {
+      size += t->last_len;
+      return size;
+    }
+    seg = seg->next;
+    size += MRB_IV_SEGMENT_SIZE;
   }
+  /* empty iv_tbl */
   return 0;
 }
 
+/* Copy the instance variable table. */
 static iv_tbl*
 iv_copy(mrb_state *mrb, iv_tbl *t)
 {
-  return (iv_tbl*)kh_copy(iv, mrb, &t->h);
+  segment *seg;
+  iv_tbl *t2;
+
+  size_t i;
+
+  seg = t->rootseg;
+  t2 = iv_new(mrb);
+
+  while (seg != NULL) {
+    for (i=0; i<MRB_IV_SEGMENT_SIZE; i++) {
+      mrb_sym key = seg->key[i];
+      mrb_value val = seg->val[i];
+
+      if ((seg->next == NULL) && (i >= t->last_len)) {
+        return t2;
+      }
+      iv_put(mrb, t2, key, val);
+    }
+    seg = seg->next;
+  }
+  return t2;
 }
 
+/* Free memory of the instance variable table. */
 static void
 iv_free(mrb_state *mrb, iv_tbl *t)
 {
-  kh_destroy(iv, mrb, &t->h);
+  segment *seg;
+
+  seg = t->rootseg;
+  while (seg) {
+    segment *p = seg;
+    seg = seg->next;
+    mrb_free(mrb, p);
+  }
+  mrb_free(mrb, t);
 }
 
 static int
@@ -170,9 +256,7 @@ iv_mark_i(mrb_state *mrb, mrb_sym sym, mrb_value v, void *p)
 static void
 mark_tbl(mrb_state *mrb, iv_tbl *t)
 {
-  if (t) {
-    iv_foreach(mrb, t, iv_mark_i, 0);
-  }
+  iv_foreach(mrb, t, iv_mark_i, 0);
 }
 
 void
@@ -255,19 +339,64 @@ mrb_iv_get(mrb_state *mrb, mrb_value obj, mrb_sym sym)
   return mrb_nil_value();
 }
 
+static inline void assign_class_name(mrb_state *mrb, struct RObject *obj, mrb_sym sym, mrb_value v);
+
+void
+mrb_obj_iv_set_force(mrb_state *mrb, struct RObject *obj, mrb_sym sym, mrb_value v)
+{
+  assign_class_name(mrb, obj, sym, v);
+  if (!obj->iv) {
+    obj->iv = iv_new(mrb);
+  }
+  iv_put(mrb, obj->iv, sym, v);
+  mrb_write_barrier(mrb, (struct RBasic*)obj);
+}
+
 MRB_API void
 mrb_obj_iv_set(mrb_state *mrb, struct RObject *obj, mrb_sym sym, mrb_value v)
 {
-  iv_tbl *t = obj->iv;
+  mrb_check_frozen(mrb, obj);
+  mrb_obj_iv_set_force(mrb, obj, sym, v);
+}
 
-  if (MRB_FROZEN_P(obj)) {
-    mrb_raisef(mrb, E_FROZEN_ERROR, "can't modify frozen %S", mrb_obj_value(obj));
-  }
-  if (!t) {
-    t = obj->iv = iv_new(mrb);
+/* Iterates over the instance variable table. */
+MRB_API void
+mrb_iv_foreach(mrb_state *mrb, mrb_value obj, mrb_iv_foreach_func *func, void *p)
+{
+  if (!obj_iv_p(obj)) return;
+  iv_foreach(mrb, mrb_obj_ptr(obj)->iv, func, p);
+}
+
+static inline mrb_bool
+namespace_p(enum mrb_vtype tt)
+{
+  return tt == MRB_TT_CLASS || tt == MRB_TT_MODULE ? TRUE : FALSE;
+}
+
+static inline void
+assign_class_name(mrb_state *mrb, struct RObject *obj, mrb_sym sym, mrb_value v)
+{
+  if (namespace_p(obj->tt) && namespace_p(mrb_type(v))) {
+    struct RObject *c = mrb_obj_ptr(v);
+    if (obj != c && ISUPPER(mrb_sym2name(mrb, sym)[0])) {
+      mrb_sym id_classname = mrb_intern_lit(mrb, "__classname__");
+      mrb_value o = mrb_obj_iv_get(mrb, c, id_classname);
+
+      if (mrb_nil_p(o)) {
+        mrb_sym id_outer = mrb_intern_lit(mrb, "__outer__");
+        o = mrb_obj_iv_get(mrb, c, id_outer);
+
+        if (mrb_nil_p(o)) {
+          if ((struct RClass *)obj == mrb->object_class) {
+            mrb_obj_iv_set_force(mrb, c, id_classname, mrb_symbol_value(sym));
+          }
+          else {
+            mrb_obj_iv_set_force(mrb, c, id_outer, mrb_obj_value(obj));
+          }
+        }
+      }
+    }
   }
-  mrb_write_barrier(mrb, (struct RBasic*)obj);
-  iv_put(mrb, t, sym, v);
 }
 
 MRB_API void
@@ -300,28 +429,23 @@ mrb_iv_defined(mrb_state *mrb, mrb_value obj, mrb_sym sym)
   return mrb_obj_iv_defined(mrb, mrb_obj_ptr(obj), sym);
 }
 
-#define identchar(c) (ISALNUM(c) || (c) == '_' || !ISASCII(c))
-
 MRB_API mrb_bool
-mrb_iv_p(mrb_state *mrb, mrb_sym iv_name)
+mrb_iv_name_sym_p(mrb_state *mrb, mrb_sym iv_name)
 {
   const char *s;
-  mrb_int i, len;
+  mrb_int len;
 
   s = mrb_sym2name_len(mrb, iv_name, &len);
   if (len < 2) return FALSE;
   if (s[0] != '@') return FALSE;
-  if (s[1] == '@') return FALSE;
-  for (i=1; i<len; i++) {
-    if (!identchar(s[i])) return FALSE;
-  }
-  return TRUE;
+  if (ISDIGIT(s[1])) return FALSE;
+  return mrb_ident_p(s+1, len-1);
 }
 
 MRB_API void
-mrb_iv_check(mrb_state *mrb, mrb_sym iv_name)
+mrb_iv_name_sym_check(mrb_state *mrb, mrb_sym iv_name)
 {
-  if (!mrb_iv_p(mrb, iv_name)) {
+  if (!mrb_iv_name_sym_p(mrb, iv_name)) {
     mrb_name_error(mrb, iv_name, "'%S' is not allowed as an instance variable name", mrb_sym2str(mrb, iv_name));
   }
 }
@@ -401,27 +525,14 @@ mrb_iv_remove(mrb_state *mrb, mrb_value obj, mrb_sym sym)
     iv_tbl *t = mrb_obj_ptr(obj)->iv;
     mrb_value val;
 
-    if (t && iv_del(mrb, t, sym, &val)) {
+    mrb_check_frozen(mrb, mrb_obj_ptr(obj));
+    if (iv_del(mrb, t, sym, &val)) {
       return val;
     }
   }
   return mrb_undef_value();
 }
 
-mrb_value
-mrb_vm_iv_get(mrb_state *mrb, mrb_sym sym)
-{
-  /* get self */
-  return mrb_iv_get(mrb, mrb->c->stack[0], sym);
-}
-
-void
-mrb_vm_iv_set(mrb_state *mrb, mrb_sym sym, mrb_value v)
-{
-  /* get self */
-  mrb_iv_set(mrb, mrb->c->stack[0], sym, v);
-}
-
 static int
 iv_i(mrb_state *mrb, mrb_sym sym, mrb_value v, void *p)
 {
@@ -460,7 +571,7 @@ mrb_obj_instance_variables(mrb_state *mrb, mrb_value self)
   mrb_value ary;
 
   ary = mrb_ary_new(mrb);
-  if (obj_iv_p(self) && mrb_obj_ptr(self)->iv) {
+  if (obj_iv_p(self)) {
     iv_foreach(mrb, mrb_obj_ptr(self)->iv, iv_i, &ary);
   }
   return ary;
@@ -506,15 +617,13 @@ mrb_mod_class_variables(mrb_state *mrb, mrb_value mod)
   ary = mrb_ary_new(mrb);
   c = mrb_class_ptr(mod);
   while (c) {
-    if (c->iv) {
-      iv_foreach(mrb, c->iv, cv_i, &ary);
-    }
+    iv_foreach(mrb, c->iv, cv_i, &ary);
     c = c->super;
   }
   return ary;
 }
 
-MRB_API mrb_value
+mrb_value
 mrb_mod_cv_get(mrb_state *mrb, struct RClass *c, mrb_sym sym)
 {
   struct RClass * cls = c;
@@ -563,14 +672,13 @@ mrb_mod_cv_set(mrb_state *mrb, struct RClass *c, mrb_sym sym, mrb_value v)
   struct RClass * cls = c;
 
   while (c) {
-    if (c->iv) {
-      iv_tbl *t = c->iv;
+    iv_tbl *t = c->iv;
 
-      if (iv_get(mrb, t, sym, NULL)) {
-        mrb_write_barrier(mrb, (struct RBasic*)c);
-        iv_put(mrb, t, sym, v);
-        return;
-      }
+    if (iv_get(mrb, t, sym, NULL)) {
+      mrb_check_frozen(mrb, c);
+      iv_put(mrb, t, sym, v);
+      mrb_write_barrier(mrb, (struct RBasic*)c);
+      return;
     }
     c = c->super;
   }
@@ -595,12 +703,13 @@ mrb_mod_cv_set(mrb_state *mrb, struct RClass *c, mrb_sym sym, mrb_value v)
     c = cls;
   }
 
+  mrb_check_frozen(mrb, c);
   if (!c->iv) {
     c->iv = iv_new(mrb);
   }
 
-  mrb_write_barrier(mrb, (struct RBasic*)c);
   iv_put(mrb, c->iv, sym, v);
+  mrb_write_barrier(mrb, (struct RBasic*)c);
 }
 
 MRB_API void
@@ -609,14 +718,12 @@ mrb_cv_set(mrb_state *mrb, mrb_value mod, mrb_sym sym, mrb_value v)
   mrb_mod_cv_set(mrb, mrb_class_ptr(mod), sym, v);
 }
 
-MRB_API mrb_bool
+mrb_bool
 mrb_mod_cv_defined(mrb_state *mrb, struct RClass * c, mrb_sym sym)
 {
   while (c) {
-    if (c->iv) {
-      iv_tbl *t = c->iv;
-      if (iv_get(mrb, t, sym, NULL)) return TRUE;
-    }
+    iv_tbl *t = c->iv;
+    if (iv_get(mrb, t, sym, NULL)) return TRUE;
     c = c->super;
   }
 
@@ -662,24 +769,23 @@ mod_const_check(mrb_state *mrb, mrb_value mod)
 }
 
 static mrb_value
-const_get(mrb_state *mrb, struct RClass *base, mrb_sym sym, mrb_bool top)
+const_get(mrb_state *mrb, struct RClass *base, mrb_sym sym)
 {
   struct RClass *c = base;
   mrb_value v;
   mrb_bool retry = FALSE;
   mrb_value name;
-  struct RClass *oclass = mrb->object_class;
 
 L_RETRY:
   while (c) {
-    if (c->iv && (top || c != oclass || base == oclass)) {
+    if (c->iv) {
       if (iv_get(mrb, c->iv, sym, &v))
         return v;
     }
     c = c->super;
   }
   if (!retry && base->tt == MRB_TT_MODULE) {
-    c = oclass;
+    c = mrb->object_class;
     retry = TRUE;
     goto L_RETRY;
   }
@@ -691,7 +797,7 @@ MRB_API mrb_value
 mrb_const_get(mrb_state *mrb, mrb_value mod, mrb_sym sym)
 {
   mod_const_check(mrb, mod);
-  return const_get(mrb, mrb_class_ptr(mod), sym, FALSE);
+  return const_get(mrb, mrb_class_ptr(mod), sym);
 }
 
 mrb_value
@@ -703,27 +809,30 @@ mrb_vm_const_get(mrb_state *mrb, mrb_sym sym)
   struct RProc *proc;
 
   c = MRB_PROC_TARGET_CLASS(mrb->c->ci->proc);
-  if (c->iv && iv_get(mrb, c->iv, sym, &v)) {
+  if (iv_get(mrb, c->iv, sym, &v)) {
     return v;
   }
   c2 = c;
   while (c2 && c2->tt == MRB_TT_SCLASS) {
     mrb_value klass;
-    klass = mrb_obj_iv_get(mrb, (struct RObject *)c2,
-                           mrb_intern_lit(mrb, "__attached__"));
+
+    if (!iv_get(mrb, c2->iv, mrb_intern_lit(mrb, "__attached__"), &klass)) {
+      c2 = NULL;
+      break;
+    }
     c2 = mrb_class_ptr(klass);
   }
-  if (c2->tt == MRB_TT_CLASS || c2->tt == MRB_TT_MODULE) c = c2;
+  if (c2 && (c2->tt == MRB_TT_CLASS || c2->tt == MRB_TT_MODULE)) c = c2;
   mrb_assert(!MRB_PROC_CFUNC_P(mrb->c->ci->proc));
   proc = mrb->c->ci->proc;
   while (proc) {
     c2 = MRB_PROC_TARGET_CLASS(proc);
-    if (c2 && c2->iv && iv_get(mrb, c2->iv, sym, &v)) { 
+    if (c2 && iv_get(mrb, c2->iv, sym, &v)) {
       return v;
     }
     proc = proc->upper;
   }
-  return const_get(mrb, c, sym, TRUE);
+  return const_get(mrb, c, sym);
 }
 
 MRB_API void
@@ -796,9 +905,7 @@ mrb_mod_constants(mrb_state *mrb, mrb_value mod)
   mrb_get_args(mrb, "|b", &inherit);
   ary = mrb_ary_new(mrb);
   while (c) {
-    if (c->iv) {
-      iv_foreach(mrb, c->iv, const_i, &ary);
-    }
+    iv_foreach(mrb, c->iv, const_i, &ary);
     if (!inherit) break;
     c = c->super;
     if (c == mrb->object_class) break;
@@ -811,9 +918,6 @@ mrb_gv_get(mrb_state *mrb, mrb_sym sym)
 {
   mrb_value v;
 
-  if (!mrb->globals) {
-    return mrb_nil_value();
-  }
   if (iv_get(mrb, mrb->globals, sym, &v))
     return v;
   return mrb_nil_value();
@@ -825,20 +929,15 @@ mrb_gv_set(mrb_state *mrb, mrb_sym sym, mrb_value v)
   iv_tbl *t;
 
   if (!mrb->globals) {
-    t = mrb->globals = iv_new(mrb);
-  }
-  else {
-    t = mrb->globals;
+    mrb->globals = iv_new(mrb);
   }
+  t = mrb->globals;
   iv_put(mrb, t, sym, v);
 }
 
 MRB_API void
 mrb_gv_remove(mrb_state *mrb, mrb_sym sym)
 {
-  if (!mrb->globals) {
-    return;
-  }
   iv_del(mrb, mrb->globals, sym, NULL);
 }
 
@@ -867,18 +966,8 @@ mrb_f_global_variables(mrb_state *mrb, mrb_value self)
 {
   iv_tbl *t = mrb->globals;
   mrb_value ary = mrb_ary_new(mrb);
-  size_t i;
-  char buf[3];
 
-  if (t) {
-    iv_foreach(mrb, t, gv_i, &ary);
-  }
-  buf[0] = '$';
-  buf[2] = 0;
-  for (i = 1; i <= 9; ++i) {
-    buf[1] = (char)(i + '0');
-    mrb_ary_push(mrb, ary, mrb_symbol_value(mrb_intern(mrb, buf, 2)));
-  }
+  iv_foreach(mrb, t, gv_i, &ary);
   return ary;
 }
 
@@ -892,7 +981,7 @@ mrb_const_defined_0(mrb_state *mrb, mrb_value mod, mrb_sym id, mrb_bool exclude,
   tmp = klass;
 retry:
   while (tmp) {
-    if (tmp->iv && iv_get(mrb, tmp->iv, id, NULL)) {
+    if (iv_get(mrb, tmp->iv, id, NULL)) {
       return TRUE;
     }
     if (!recurse && (klass != mrb->object_class)) break;
@@ -928,25 +1017,25 @@ struct csym_arg {
   struct RClass *c;
   mrb_sym sym;
 };
- 
+
 static int
 csym_i(mrb_state *mrb, mrb_sym sym, mrb_value v, void *p)
 {
   struct csym_arg *a = (struct csym_arg*)p;
   struct RClass *c = a->c;
- 
+
   if (mrb_type(v) == c->tt && mrb_class_ptr(v) == c) {
     a->sym = sym;
     return 1;     /* stop iteration */
   }
   return 0;
 }
- 
+
 static mrb_sym
 find_class_sym(mrb_state *mrb, struct RClass *outer, struct RClass *c)
 {
   struct csym_arg arg;
- 
+
   if (!outer) return 0;
   if (outer == c) return 0;
   arg.c = c;
@@ -1009,8 +1098,24 @@ mrb_class_find_path(mrb_state *mrb, struct RClass *c)
 
   str = mrb_sym2name_len(mrb, name, &len);
   mrb_str_cat(mrb, path, str, len);
-  iv_del(mrb, c->iv, mrb_intern_lit(mrb, "__outer__"), NULL);
-  iv_put(mrb, c->iv, mrb_intern_lit(mrb, "__classname__"), path);
-  mrb_field_write_barrier_value(mrb, (struct RBasic*)c, path);
+  if (RSTRING_PTR(path)[0] != '#') {
+    iv_del(mrb, c->iv, mrb_intern_lit(mrb, "__outer__"), NULL);
+    iv_put(mrb, c->iv, mrb_intern_lit(mrb, "__classname__"), path);
+    mrb_field_write_barrier_value(mrb, (struct RBasic*)c, path);
+    path = mrb_str_dup(mrb, path);
+  }
   return path;
 }
+
+#define identchar(c) (ISALNUM(c) || (c) == '_' || !ISASCII(c))
+
+mrb_bool
+mrb_ident_p(const char *s, mrb_int len)
+{
+  mrb_int i;
+
+  for (i = 0; i < len; i++) {
+    if (!identchar(s[i])) return FALSE;
+  }
+  return TRUE;
+}
diff --git a/src/vm.c b/src/vm.c
index c9e923ee0..0a6d4af8d 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -55,7 +55,7 @@ void abort(void);
 
 /* Maximum depth of ecall() recursion. */
 #ifndef MRB_ECALL_DEPTH_MAX
-#define MRB_ECALL_DEPTH_MAX 32
+#define MRB_ECALL_DEPTH_MAX 512
 #endif
 
 /* Maximum stack depth. Should be set lower on memory constrained systems.
@@ -101,7 +101,7 @@ static inline void
 stack_clear(mrb_value *from, size_t count)
 {
 #ifndef MRB_NAN_BOXING
-  const mrb_value mrb_value_zero = { 0 };
+  const mrb_value mrb_value_zero = { { 0 } };
 
   while (count-- > 0) {
     *from++ = mrb_value_zero;
@@ -141,7 +141,7 @@ stack_init(mrb_state *mrb)
 }
 
 static inline void
-envadjust(mrb_state *mrb, mrb_value *oldbase, mrb_value *newbase, size_t size)
+envadjust(mrb_state *mrb, mrb_value *oldbase, mrb_value *newbase, size_t oldsize)
 {
   mrb_callinfo *ci = mrb->c->cibase;
 
@@ -151,7 +151,7 @@ envadjust(mrb_state *mrb, mrb_value *oldbase, mrb_value *newbase, size_t size)
     mrb_value *st;
 
     if (e && MRB_ENV_STACK_SHARED_P(e) &&
-        (st = e->stack) && oldbase <= st && st < oldbase+size) {
+        (st = e->stack) && oldbase <= st && st < oldbase+oldsize) {
       ptrdiff_t off = e->stack - oldbase;
 
       e->stack = newbase + off;
@@ -161,7 +161,7 @@ envadjust(mrb_state *mrb, mrb_value *oldbase, mrb_value *newbase, size_t size)
       e = MRB_PROC_ENV(ci->proc);
 
       if (e && MRB_ENV_STACK_SHARED_P(e) &&
-          (st = e->stack) && oldbase <= st && st < oldbase+size) {
+          (st = e->stack) && oldbase <= st && st < oldbase+oldsize) {
         ptrdiff_t off = e->stack - oldbase;
 
         e->stack = newbase + off;
@@ -176,7 +176,7 @@ envadjust(mrb_state *mrb, mrb_value *oldbase, mrb_value *newbase, size_t size)
 /** def rec ; $deep =+ 1 ; if $deep > 1000 ; return 0 ; end ; rec ; end  */
 
 static void
-stack_extend_alloc(mrb_state *mrb, int room)
+stack_extend_alloc(mrb_state *mrb, mrb_int room)
 {
   mrb_value *oldbase = mrb->c->stbase;
   mrb_value *newstack;
@@ -186,7 +186,7 @@ stack_extend_alloc(mrb_state *mrb, int room)
 
   if (off > size) size = off;
 #ifdef MRB_STACK_EXTEND_DOUBLING
-  if (room <= size)
+  if ((size_t)room <= size)
     size *= 2;
   else
     size += room;
@@ -205,7 +205,7 @@ stack_extend_alloc(mrb_state *mrb, int room)
     mrb_exc_raise(mrb, mrb_obj_value(mrb->stack_err));
   }
   stack_clear(&(newstack[oldsize]), size - oldsize);
-  envadjust(mrb, oldbase, newstack, size);
+  envadjust(mrb, oldbase, newstack, oldsize);
   mrb->c->stbase = newstack;
   mrb->c->stack = mrb->c->stbase + off;
   mrb->c->stend = mrb->c->stbase + size;
@@ -217,8 +217,8 @@ stack_extend_alloc(mrb_state *mrb, int room)
   }
 }
 
-static inline void
-stack_extend(mrb_state *mrb, int room)
+MRB_API void
+mrb_stack_extend(mrb_state *mrb, mrb_int room)
 {
   if (mrb->c->stack + room >= mrb->c->stend) {
     stack_extend_alloc(mrb, room);
@@ -333,11 +333,12 @@ ecall(mrb_state *mrb)
   struct REnv *env;
   ptrdiff_t cioff;
   int ai = mrb_gc_arena_save(mrb);
-  int i = --c->eidx;
+  uint16_t i = --c->eidx;
   int nregs;
 
   if (i<0) return;
-  if (ci - c->cibase > MRB_ECALL_DEPTH_MAX) {
+  /* restrict total call depth of ecall() */
+  if (++mrb->ecall_nest > MRB_ECALL_DEPTH_MAX) {
     mrb_exc_raise(mrb, mrb_obj_value(mrb->stack_err));
   }
   p = c->ensure[i];
@@ -356,7 +357,6 @@ ecall(mrb_state *mrb)
   ci->acc = CI_ACC_SKIP;
   ci->argc = 0;
   ci->proc = p;
-  ci->nregs = p->body.irep->nregs;
   ci->target_class = MRB_PROC_TARGET_CLASS(p);
   env = MRB_PROC_ENV(p);
   mrb_assert(env);
@@ -365,11 +365,15 @@ ecall(mrb_state *mrb)
   if (exc) {
     mrb_gc_protect(mrb, mrb_obj_value(exc));
   }
+  if (mrb->c->fib) {
+    mrb_gc_protect(mrb, mrb_obj_value(mrb->c->fib));
+  }
   mrb_run(mrb, p, env->stack[0]);
   mrb->c = c;
   c->ci = c->cibase + cioff;
   if (!mrb->exc) mrb->exc = exc;
   mrb_gc_arena_restore(mrb, ai);
+  mrb->ecall_nest--;
 }
 
 #ifndef MRB_FUNCALL_ARGC_MAX
@@ -396,6 +400,30 @@ mrb_funcall(mrb_state *mrb, mrb_value self, const char *name, mrb_int argc, ...)
   return mrb_funcall_argv(mrb, self, mid, argc, argv);
 }
 
+static int
+ci_nregs(mrb_callinfo *ci)
+{
+  struct RProc *p;
+  int n = 0;
+
+  if (!ci) return 3;
+  p = ci->proc;
+  if (!p) {
+    if (ci->argc < 0) return 3;
+    return ci->argc+2;
+  }
+  if (!MRB_PROC_CFUNC_P(p) && p->body.irep) {
+    n = p->body.irep->nregs;
+  }
+  if (ci->argc < 0) {
+    if (n < 3) n = 3; /* self + args + blk */
+  }
+  if (ci->argc > n) {
+    n = ci->argc + 2; /* self + blk */
+  }
+  return n;
+}
+
 MRB_API mrb_value
 mrb_funcall_with_block(mrb_state *mrb, mrb_value self, mrb_sym mid, mrb_int argc, const mrb_value *argv, mrb_value blk)
 {
@@ -426,13 +454,12 @@ mrb_funcall_with_block(mrb_state *mrb, mrb_value self, mrb_sym mid, mrb_int argc
     mrb_method_t m;
     struct RClass *c;
     mrb_callinfo *ci;
-    int n;
+    int n = ci_nregs(mrb->c->ci);
     ptrdiff_t voff = -1;
 
     if (!mrb->c->stack) {
       stack_init(mrb);
     }
-    n = mrb->c->ci->nregs;
     if (argc < 0) {
       mrb_raisef(mrb, E_ARGUMENT_ERROR, "negative argc for funcall (%S)", mrb_fixnum_value(argc));
     }
@@ -446,7 +473,7 @@ mrb_funcall_with_block(mrb_state *mrb, mrb_value self, mrb_sym mid, mrb_int argc
         mrb_method_missing(mrb, mid, self, args);
       }
       mrb_ary_unshift(mrb, args, mrb_symbol_value(mid));
-      stack_extend(mrb, n+2);
+      mrb_stack_extend(mrb, n+2);
       mrb->c->stack[n+1] = args;
       argc = -1;
     }
@@ -459,26 +486,25 @@ mrb_funcall_with_block(mrb_state *mrb, mrb_value self, mrb_sym mid, mrb_int argc
     ci->argc = (int)argc;
     ci->target_class = c;
     mrb->c->stack = mrb->c->stack + n;
+    if (argc < 0) argc = 1;
     if (mrb->c->stbase <= argv && argv < mrb->c->stend) {
       voff = argv - mrb->c->stbase;
     }
-    if (MRB_METHOD_CFUNC_P(m)) {
-      ci->nregs = (int)(argc + 2);
-      stack_extend(mrb, ci->nregs);
-    }
-    else if (argc >= CALL_MAXARGS) {
+    if (argc >= CALL_MAXARGS) {
       mrb_value args = mrb_ary_new_from_values(mrb, argc, argv);
-      stack_extend(mrb, ci->nregs+2);
+
       mrb->c->stack[1] = args;
       ci->argc = -1;
       argc = 1;
     }
-    else {
+    mrb_stack_extend(mrb, argc + 2);
+    if (MRB_METHOD_PROC_P(m)) {
       struct RProc *p = MRB_METHOD_PROC(m);
+
       ci->proc = p;
-      if (argc < 0) argc = 1;
-      ci->nregs = (int)(p->body.irep->nregs + argc);
-      stack_extend(mrb, ci->nregs);
+      if (!MRB_PROC_CFUNC_P(p)) {
+        mrb_stack_extend(mrb, p->body.irep->nregs + argc);
+      }
     }
     if (voff >= 0) {
       argv = mrb->c->stbase + voff;
@@ -493,9 +519,6 @@ mrb_funcall_with_block(mrb_state *mrb, mrb_value self, mrb_sym mid, mrb_int argc
       int ai = mrb_gc_arena_save(mrb);
 
       ci->acc = CI_ACC_DIRECT;
-      if (MRB_METHOD_PROC_P(m)) {
-        ci->proc = MRB_METHOD_PROC(m);
-      }
       val = MRB_METHOD_CFUNC(m)(mrb, self);
       mrb->c->stack = mrb->c->ci->stackent;
       cipop(mrb);
@@ -520,28 +543,25 @@ mrb_value
 mrb_exec_irep(mrb_state *mrb, mrb_value self, struct RProc *p)
 {
   mrb_callinfo *ci = mrb->c->ci;
-  int keep;
+  int keep, nregs;
 
   mrb->c->stack[0] = self;
   ci->proc = p;
   if (MRB_PROC_CFUNC_P(p)) {
     return MRB_PROC_CFUNC(p)(mrb, self);
   }
-  ci->nregs = p->body.irep->nregs;
-  ci->env = MRB_PROC_ENV(p);
-  if (ci->env) ci->env->stack[0] = self;
+  nregs = p->body.irep->nregs;
   if (ci->argc < 0) keep = 3;
   else keep = ci->argc + 2;
-  if (ci->nregs < keep) {
-    stack_extend(mrb, keep);
+  if (nregs < keep) {
+    mrb_stack_extend(mrb, keep);
   }
   else {
-    stack_extend(mrb, ci->nregs);
-    stack_clear(mrb->c->stack+keep, ci->nregs-keep);
+    mrb_stack_extend(mrb, nregs);
+    stack_clear(mrb->c->stack+keep, nregs-keep);
   }
 
   ci = cipush(mrb);
-  ci->nregs = 0;
   ci->target_class = 0;
   ci->pc = p->body.irep->iseq;
   ci->stackent = mrb->c->stack;
@@ -569,7 +589,7 @@ mrb_exec_irep(mrb_state *mrb, mrb_value self, struct RProc *p)
  *     k = Klass.new
  *     k.send :hello, "gentle", "readers"   #=> "Hello gentle readers"
  */
-MRB_API mrb_value
+mrb_value
 mrb_f_send(mrb_state *mrb, mrb_value self)
 {
   mrb_sym name;
@@ -620,6 +640,7 @@ eval_under(mrb_state *mrb, mrb_value self, mrb_value blk, struct RClass *c)
 {
   struct RProc *p;
   mrb_callinfo *ci;
+  int nregs;
 
   if (mrb_nil_p(blk)) {
     mrb_raise(mrb, E_ARGUMENT_ERROR, "no block given");
@@ -635,19 +656,19 @@ eval_under(mrb_state *mrb, mrb_value self, mrb_value blk, struct RClass *c)
   ci->argc = 1;
   ci->mid = ci[-1].mid;
   if (MRB_PROC_CFUNC_P(p)) {
-    stack_extend(mrb, 3);
+    mrb_stack_extend(mrb, 3);
     mrb->c->stack[0] = self;
     mrb->c->stack[1] = self;
     mrb->c->stack[2] = mrb_nil_value();
     return MRB_PROC_CFUNC(p)(mrb, self);
   }
-  ci->nregs = p->body.irep->nregs;
-  stack_extend(mrb, (ci->nregs < 3) ? 3 : ci->nregs);
+  nregs = p->body.irep->nregs;
+  if (nregs < 3) nregs = 3;
+  mrb_stack_extend(mrb, nregs);
   mrb->c->stack[0] = self;
   mrb->c->stack[1] = self;
-  mrb->c->stack[2] = mrb_nil_value();
+  stack_clear(mrb->c->stack+2, nregs-2);
   ci = cipush(mrb);
-  ci->nregs = 0;
   ci->target_class = 0;
   ci->pc = p->body.irep->iseq;
   ci->stackent = mrb->c->stack;
@@ -730,13 +751,15 @@ mrb_yield_with_class(mrb_state *mrb, mrb_value b, mrb_int argc, const mrb_value
   struct RProc *p;
   mrb_sym mid = mrb->c->ci->mid;
   mrb_callinfo *ci;
-  int n = mrb->c->ci->nregs;
   mrb_value val;
+  int n;
 
   if (mrb_nil_p(b)) {
     mrb_raise(mrb, E_ARGUMENT_ERROR, "no block given");
   }
-  if (mrb->c->ci - mrb->c->cibase > MRB_FUNCALL_DEPTH_MAX) {
+  ci = mrb->c->ci;
+  n = ci_nregs(ci);
+  if (ci - mrb->c->cibase > MRB_FUNCALL_DEPTH_MAX) {
     mrb_exc_raise(mrb, mrb_obj_value(mrb->stack_err));
   }
   p = mrb_proc_ptr(b);
@@ -747,9 +770,9 @@ mrb_yield_with_class(mrb_state *mrb, mrb_value b, mrb_int argc, const mrb_value
   ci->argc = (int)argc;
   ci->target_class = c;
   ci->acc = CI_ACC_SKIP;
+  n = MRB_PROC_CFUNC_P(p) ? (int)(argc+2) : p->body.irep->nregs;
   mrb->c->stack = mrb->c->stack + n;
-  ci->nregs = MRB_PROC_CFUNC_P(p) ? (int)(argc+2) : p->body.irep->nregs;
-  stack_extend(mrb, ci->nregs);
+  mrb_stack_extend(mrb, n);
 
   mrb->c->stack[0] = self;
   if (argc > 0) {
@@ -800,38 +823,13 @@ mrb_yield_cont(mrb_state *mrb, mrb_value b, mrb_value self, mrb_int argc, const
   p = mrb_proc_ptr(b);
   ci = mrb->c->ci;
 
-  stack_extend(mrb, 3);
+  mrb_stack_extend(mrb, 3);
   mrb->c->stack[1] = mrb_ary_new_from_values(mrb, argc, argv);
   mrb->c->stack[2] = mrb_nil_value();
   ci->argc = -1;
   return mrb_exec_irep(mrb, self, p);
 }
 
-mrb_value
-mrb_mod_s_nesting(mrb_state *mrb, mrb_value mod)
-{
-  struct RProc *proc;
-  mrb_value ary;
-  struct RClass *c = NULL;
-
-  mrb_get_args(mrb, "");
-  ary = mrb_ary_new(mrb);
-  proc = mrb->c->ci[-1].proc;   /* callee proc */
-  mrb_assert(!MRB_PROC_CFUNC_P(proc));
-  while (proc) {
-    if (MRB_PROC_SCOPE_P(proc)) {
-      struct RClass *c2 = MRB_PROC_TARGET_CLASS(proc);
-
-      if (c2 != c) {
-        c = c2;
-        mrb_ary_push(mrb, ary, mrb_obj_value(c));
-      }
-    }
-    proc = proc->upper;
-  }
-  return ary;
-}
-
 static struct RBreak*
 break_new(mrb_state *mrb, struct RProc *p, mrb_value val)
 {
@@ -892,8 +890,8 @@ argnum_error(mrb_state *mrb, mrb_int num)
   mrb_exc_set(mrb, exc);
 }
 
-#define ERR_PC_SET(mrb, pc) mrb->c->ci->err = pc;
-#define ERR_PC_CLR(mrb)     mrb->c->ci->err = 0;
+#define ERR_PC_SET(mrb) mrb->c->ci->err = pc0;
+#define ERR_PC_CLR(mrb) mrb->c->ci->err = 0;
 #ifdef MRB_ENABLE_DEBUG_HOOK
 #define CODE_FETCH_HOOK(mrb, irep, pc, regs) if ((mrb)->code_fetch_hook) (mrb)->code_fetch_hook((mrb), (irep), (pc), (regs));
 #else
@@ -906,25 +904,26 @@ argnum_error(mrb_state *mrb, mrb_int num)
 #define BYTECODE_DECODER(x) (x)
 #endif
 
-
+#ifndef MRB_DISABLE_DIRECT_THREADING
 #if defined __GNUC__ || defined __clang__ || defined __INTEL_COMPILER
 #define DIRECT_THREADED
 #endif
+#endif /* ifndef MRB_DISABLE_DIRECT_THREADING */
 
 #ifndef DIRECT_THREADED
 
-#define INIT_DISPATCH for (;;) { i = BYTECODE_DECODER(*pc); CODE_FETCH_HOOK(mrb, irep, pc, regs); switch (GET_OPCODE(i)) {
-#define CASE(op) case op:
-#define NEXT pc++; break
-#define JUMP break
+#define INIT_DISPATCH for (;;) { insn = BYTECODE_DECODER(*pc); CODE_FETCH_HOOK(mrb, irep, pc, regs); switch (insn) {
+#define CASE(insn,ops) case insn: pc0=pc++; FETCH_ ## ops ();; L_ ## insn ## _BODY:
+#define NEXT break
+#define JUMP NEXT
 #define END_DISPATCH }}
 
 #else
 
 #define INIT_DISPATCH JUMP; return mrb_nil_value();
-#define CASE(op) L_ ## op:
-#define NEXT i=BYTECODE_DECODER(*++pc); CODE_FETCH_HOOK(mrb, irep, pc, regs); goto *optable[GET_OPCODE(i)]
-#define JUMP i=BYTECODE_DECODER(*pc); CODE_FETCH_HOOK(mrb, irep, pc, regs); goto *optable[GET_OPCODE(i)]
+#define CASE(insn,ops) L_ ## insn: pc0=pc++; FETCH_ ## ops (); L_ ## insn ## _BODY:
+#define NEXT insn=BYTECODE_DECODER(*pc); CODE_FETCH_HOOK(mrb, irep, pc, regs); goto *optable[insn]
+#define JUMP NEXT
 
 #define END_DISPATCH
 
@@ -944,51 +943,57 @@ mrb_vm_run(mrb_state *mrb, struct RProc *proc, mrb_value self, unsigned int stac
   }
   if (stack_keep > nregs)
     nregs = stack_keep;
-  stack_extend(mrb, nregs);
+  mrb_stack_extend(mrb, nregs);
   stack_clear(c->stack + stack_keep, nregs - stack_keep);
   c->stack[0] = self;
   result = mrb_vm_exec(mrb, proc, irep->iseq);
-  if (c->ci - c->cibase > cioff) {
+  if (mrb->c != c) {
+    if (mrb->c->fib) {
+      mrb_write_barrier(mrb, (struct RBasic*)mrb->c->fib);
+    }
+    mrb->c = c;
+  }
+  else if (c->ci - c->cibase > cioff) {
     c->ci = c->cibase + cioff;
   }
-  mrb->c = c;
   return result;
 }
 
+static mrb_bool
+check_target_class(mrb_state *mrb)
+{
+  if (!mrb->c->ci->target_class) {
+    mrb_value exc = mrb_exc_new_str_lit(mrb, E_TYPE_ERROR, "no target class or module");
+    mrb_exc_set(mrb, exc);
+    return FALSE;
+  }
+  return TRUE;
+}
+
+void mrb_hash_check_kdict(mrb_state *mrb, mrb_value self);
+
 MRB_API mrb_value
 mrb_vm_exec(mrb_state *mrb, struct RProc *proc, mrb_code *pc)
 {
-  /* mrb_assert(mrb_proc_cfunc_p(proc)) */
+  /* mrb_assert(MRB_PROC_CFUNC_P(proc)) */
+  mrb_code *pc0 = pc;
   mrb_irep *irep = proc->body.irep;
   mrb_value *pool = irep->pool;
   mrb_sym *syms = irep->syms;
-  mrb_code i;
+  mrb_code insn;
   int ai = mrb_gc_arena_save(mrb);
   struct mrb_jmpbuf *prev_jmp = mrb->jmp;
   struct mrb_jmpbuf c_jmp;
+  uint32_t a;
+  uint16_t b;
+  uint8_t c;
+  mrb_sym mid;
 
 #ifdef DIRECT_THREADED
   static void *optable[] = {
-    &&L_OP_NOP, &&L_OP_MOVE,
-    &&L_OP_LOADL, &&L_OP_LOADI, &&L_OP_LOADSYM, &&L_OP_LOADNIL,
-    &&L_OP_LOADSELF, &&L_OP_LOADT, &&L_OP_LOADF,
-    &&L_OP_GETGLOBAL, &&L_OP_SETGLOBAL, &&L_OP_GETSPECIAL, &&L_OP_SETSPECIAL,
-    &&L_OP_GETIV, &&L_OP_SETIV, &&L_OP_GETCV, &&L_OP_SETCV,
-    &&L_OP_GETCONST, &&L_OP_SETCONST, &&L_OP_GETMCNST, &&L_OP_SETMCNST,
-    &&L_OP_GETUPVAR, &&L_OP_SETUPVAR,
-    &&L_OP_JMP, &&L_OP_JMPIF, &&L_OP_JMPNOT,
-    &&L_OP_ONERR, &&L_OP_RESCUE, &&L_OP_POPERR, &&L_OP_RAISE, &&L_OP_EPUSH, &&L_OP_EPOP,
-    &&L_OP_SEND, &&L_OP_SENDB, &&L_OP_FSEND,
-    &&L_OP_CALL, &&L_OP_SUPER, &&L_OP_ARGARY, &&L_OP_ENTER,
-    &&L_OP_KARG, &&L_OP_KDICT, &&L_OP_RETURN, &&L_OP_TAILCALL, &&L_OP_BLKPUSH,
-    &&L_OP_ADD, &&L_OP_ADDI, &&L_OP_SUB, &&L_OP_SUBI, &&L_OP_MUL, &&L_OP_DIV,
-    &&L_OP_EQ, &&L_OP_LT, &&L_OP_LE, &&L_OP_GT, &&L_OP_GE,
-    &&L_OP_ARRAY, &&L_OP_ARYCAT, &&L_OP_ARYPUSH, &&L_OP_AREF, &&L_OP_ASET, &&L_OP_APOST,
-    &&L_OP_STRING, &&L_OP_STRCAT, &&L_OP_HASH,
-    &&L_OP_LAMBDA, &&L_OP_RANGE, &&L_OP_OCLASS,
-    &&L_OP_CLASS, &&L_OP_MODULE, &&L_OP_EXEC,
-    &&L_OP_METHOD, &&L_OP_SCLASS, &&L_OP_TCLASS,
-    &&L_OP_DEBUG, &&L_OP_STOP, &&L_OP_ERR,
+#define OPCODE(x,_) &&L_OP_ ## x,
+#include "mruby/ops.h"
+#undef OPCODE
   };
 #endif
 
@@ -999,35 +1004,29 @@ RETRY_TRY_BLOCK:
 
   if (exc_catched) {
     exc_catched = FALSE;
+    mrb_gc_arena_restore(mrb, ai);
     if (mrb->exc && mrb->exc->tt == MRB_TT_BREAK)
       goto L_BREAK;
     goto L_RAISE;
   }
   mrb->jmp = &c_jmp;
   mrb->c->ci->proc = proc;
-  mrb->c->ci->nregs = irep->nregs;
 
 #define regs (mrb->c->stack)
   INIT_DISPATCH {
-    CASE(OP_NOP) {
+    CASE(OP_NOP, Z) {
       /* do nothing */
       NEXT;
     }
 
-    CASE(OP_MOVE) {
-      /* A B    R(A) := R(B) */
-      int a = GETARG_A(i);
-      int b = GETARG_B(i);
+    CASE(OP_MOVE, BB) {
       regs[a] = regs[b];
       NEXT;
     }
 
-    CASE(OP_LOADL) {
-      /* A Bx   R(A) := Pool(Bx) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
+    CASE(OP_LOADL, BB) {
 #ifdef MRB_WORD_BOXING
-      mrb_value val = pool[bx];
+      mrb_value val = pool[b];
 #ifndef MRB_WITHOUT_FLOAT
       if (mrb_float_p(val)) {
         val = mrb_float_value(mrb, mrb_float(val));
@@ -1035,167 +1034,138 @@ RETRY_TRY_BLOCK:
 #endif
       regs[a] = val;
 #else
-      regs[a] = pool[bx];
+      regs[a] = pool[b];
 #endif
       NEXT;
     }
 
-    CASE(OP_LOADI) {
-      /* A sBx  R(A) := sBx */
-      int a = GETARG_A(i);
-      mrb_int bx = GETARG_sBx(i);
-      SET_INT_VALUE(regs[a], bx);
+    CASE(OP_LOADI, BB) {
+      SET_INT_VALUE(regs[a], b);
+      NEXT;
+    }
+
+    CASE(OP_LOADINEG, BB) {
+      SET_INT_VALUE(regs[a], -b);
+      NEXT;
+    }
+
+    CASE(OP_LOADI__1,B) goto L_LOADI;
+    CASE(OP_LOADI_0,B) goto L_LOADI;
+    CASE(OP_LOADI_1,B) goto L_LOADI;
+    CASE(OP_LOADI_2,B) goto L_LOADI;
+    CASE(OP_LOADI_3,B) goto L_LOADI;
+    CASE(OP_LOADI_4,B) goto L_LOADI;
+    CASE(OP_LOADI_5,B) goto L_LOADI;
+    CASE(OP_LOADI_6,B) goto L_LOADI;
+    CASE(OP_LOADI_7, B) {
+    L_LOADI:
+      SET_INT_VALUE(regs[a], (mrb_int)insn - (mrb_int)OP_LOADI_0);
       NEXT;
     }
 
-    CASE(OP_LOADSYM) {
-      /* A Bx   R(A) := Syms(Bx) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      SET_SYM_VALUE(regs[a], syms[bx]);
+    CASE(OP_LOADSYM, BB) {
+      SET_SYM_VALUE(regs[a], syms[b]);
       NEXT;
     }
 
-    CASE(OP_LOADSELF) {
-      /* A      R(A) := self */
-      int a = GETARG_A(i);
+    CASE(OP_LOADNIL, B) {
+      SET_NIL_VALUE(regs[a]);
+      NEXT;
+    }
+
+    CASE(OP_LOADSELF, B) {
       regs[a] = regs[0];
       NEXT;
     }
 
-    CASE(OP_LOADT) {
-      /* A      R(A) := true */
-      int a = GETARG_A(i);
+    CASE(OP_LOADT, B) {
       SET_TRUE_VALUE(regs[a]);
       NEXT;
     }
 
-    CASE(OP_LOADF) {
-      /* A      R(A) := false */
-      int a = GETARG_A(i);
+    CASE(OP_LOADF, B) {
       SET_FALSE_VALUE(regs[a]);
       NEXT;
     }
 
-    CASE(OP_GETGLOBAL) {
-      /* A Bx   R(A) := getglobal(Syms(Bx)) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      mrb_value val = mrb_gv_get(mrb, syms[bx]);
+    CASE(OP_GETGV, BB) {
+      mrb_value val = mrb_gv_get(mrb, syms[b]);
       regs[a] = val;
       NEXT;
     }
 
-    CASE(OP_SETGLOBAL) {
-      /* A Bx   setglobal(Syms(Bx), R(A)) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      mrb_gv_set(mrb, syms[bx], regs[a]);
+    CASE(OP_SETGV, BB) {
+      mrb_gv_set(mrb, syms[b], regs[a]);
       NEXT;
     }
 
-    CASE(OP_GETSPECIAL) {
-      /* A Bx   R(A) := Special[Bx] */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      mrb_value val = mrb_vm_special_get(mrb, bx);
+    CASE(OP_GETSV, BB) {
+      mrb_value val = mrb_vm_special_get(mrb, b);
       regs[a] = val;
       NEXT;
     }
 
-    CASE(OP_SETSPECIAL) {
-      /* A Bx   Special[Bx] := R(A) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      mrb_vm_special_set(mrb, bx, regs[a]);
+    CASE(OP_SETSV, BB) {
+      mrb_vm_special_set(mrb, b, regs[a]);
       NEXT;
     }
 
-    CASE(OP_GETIV) {
-      /* A Bx   R(A) := ivget(Bx) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      mrb_value val = mrb_vm_iv_get(mrb, syms[bx]);
-      regs[a] = val;
+    CASE(OP_GETIV, BB) {
+      regs[a] = mrb_iv_get(mrb, regs[0], syms[b]);
       NEXT;
     }
 
-    CASE(OP_SETIV) {
-      /* A Bx   ivset(Syms(Bx),R(A)) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      mrb_vm_iv_set(mrb, syms[bx], regs[a]);
+    CASE(OP_SETIV, BB) {
+      mrb_iv_set(mrb, regs[0], syms[b], regs[a]);
       NEXT;
     }
 
-    CASE(OP_GETCV) {
-      /* A Bx   R(A) := cvget(Syms(Bx)) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
+    CASE(OP_GETCV, BB) {
       mrb_value val;
-      ERR_PC_SET(mrb, pc);
-      val = mrb_vm_cv_get(mrb, syms[bx]);
+      ERR_PC_SET(mrb);
+      val = mrb_vm_cv_get(mrb, syms[b]);
       ERR_PC_CLR(mrb);
       regs[a] = val;
       NEXT;
     }
 
-    CASE(OP_SETCV) {
-      /* A Bx   cvset(Syms(Bx),R(A)) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      mrb_vm_cv_set(mrb, syms[bx], regs[a]);
+    CASE(OP_SETCV, BB) {
+      mrb_vm_cv_set(mrb, syms[b], regs[a]);
       NEXT;
     }
 
-    CASE(OP_GETCONST) {
-      /* A Bx    R(A) := constget(Syms(Bx)) */
+    CASE(OP_GETCONST, BB) {
       mrb_value val;
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      mrb_sym sym = syms[bx];
+      mrb_sym sym = syms[b];
 
-      ERR_PC_SET(mrb, pc);
+      ERR_PC_SET(mrb);
       val = mrb_vm_const_get(mrb, sym);
       ERR_PC_CLR(mrb);
       regs[a] = val;
       NEXT;
     }
 
-    CASE(OP_SETCONST) {
-      /* A Bx   constset(Syms(Bx),R(A)) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      mrb_vm_const_set(mrb, syms[bx], regs[a]);
+    CASE(OP_SETCONST, BB) {
+      mrb_vm_const_set(mrb, syms[b], regs[a]);
       NEXT;
     }
 
-    CASE(OP_GETMCNST) {
-      /* A Bx   R(A) := R(A)::Syms(Bx) */
+    CASE(OP_GETMCNST, BB) {
       mrb_value val;
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
 
-      ERR_PC_SET(mrb, pc);
-      val = mrb_const_get(mrb, regs[a], syms[bx]);
+      ERR_PC_SET(mrb);
+      val = mrb_const_get(mrb, regs[a], syms[b]);
       ERR_PC_CLR(mrb);
       regs[a] = val;
       NEXT;
     }
 
-    CASE(OP_SETMCNST) {
-      /* A Bx    R(A+1)::Syms(Bx) := R(A) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      mrb_const_set(mrb, regs[a+1], syms[bx], regs[a]);
+    CASE(OP_SETMCNST, BB) {
+      mrb_const_set(mrb, regs[a+1], syms[b], regs[a]);
       NEXT;
     }
 
-    CASE(OP_GETUPVAR) {
-      /* A B C  R(A) := uvget(B,C) */
-      int a = GETARG_A(i);
-      int b = GETARG_B(i);
-      int c = GETARG_C(i);
+    CASE(OP_GETUPVAR, BBB) {
       mrb_value *regs_a = regs + a;
       struct REnv *e = uvenv(mrb, c);
 
@@ -1208,12 +1178,7 @@ RETRY_TRY_BLOCK:
       NEXT;
     }
 
-    CASE(OP_SETUPVAR) {
-      /* A B C  uvset(B,C,R(A)) */
-      int a = GETARG_A(i);
-      int b = GETARG_B(i);
-      int c = GETARG_C(i);
-
+    CASE(OP_SETUPVAR, BBB) {
       struct REnv *e = uvenv(mrb, c);
 
       if (e) {
@@ -1227,127 +1192,126 @@ RETRY_TRY_BLOCK:
       NEXT;
     }
 
-    CASE(OP_JMP) {
-      /* sBx    pc+=sBx */
-      int sbx = GETARG_sBx(i);
-      pc += sbx;
+    CASE(OP_JMP, S) {
+      pc = irep->iseq+a;
       JUMP;
     }
-
-    CASE(OP_JMPIF) {
-      /* A sBx  if R(A) pc+=sBx */
-      int a = GETARG_A(i);
-      int sbx = GETARG_sBx(i);
+    CASE(OP_JMPIF, BS) {
       if (mrb_test(regs[a])) {
-        pc += sbx;
+        pc = irep->iseq+b;
         JUMP;
       }
       NEXT;
     }
-
-    CASE(OP_JMPNOT) {
-      /* A sBx  if !R(A) pc+=sBx */
-      int a = GETARG_A(i);
-      int sbx = GETARG_sBx(i);
+    CASE(OP_JMPNOT, BS) {
       if (!mrb_test(regs[a])) {
-        pc += sbx;
+        pc = irep->iseq+b;
+        JUMP;
+      }
+      NEXT;
+    }
+    CASE(OP_JMPNIL, BS) {
+      if (mrb_nil_p(regs[a])) {
+        pc = irep->iseq+b;
         JUMP;
       }
       NEXT;
     }
 
-    CASE(OP_ONERR) {
-      /* sBx    pc+=sBx on exception */
-      int sbx = GETARG_sBx(i);
+    CASE(OP_ONERR, S) {
+      /* check rescue stack */
+      if (mrb->c->ci->ridx == UINT16_MAX-1) {
+        mrb_value exc = mrb_exc_new_str_lit(mrb, E_RUNTIME_ERROR, "too many nested rescues");
+        mrb_exc_set(mrb, exc);
+        goto L_RAISE;
+      }
+      /* expand rescue stack */
       if (mrb->c->rsize <= mrb->c->ci->ridx) {
         if (mrb->c->rsize == 0) mrb->c->rsize = RESCUE_STACK_INIT_SIZE;
-        else mrb->c->rsize *= 2;
-        mrb->c->rescue = (mrb_code **)mrb_realloc(mrb, mrb->c->rescue, sizeof(mrb_code*) * mrb->c->rsize);
+        else {
+          mrb->c->rsize *= 2;
+          if (mrb->c->rsize <= mrb->c->ci->ridx) {
+            mrb->c->rsize = UINT16_MAX;
+          }
+        }
+        mrb->c->rescue = (uint16_t*)mrb_realloc(mrb, mrb->c->rescue, sizeof(uint16_t)*mrb->c->rsize);
       }
-      mrb->c->rescue[mrb->c->ci->ridx++] = pc + sbx;
+      /* push rescue stack */
+      mrb->c->rescue[mrb->c->ci->ridx++] = a;
       NEXT;
     }
 
-    CASE(OP_RESCUE) {
-      /* A B    R(A) := exc; clear(exc); R(B) := matched (bool) */
-      int a = GETARG_A(i);
-      int b = GETARG_B(i);
-      int c = GETARG_C(i);
-      mrb_value exc;
-
-      if (c == 0) {
-        exc = mrb_obj_value(mrb->exc);
-        mrb->exc = 0;
-      }
-      else {           /* continued; exc taken from R(A) */
-        exc = regs[a];
-      }
-      if (b != 0) {
-        mrb_value e = regs[b];
-        struct RClass *ec;
+    CASE(OP_EXCEPT, B) {
+      mrb_value exc = mrb_obj_value(mrb->exc);
+      mrb->exc = 0;
+      regs[a] = exc;
+      NEXT;
+    }
+    CASE(OP_RESCUE, BB) {
+      mrb_value exc = regs[a];  /* exc on stack */
+      mrb_value e = regs[b];
+      struct RClass *ec;
 
-        switch (mrb_type(e)) {
-        case MRB_TT_CLASS:
-        case MRB_TT_MODULE:
-          break;
-        default:
-          {
-            mrb_value exc;
+      switch (mrb_type(e)) {
+      case MRB_TT_CLASS:
+      case MRB_TT_MODULE:
+        break;
+      default:
+        {
+          mrb_value exc;
 
-            exc = mrb_exc_new_str_lit(mrb, E_TYPE_ERROR,
-                  "class or module required for rescue clause");
-            mrb_exc_set(mrb, exc);
-            goto L_RAISE;
-          }
+          exc = mrb_exc_new_str_lit(mrb, E_TYPE_ERROR,
+                                    "class or module required for rescue clause");
+          mrb_exc_set(mrb, exc);
+          goto L_RAISE;
         }
-        ec = mrb_class_ptr(e);
-        regs[b] = mrb_bool_value(mrb_obj_is_kind_of(mrb, exc, ec));
-      }
-      if (a != 0 && c == 0) {
-        regs[a] = exc;
       }
+      ec = mrb_class_ptr(e);
+      regs[b] = mrb_bool_value(mrb_obj_is_kind_of(mrb, exc, ec));
       NEXT;
     }
 
-    CASE(OP_POPERR) {
-      /* A      A.times{rescue_pop()} */
-      int a = GETARG_A(i);
-
+    CASE(OP_POPERR, B) {
       mrb->c->ci->ridx -= a;
       NEXT;
     }
 
-    CASE(OP_RAISE) {
-      /* A      raise(R(A)) */
-      int a = GETARG_A(i);
-
+    CASE(OP_RAISE, B) {
       mrb_exc_set(mrb, regs[a]);
       goto L_RAISE;
     }
 
-    CASE(OP_EPUSH) {
-      /* Bx     ensure_push(SEQ[Bx]) */
-      int bx = GETARG_Bx(i);
+    CASE(OP_EPUSH, B) {
       struct RProc *p;
 
-      p = mrb_closure_new(mrb, irep->reps[bx]);
-      /* push ensure_stack */
+      p = mrb_closure_new(mrb, irep->reps[a]);
+      /* check ensure stack */
+      if (mrb->c->eidx == UINT16_MAX-1) {
+        mrb_value exc = mrb_exc_new_str_lit(mrb, E_RUNTIME_ERROR, "too many nested ensures");
+        mrb_exc_set(mrb, exc);
+        goto L_RAISE;
+      }
+      /* expand ensure stack */
       if (mrb->c->esize <= mrb->c->eidx+1) {
         if (mrb->c->esize == 0) mrb->c->esize = ENSURE_STACK_INIT_SIZE;
-        else mrb->c->esize *= 2;
-        mrb->c->ensure = (struct RProc **)mrb_realloc(mrb, mrb->c->ensure, sizeof(struct RProc*) * mrb->c->esize);
+        else {
+          mrb->c->esize *= 2;
+          if (mrb->c->esize <= mrb->c->eidx) {
+            mrb->c->esize = UINT16_MAX;
+          }
+        }
+        mrb->c->ensure = (struct RProc**)mrb_realloc(mrb, mrb->c->ensure, sizeof(struct RProc*)*mrb->c->esize);
       }
+      /* push ensure stack */
       mrb->c->ensure[mrb->c->eidx++] = p;
       mrb->c->ensure[mrb->c->eidx] = NULL;
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
 
-    CASE(OP_EPOP) {
-      /* A      A.times{ensure_pop().call} */
-      int a = GETARG_A(i);
+    CASE(OP_EPOP, B) {
       mrb_callinfo *ci = mrb->c->ci;
-      int n, epos = ci->epos;
+      unsigned int n, epos = ci->epos;
       mrb_value self = regs[0];
       struct RClass *target_class = ci->target_class;
 
@@ -1355,10 +1319,11 @@ RETRY_TRY_BLOCK:
         NEXT;
       }
 
-      if (a > mrb->c->eidx - epos)
+      if (a > (int)mrb->c->eidx - epos)
         a = mrb->c->eidx - epos;
-      pc = pc + 1;
       for (n=0; n<a; n++) {
+        int nregs = irep->nregs;
+
         proc = mrb->c->ensure[epos+n];
         mrb->c->ensure[epos+n] = NULL;
         if (proc == NULL) continue;
@@ -1368,12 +1333,11 @@ RETRY_TRY_BLOCK:
         ci->argc = 0;
         ci->proc = proc;
         ci->stackent = mrb->c->stack;
-        ci->nregs = irep->nregs;
         ci->target_class = target_class;
         ci->pc = pc;
-        ci->acc = ci[-1].nregs;
+        ci->acc = nregs;
         mrb->c->stack += ci->acc;
-        stack_extend(mrb, ci->nregs);
+        mrb_stack_extend(mrb, irep->nregs);
         regs[0] = self;
         pc = irep->iseq;
       }
@@ -1383,63 +1347,69 @@ RETRY_TRY_BLOCK:
       JUMP;
     }
 
-    CASE(OP_LOADNIL) {
-      /* A     R(A) := nil */
-      int a = GETARG_A(i);
+    CASE(OP_SENDV, BB) {
+      c = CALL_MAXARGS;
+      goto L_SEND;
+    };
 
-      SET_NIL_VALUE(regs[a]);
-      NEXT;
-    }
+    CASE(OP_SENDVB, BB) {
+      c = CALL_MAXARGS;
+      goto L_SENDB;
+    };
 
-    CASE(OP_SENDB) {
-      /* A B C  R(A) := call(R(A),Syms(B),R(A+1),...,R(A+C),&R(A+C+1))*/
-      /* fall through */
+    CASE(OP_SEND, BBB)
+    L_SEND:
+    {
+      /* push nil after arguments */
+      int bidx = (c == CALL_MAXARGS) ? a+2 : a+c+1;
+      SET_NIL_VALUE(regs[bidx]);
+      goto L_SENDB;
+    };
+    L_SEND_SYM:
+    {
+      /* push nil after arguments */
+      int bidx = (c == CALL_MAXARGS) ? a+2 : a+c+1;
+      SET_NIL_VALUE(regs[bidx]);
+      goto L_SENDB_SYM;
     };
 
-  L_SEND:
-    CASE(OP_SEND) {
-      /* A B C  R(A) := call(R(A),Syms(B),R(A+1),...,R(A+C)) */
-      int a = GETARG_A(i);
-      int n = GETARG_C(i);
-      int argc = (n == CALL_MAXARGS) ? -1 : n;
-      int bidx = (argc < 0) ? a+2 : a+n+1;
+    CASE(OP_SENDB, BBB)
+    L_SENDB:
+    mid = syms[b];
+    L_SENDB_SYM:
+    {
+      int argc = (c == CALL_MAXARGS) ? -1 : c;
+      int bidx = (argc < 0) ? a+2 : a+c+1;
       mrb_method_t m;
-      struct RClass *c;
+      struct RClass *cls;
       mrb_callinfo *ci = mrb->c->ci;
       mrb_value recv, blk;
-      mrb_sym mid = syms[GETARG_B(i)];
 
-      mrb_assert(bidx < ci->nregs);
+      mrb_assert(bidx < irep->nregs);
 
       recv = regs[a];
-      if (GET_OPCODE(i) != OP_SENDB) {
-        SET_NIL_VALUE(regs[bidx]);
-        blk = regs[bidx];
-      }
-      else {
-        blk = regs[bidx];
-        if (!mrb_nil_p(blk) && mrb_type(blk) != MRB_TT_PROC) {
-          blk = mrb_convert_type(mrb, blk, MRB_TT_PROC, "Proc", "to_proc");
-          /* The stack might have been reallocated during mrb_convert_type(),
-             see #3622 */
-          regs[bidx] = blk;
-        }
+      blk = regs[bidx];
+      if (!mrb_nil_p(blk) && mrb_type(blk) != MRB_TT_PROC) {
+        blk = mrb_convert_type(mrb, blk, MRB_TT_PROC, "Proc", "to_proc");
+        /* The stack might have been reallocated during mrb_convert_type(),
+           see #3622 */
+        regs[bidx] = blk;
       }
-      c = mrb_class(mrb, recv);
-      m = mrb_method_search_vm(mrb, &c, mid);
+      cls = mrb_class(mrb, recv);
+      m = mrb_method_search_vm(mrb, &cls, mid);
       if (MRB_METHOD_UNDEF_P(m)) {
         mrb_sym missing = mrb_intern_lit(mrb, "method_missing");
-        m = mrb_method_search_vm(mrb, &c, missing);
+        m = mrb_method_search_vm(mrb, &cls, missing);
         if (MRB_METHOD_UNDEF_P(m) || (missing == mrb->c->ci->mid && mrb_obj_eq(mrb, regs[0], recv))) {
-          mrb_value args = (argc < 0) ? regs[a+1] : mrb_ary_new_from_values(mrb, n, regs+a+1);
-          ERR_PC_SET(mrb, pc);
+          mrb_value args = (argc < 0) ? regs[a+1] : mrb_ary_new_from_values(mrb, c, regs+a+1);
+          ERR_PC_SET(mrb);
           mrb_method_missing(mrb, mid, recv, args);
         }
         if (argc >= 0) {
           if (a+2 >= irep->nregs) {
-            stack_extend(mrb, a+3);
+            mrb_stack_extend(mrb, a+3);
           }
-          regs[a+1] = mrb_ary_new_from_values(mrb, n, regs+a+1);
+          regs[a+1] = mrb_ary_new_from_values(mrb, c, regs+a+1);
           regs[a+2] = blk;
           argc = -1;
         }
@@ -1451,17 +1421,16 @@ RETRY_TRY_BLOCK:
       ci = cipush(mrb);
       ci->mid = mid;
       ci->stackent = mrb->c->stack;
-      ci->target_class = c;
+      ci->target_class = cls;
       ci->argc = argc;
 
-      ci->pc = pc + 1;
+      ci->pc = pc;
       ci->acc = a;
 
       /* prepare stack */
       mrb->c->stack += a;
 
       if (MRB_METHOD_CFUNC_P(m)) {
-        ci->nregs = (argc < 0) ? 3 : n+2;
         if (MRB_METHOD_PROC_P(m)) {
           struct RProc *p = MRB_METHOD_PROC(m);
 
@@ -1475,12 +1444,10 @@ RETRY_TRY_BLOCK:
         mrb_gc_arena_shrink(mrb, ai);
         if (mrb->exc) goto L_RAISE;
         ci = mrb->c->ci;
-        if (GET_OPCODE(i) == OP_SENDB) {
-          if (mrb_type(blk) == MRB_TT_PROC) {
-            struct RProc *p = mrb_proc_ptr(blk);
-            if (p && !MRB_PROC_STRICT_P(p) && MRB_PROC_ENV(p) == ci[-1].env) {
-              p->flags |= MRB_PROC_ORPHAN;
-            }
+        if (mrb_type(blk) == MRB_TT_PROC) {
+          struct RProc *p = mrb_proc_ptr(blk);
+          if (p && !MRB_PROC_STRICT_P(p) && MRB_PROC_ENV(p) == ci[-1].env) {
+            p->flags |= MRB_PROC_ORPHAN;
           }
         }
         if (!ci->target_class) { /* return from context modifying method (resume/yield) */
@@ -1509,21 +1476,13 @@ RETRY_TRY_BLOCK:
         irep = proc->body.irep;
         pool = irep->pool;
         syms = irep->syms;
-        ci->nregs = irep->nregs;
-        stack_extend(mrb, (argc < 0 && ci->nregs < 3) ? 3 : ci->nregs);
+        mrb_stack_extend(mrb, (argc < 0 && irep->nregs < 3) ? 3 : irep->nregs);
         pc = irep->iseq;
         JUMP;
       }
     }
 
-    CASE(OP_FSEND) {
-      /* A B C  R(A) := fcall(R(A),Syms(B),R(A+1),... ,R(A+C-1)) */
-      /* not implemented yet */
-      NEXT;
-    }
-
-    CASE(OP_CALL) {
-      /* A      R(A) := self.call(frame.argc, frame.argv) */
+    CASE(OP_CALL, Z) {
       mrb_callinfo *ci;
       mrb_value recv = mrb->c->stack[0];
       struct RProc *m = mrb_proc_ptr(recv);
@@ -1566,12 +1525,13 @@ RETRY_TRY_BLOCK:
         irep = m->body.irep;
         if (!irep) {
           mrb->c->stack[0] = mrb_nil_value();
-          goto L_RETURN;
+          a = 0;
+          c = OP_R_NORMAL;
+          goto L_OP_RETURN_BODY;
         }
         pool = irep->pool;
         syms = irep->syms;
-        ci->nregs = irep->nregs;
-        stack_extend(mrb, ci->nregs);
+        mrb_stack_extend(mrb, irep->nregs);
         if (ci->argc < 0) {
           if (irep->nregs > 3) {
             stack_clear(regs+3, irep->nregs-3);
@@ -1588,20 +1548,17 @@ RETRY_TRY_BLOCK:
       }
     }
 
-    CASE(OP_SUPER) {
-      /* A C  R(A) := super(R(A+1),... ,R(A+C+1)) */
-      int a = GETARG_A(i);
-      int n = GETARG_C(i);
-      int argc = (n == CALL_MAXARGS) ? -1 : n;
-      int bidx = (argc < 0) ? a+2 : a+n+1;
+    CASE(OP_SUPER, BB) {
+      int argc = (b == CALL_MAXARGS) ? -1 : b;
+      int bidx = (argc < 0) ? a+2 : a+b+1;
       mrb_method_t m;
-      struct RClass *c;
+      struct RClass *cls;
       mrb_callinfo *ci = mrb->c->ci;
       mrb_value recv, blk;
       mrb_sym mid = ci->mid;
       struct RClass* target_class = MRB_PROC_TARGET_CLASS(ci->proc);
 
-      mrb_assert(bidx < ci->nregs);
+      mrb_assert(bidx < irep->nregs);
 
       if (mid == 0 || !target_class) {
         mrb_value exc = mrb_exc_new_str_lit(mrb, E_NOMETHOD_ERROR, "super called outside of method");
@@ -1631,26 +1588,26 @@ RETRY_TRY_BLOCK:
         regs[bidx] = blk;
         ci = mrb->c->ci;
       }
-      c = target_class->super;
-      m = mrb_method_search_vm(mrb, &c, mid);
+      cls = target_class->super;
+      m = mrb_method_search_vm(mrb, &cls, mid);
       if (MRB_METHOD_UNDEF_P(m)) {
         mrb_sym missing = mrb_intern_lit(mrb, "method_missing");
 
         if (mid != missing) {
-          c = mrb_class(mrb, recv);
+          cls = mrb_class(mrb, recv);
         }
-        m = mrb_method_search_vm(mrb, &c, missing);
+        m = mrb_method_search_vm(mrb, &cls, missing);
         if (MRB_METHOD_UNDEF_P(m)) {
-          mrb_value args = (argc < 0) ? regs[a+1] : mrb_ary_new_from_values(mrb, n, regs+a+1);
-          ERR_PC_SET(mrb, pc);
+          mrb_value args = (argc < 0) ? regs[a+1] : mrb_ary_new_from_values(mrb, b, regs+a+1);
+          ERR_PC_SET(mrb);
           mrb_method_missing(mrb, mid, recv, args);
         }
         mid = missing;
         if (argc >= 0) {
-          if (a+2 >= ci->nregs) {
-            stack_extend(mrb, a+3);
+          if (a+2 >= irep->nregs) {
+            mrb_stack_extend(mrb, a+3);
           }
-          regs[a+1] = mrb_ary_new_from_values(mrb, n, regs+a+1);
+          regs[a+1] = mrb_ary_new_from_values(mrb, b, regs+a+1);
           regs[a+2] = blk;
           argc = -1;
         }
@@ -1661,8 +1618,8 @@ RETRY_TRY_BLOCK:
       ci = cipush(mrb);
       ci->mid = mid;
       ci->stackent = mrb->c->stack;
-      ci->target_class = c;
-      ci->pc = pc + 1;
+      ci->target_class = cls;
+      ci->pc = pc;
       ci->argc = argc;
 
       /* prepare stack */
@@ -1671,7 +1628,7 @@ RETRY_TRY_BLOCK:
 
       if (MRB_METHOD_CFUNC_P(m)) {
         mrb_value v;
-        ci->nregs = (argc < 0) ? 3 : n+2;
+
         if (MRB_METHOD_PROC_P(m)) {
           ci->proc = MRB_METHOD_PROC(m);
         }
@@ -1708,21 +1665,18 @@ RETRY_TRY_BLOCK:
         irep = proc->body.irep;
         pool = irep->pool;
         syms = irep->syms;
-        ci->nregs = irep->nregs;
-        stack_extend(mrb, (argc < 0 && ci->nregs < 3) ? 3 : ci->nregs);
+        mrb_stack_extend(mrb, (argc < 0 && irep->nregs < 3) ? 3 : irep->nregs);
         pc = irep->iseq;
         JUMP;
       }
     }
 
-    CASE(OP_ARGARY) {
-      /* A Bx   R(A) := argument array (16=6:1:5:4) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      int m1 = (bx>>10)&0x3f;
-      int r  = (bx>>9)&0x1;
-      int m2 = (bx>>4)&0x1f;
-      int lv = (bx>>0)&0xf;
+    CASE(OP_ARGARY, BS) {
+      int m1 = (b>>11)&0x3f;
+      int r  = (b>>10)&0x1;
+      int m2 = (b>>5)&0x1f;
+      int kd = (b>>4)&0x1;
+      int lv = (b>>0)&0xf;
       mrb_value *stack;
 
       if (mrb->c->ci->mid == 0 || mrb->c->ci->target_class == NULL) {
@@ -1737,12 +1691,12 @@ RETRY_TRY_BLOCK:
       else {
         struct REnv *e = uvenv(mrb, lv-1);
         if (!e) goto L_NOSUPER;
-        if (MRB_ENV_STACK_LEN(e) <= m1+r+m2+1)
+        if (MRB_ENV_STACK_LEN(e) <= m1+r+m2+kd+1)
           goto L_NOSUPER;
         stack = e->stack + 1;
       }
       if (r == 0) {
-        regs[a] = mrb_ary_new_from_values(mrb, m1+m2, stack);
+        regs[a] = mrb_ary_new_from_values(mrb, m1+m2+kd, stack);
       }
       else {
         mrb_value *pp = NULL;
@@ -1755,7 +1709,7 @@ RETRY_TRY_BLOCK:
           pp = ARY_PTR(ary);
           len = (int)ARY_LEN(ary);
         }
-        regs[a] = mrb_ary_new_capa(mrb, m1+len+m2);
+        regs[a] = mrb_ary_new_capa(mrb, m1+len+m2+kd);
         rest = mrb_ary_ptr(regs[a]);
         if (m1 > 0) {
           stack_copy(ARY_PTR(rest), stack, m1);
@@ -1766,89 +1720,126 @@ RETRY_TRY_BLOCK:
         if (m2 > 0) {
           stack_copy(ARY_PTR(rest)+m1+len, stack+m1+1, m2);
         }
-        ARY_SET_LEN(rest, m1+len+m2);
+        if (kd) {
+          stack_copy(ARY_PTR(rest)+m1+len+m2, stack+m1+m2+1, kd);
+        }
+        ARY_SET_LEN(rest, m1+len+m2+kd);
       }
       regs[a+1] = stack[m1+r+m2];
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
 
-    CASE(OP_ENTER) {
-      /* Ax             arg setup according to flags (23=5:5:1:5:5:1:1) */
-      /* number of optional arguments times OP_JMP should follow */
-      mrb_aspec ax = GETARG_Ax(i);
-      int m1 = MRB_ASPEC_REQ(ax);
-      int o  = MRB_ASPEC_OPT(ax);
-      int r  = MRB_ASPEC_REST(ax);
-      int m2 = MRB_ASPEC_POST(ax);
+    CASE(OP_ENTER, W) {
+      int m1 = MRB_ASPEC_REQ(a);
+      int o  = MRB_ASPEC_OPT(a);
+      int r  = MRB_ASPEC_REST(a);
+      int m2 = MRB_ASPEC_POST(a);
+      int kd = (MRB_ASPEC_KEY(a) > 0 || MRB_ASPEC_KDICT(a))? 1 : 0;
       /* unused
-      int k  = MRB_ASPEC_KEY(ax);
-      int kd = MRB_ASPEC_KDICT(ax);
-      int b  = MRB_ASPEC_BLOCK(ax);
+      int b  = MRB_ASPEC_BLOCK(a);
       */
       int argc = mrb->c->ci->argc;
       mrb_value *argv = regs+1;
-      mrb_value *argv0 = argv;
-      int len = m1 + o + r + m2;
+      mrb_value * const argv0 = argv;
+      int const len = m1 + o + r + m2;
+      int const blk_pos = len + kd + 1;
       mrb_value *blk = &argv[argc < 0 ? 1 : argc];
+      mrb_value kdict;
+      int kargs = kd;
 
+      /* arguments is passed with Array */
       if (argc < 0) {
         struct RArray *ary = mrb_ary_ptr(regs[1]);
         argv = ARY_PTR(ary);
         argc = (int)ARY_LEN(ary);
         mrb_gc_protect(mrb, regs[1]);
       }
+
+      /* strict argument check */
       if (mrb->c->ci->proc && MRB_PROC_STRICT_P(mrb->c->ci->proc)) {
-        if (argc >= 0) {
-          if (argc < m1 + m2 || (r == 0 && argc > len)) {
-            argnum_error(mrb, m1+m2);
-            goto L_RAISE;
-          }
+        if (argc < m1 + m2 || (r == 0 && argc > len + kd)) {
+          argnum_error(mrb, m1+m2);
+          goto L_RAISE;
         }
       }
+      /* extract first argument array to arguments */
       else if (len > 1 && argc == 1 && mrb_array_p(argv[0])) {
         mrb_gc_protect(mrb, argv[0]);
         argc = (int)RARRAY_LEN(argv[0]);
         argv = RARRAY_PTR(argv[0]);
       }
-      if (argc < len) {
+
+      if (kd) {
+        /* check last arguments is hash if method takes keyword arguments */
+        if (argc == m1+m2) {
+          kdict = mrb_hash_new(mrb);
+          kargs = 0;
+        }
+        else {
+          if (argv && argc > 0 && mrb_hash_p(argv[argc-1])) {
+            kdict = argv[argc-1];
+            mrb_hash_check_kdict(mrb, kdict);
+          }
+          else if (r || argc <= m1+m2+o
+                   || !(mrb->c->ci->proc && MRB_PROC_STRICT_P(mrb->c->ci->proc))) {
+            kdict = mrb_hash_new(mrb);
+            kargs = 0;
+          }
+          else {
+            argnum_error(mrb, m1+m2);
+            goto L_RAISE;
+          }
+          if (MRB_ASPEC_KEY(a) > 0) {
+            kdict = mrb_hash_dup(mrb, kdict);
+          }
+        }
+      }
+
+      /* no rest arguments */
+      if (argc-kargs < len) {
         int mlen = m2;
         if (argc < m1+m2) {
-          if (m1 < argc)
-            mlen = argc - m1;
-          else
-            mlen = 0;
+          mlen = m1 < argc ? argc - m1 : 0;
         }
-        regs[len+1] = *blk; /* move block */
-        SET_NIL_VALUE(regs[argc+1]);
+        regs[blk_pos] = *blk; /* move block */
+        if (kd) regs[len + 1] = kdict;
+
+        /* copy mandatory and optional arguments */
         if (argv0 != argv) {
           value_move(&regs[1], argv, argc-mlen); /* m1 + o */
         }
         if (argc < m1) {
           stack_clear(&regs[argc+1], m1-argc);
         }
+        /* copy post mandatory arguments */
         if (mlen) {
           value_move(&regs[len-m2+1], &argv[argc-mlen], mlen);
         }
         if (mlen < m2) {
           stack_clear(&regs[len-m2+mlen+1], m2-mlen);
         }
+        /* initalize rest arguments with empty Array */
         if (r) {
           regs[m1+o+1] = mrb_ary_new_capa(mrb, 0);
         }
-        if (o == 0 || argc < m1+m2) pc++;
-        else
-          pc += argc - m1 - m2 + 1;
+        /* skip initailizer of passed arguments */
+        if (o > 0 && argc-kargs > m1+m2)
+          pc += (argc - kargs - m1 - m2)*3;
       }
       else {
         int rnum = 0;
         if (argv0 != argv) {
-          regs[len+1] = *blk; /* move block */
+          regs[blk_pos] = *blk; /* move block */
+          if (kd) regs[len + 1] = kdict;
           value_move(&regs[1], argv, m1+o);
         }
         if (r) {
-          rnum = argc-m1-o-m2;
-          regs[m1+o+1] = mrb_ary_new_from_values(mrb, rnum, argv+m1+o);
+          mrb_value ary;
+
+          rnum = argc-m1-o-m2-kargs;
+          ary = mrb_ary_new_from_values(mrb, rnum, argv+m1+o);
+          regs[m1+o+1] = ary;
         }
         if (m2) {
           if (argc-m2 > m1) {
@@ -1856,36 +1847,74 @@ RETRY_TRY_BLOCK:
           }
         }
         if (argv0 == argv) {
-          regs[len+1] = *blk; /* move block */
+          regs[blk_pos] = *blk; /* move block */
+          if (kd) regs[len + 1] = kdict;
         }
-        pc += o + 1;
+        pc += o*3;
       }
-      mrb->c->ci->argc = len;
+
+      /* format arguments for generated code */
+      mrb->c->ci->argc = len + kd;
+
       /* clear local (but non-argument) variables */
-      if (irep->nlocals-len-2 > 0) {
-        stack_clear(&regs[len+2], irep->nlocals-len-2);
+      if (irep->nlocals-blk_pos-1 > 0) {
+        stack_clear(&regs[blk_pos+1], irep->nlocals-blk_pos-1);
       }
       JUMP;
     }
 
-    CASE(OP_KARG) {
-      /* A B C          R(A) := kdict[Syms(B)]; if C kdict.rm(Syms(B)) */
-      /* if C == 2; raise unless kdict.empty? */
-      /* OP_JMP should follow to skip init code */
+    CASE(OP_KARG, BB) {
+      mrb_value k = mrb_symbol_value(syms[b]);
+      mrb_value kdict = regs[mrb->c->ci->argc];
+
+      if (!mrb_hash_p(kdict) || !mrb_hash_key_p(mrb, kdict, k)) {
+        mrb_value str = mrb_format(mrb, "missing keyword: %S", k);
+        mrb_exc_set(mrb, mrb_exc_new_str(mrb, E_ARGUMENT_ERROR, str));
+        goto L_RAISE;
+      }
+      regs[a] = mrb_hash_get(mrb, kdict, k);
+      mrb_hash_delete_key(mrb, kdict, k);
       NEXT;
     }
 
-    CASE(OP_KDICT) {
-      /* A C            R(A) := kdict */
+    CASE(OP_KEY_P, BB) {
+      mrb_value k = mrb_symbol_value(syms[b]);
+      mrb_value kdict = regs[mrb->c->ci->argc];
+      mrb_bool key_p = FALSE;
+
+      if (mrb_hash_p(kdict)) {
+        key_p = mrb_hash_key_p(mrb, kdict, k);
+      }
+      regs[a] = mrb_bool_value(key_p);
       NEXT;
     }
 
+    CASE(OP_KEYEND, Z) {
+      mrb_value kdict = regs[mrb->c->ci->argc];
+
+      if (mrb_hash_p(kdict) && !mrb_hash_empty_p(mrb, kdict)) {
+        mrb_value keys = mrb_hash_keys(mrb, kdict);
+        mrb_value key1 = RARRAY_PTR(keys)[0];
+        mrb_value str = mrb_format(mrb, "unknown keyword: %S", key1);
+        mrb_exc_set(mrb, mrb_exc_new_str(mrb, E_ARGUMENT_ERROR, str));
+        goto L_RAISE;
+      }
+      NEXT;
+    }
+
+    CASE(OP_BREAK, B) {
+      c = OP_R_BREAK;
+      goto L_RETURN;
+    }
+    CASE(OP_RETURN_BLK, B) {
+      c = OP_R_RETURN;
+      goto L_RETURN;
+    }
+    CASE(OP_RETURN, B)
+    c = OP_R_NORMAL;
     L_RETURN:
-      i = MKOP_AB(OP_RETURN, GETARG_A(i), OP_R_NORMAL);
-      /* fall through */
-    CASE(OP_RETURN) {
-      /* A B     return R(A) (B=normal,in-block return/break) */
-      mrb_callinfo *ci;
+    {
+       mrb_callinfo *ci;
 
 #define ecall_adjust() do {\
   ptrdiff_t cioff = ci - mrb->c->cibase;\
@@ -1943,7 +1972,7 @@ RETRY_TRY_BLOCK:
                 while (c->eidx > ci->epos) {
                   ecall_adjust();
                 }
-                mrb->c->status = MRB_FIBER_TERMINATED;
+                c->status = MRB_FIBER_TERMINATED;
                 mrb->c = c->prev;
                 c->prev = NULL;
                 goto L_RAISE;
@@ -1967,8 +1996,8 @@ RETRY_TRY_BLOCK:
         if (ci < ci0) {
           mrb->c->stack = ci[1].stackent;
         }
-        stack_extend(mrb, irep->nregs);
-        pc = mrb->c->rescue[--ci->ridx];
+        mrb_stack_extend(mrb, irep->nregs);
+        pc = irep->iseq+mrb->c->rescue[--ci->ridx];
       }
       else {
         int acc;
@@ -1976,9 +2005,9 @@ RETRY_TRY_BLOCK:
         struct RProc *dst;
 
         ci = mrb->c->ci;
-        v = regs[GETARG_A(i)];
+        v = regs[a];
         mrb_gc_protect(mrb, v);
-        switch (GETARG_B(i)) {
+        switch (c) {
         case OP_R_RETURN:
           /* Fall through to OP_R_NORMAL otherwise */
           if (ci->acc >=0 && MRB_PROC_ENV_P(proc) && !MRB_PROC_STRICT_P(proc)) {
@@ -2010,22 +2039,21 @@ RETRY_TRY_BLOCK:
         case OP_R_NORMAL:
         NORMAL_RETURN:
           if (ci == mrb->c->cibase) {
-            struct mrb_context *c;
+            struct mrb_context *c = mrb->c;
 
-            if (!mrb->c->prev) { /* toplevel return */
-              localjump_error(mrb, LOCALJUMP_ERROR_RETURN);
-              goto L_RAISE;
+            if (!c->prev) { /* toplevel return */
+              regs[irep->nlocals] = v;
+              goto L_STOP;
             }
-            if (mrb->c->prev->ci == mrb->c->prev->cibase) {
+            if (c->prev->ci == c->prev->cibase) {
               mrb_value exc = mrb_exc_new_str_lit(mrb, E_FIBER_ERROR, "double resume");
               mrb_exc_set(mrb, exc);
               goto L_RAISE;
             }
-            while (mrb->c->eidx > 0) {
+            while (c->eidx > 0) {
               ecall(mrb);
             }
             /* automatic yield at the end */
-            c = mrb->c;
             c->status = MRB_FIBER_TERMINATED;
             mrb->c = c->prev;
             c->prev = NULL;
@@ -2035,7 +2063,7 @@ RETRY_TRY_BLOCK:
           break;
         case OP_R_BREAK:
           if (MRB_PROC_STRICT_P(proc)) goto NORMAL_RETURN;
-          if (MRB_PROC_ORPHAN_P(proc)) { 
+          if (MRB_PROC_ORPHAN_P(proc)) {
             mrb_value exc;
 
           L_BREAK_ERROR:
@@ -2133,91 +2161,12 @@ RETRY_TRY_BLOCK:
       JUMP;
     }
 
-    CASE(OP_TAILCALL) {
-      /* A B C  return call(R(A),Syms(B),R(A+1),... ,R(A+C+1)) */
-      int a = GETARG_A(i);
-      int b = GETARG_B(i);
-      int n = GETARG_C(i);
-      mrb_method_t m;
-      struct RClass *c;
-      mrb_callinfo *ci;
-      mrb_value recv;
-      mrb_sym mid = syms[b];
-
-      recv = regs[a];
-      c = mrb_class(mrb, recv);
-      m = mrb_method_search_vm(mrb, &c, mid);
-      if (MRB_METHOD_UNDEF_P(m)) {
-        mrb_value sym = mrb_symbol_value(mid);
-        mrb_sym missing = mrb_intern_lit(mrb, "method_missing");
-        m = mrb_method_search_vm(mrb, &c, missing);
-        if (MRB_METHOD_UNDEF_P(m)) {
-          mrb_value args;
-
-          if (n == CALL_MAXARGS) {
-            args = regs[a+1];
-          }
-          else {
-            args = mrb_ary_new_from_values(mrb, n, regs+a+1);
-          }
-          ERR_PC_SET(mrb, pc);
-          mrb_method_missing(mrb, mid, recv, args);
-        }
-        mid = missing;
-        if (n == CALL_MAXARGS) {
-          mrb_ary_unshift(mrb, regs[a+1], sym);
-        }
-        else {
-          value_move(regs+a+2, regs+a+1, ++n);
-          regs[a+1] = sym;
-        }
-      }
-
-      /* replace callinfo */
-      ci = mrb->c->ci;
-      ci->mid = mid;
-      ci->target_class = c;
-      if (n == CALL_MAXARGS) {
-        ci->argc = -1;
-      }
-      else {
-        ci->argc = n;
-      }
-
-      /* move stack */
-      value_move(mrb->c->stack, &regs[a], ci->argc+1);
-
-      if (MRB_METHOD_CFUNC_P(m)) {
-        mrb_value v = MRB_METHOD_CFUNC(m)(mrb, recv);
-        mrb->c->stack[0] = v;
-        mrb_gc_arena_restore(mrb, ai);
-        goto L_RETURN;
-      }
-      else {
-        /* setup environment for calling method */
-        struct RProc *p = MRB_METHOD_PROC(m);
-        irep = p->body.irep;
-        pool = irep->pool;
-        syms = irep->syms;
-        if (ci->argc < 0) {
-          stack_extend(mrb, (irep->nregs < 3) ? 3 : irep->nregs);
-        }
-        else {
-          stack_extend(mrb, irep->nregs);
-        }
-        pc = irep->iseq;
-      }
-      JUMP;
-    }
-
-    CASE(OP_BLKPUSH) {
-      /* A Bx   R(A) := block (16=6:1:5:4) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
-      int m1 = (bx>>10)&0x3f;
-      int r  = (bx>>9)&0x1;
-      int m2 = (bx>>4)&0x1f;
-      int lv = (bx>>0)&0xf;
+    CASE(OP_BLKPUSH, BS) {
+      int m1 = (b>>11)&0x3f;
+      int r  = (b>>10)&0x1;
+      int m2 = (b>>5)&0x1f;
+      int kd = (b>>4)&0x1;
+      int lv = (b>>0)&0xf;
       mrb_value *stack;
 
       if (lv == 0) stack = regs + 1;
@@ -2234,197 +2183,75 @@ RETRY_TRY_BLOCK:
         localjump_error(mrb, LOCALJUMP_ERROR_YIELD);
         goto L_RAISE;
       }
-      regs[a] = stack[m1+r+m2];
+      regs[a] = stack[m1+r+m2+kd];
       NEXT;
     }
 
 #define TYPES2(a,b) ((((uint16_t)(a))<<8)|(((uint16_t)(b))&0xff))
-#define OP_MATH_BODY(op,v1,v2) do {\
-  v1(regs[a]) = v1(regs[a]) op v2(regs[a+1]);\
-} while(0)
-
-    CASE(OP_ADD) {
-      /* A B C  R(A) := R(A)+R(A+1) (Syms[B]=:+,C=1)*/
-      int a = GETARG_A(i);
-
-      /* need to check if op is overridden */
-      switch (TYPES2(mrb_type(regs[a]),mrb_type(regs[a+1]))) {
-      case TYPES2(MRB_TT_FIXNUM,MRB_TT_FIXNUM):
-        {
-          mrb_int x, y, z;
-          mrb_value *regs_a = regs + a;
-
-          x = mrb_fixnum(regs_a[0]);
-          y = mrb_fixnum(regs_a[1]);
-          if (mrb_int_add_overflow(x, y, &z)) {
-#ifndef MRB_WITHOUT_FLOAT
-            SET_FLOAT_VALUE(mrb, regs_a[0], (mrb_float)x + (mrb_float)y);
-            break;
-#endif
-          }
-          SET_INT_VALUE(regs[a], z);
-        }
-        break;
-#ifndef MRB_WITHOUT_FLOAT
-      case TYPES2(MRB_TT_FIXNUM,MRB_TT_FLOAT):
-        {
-          mrb_int x = mrb_fixnum(regs[a]);
-          mrb_float y = mrb_float(regs[a+1]);
-          SET_FLOAT_VALUE(mrb, regs[a], (mrb_float)x + y);
-        }
-        break;
-      case TYPES2(MRB_TT_FLOAT,MRB_TT_FIXNUM):
-#ifdef MRB_WORD_BOXING
-        {
-          mrb_float x = mrb_float(regs[a]);
-          mrb_int y = mrb_fixnum(regs[a+1]);
-          SET_FLOAT_VALUE(mrb, regs[a], x + y);
-        }
-#else
-        OP_MATH_BODY(+,mrb_float,mrb_fixnum);
-#endif
-        break;
-      case TYPES2(MRB_TT_FLOAT,MRB_TT_FLOAT):
-#ifdef MRB_WORD_BOXING
-        {
-          mrb_float x = mrb_float(regs[a]);
-          mrb_float y = mrb_float(regs[a+1]);
-          SET_FLOAT_VALUE(mrb, regs[a], x + y);
-        }
+#define OP_MATH(op_name)                                                    \
+  /* need to check if op is overridden */                                   \
+  switch (TYPES2(mrb_type(regs[a]),mrb_type(regs[a+1]))) {                  \
+    OP_MATH_CASE_FIXNUM(op_name);                                           \
+    OP_MATH_CASE_FLOAT(op_name, fixnum, float);                             \
+    OP_MATH_CASE_FLOAT(op_name, float,  fixnum);                            \
+    OP_MATH_CASE_FLOAT(op_name, float,  float);                             \
+    OP_MATH_CASE_STRING_##op_name();                                        \
+    default:                                                                \
+      c = 1;                                                                \
+      mid = mrb_intern_lit(mrb, MRB_STRINGIZE(OP_MATH_OP_##op_name));       \
+      goto L_SEND_SYM;                                                      \
+  }                                                                         \
+  NEXT;
+#define OP_MATH_CASE_FIXNUM(op_name)                                        \
+  case TYPES2(MRB_TT_FIXNUM, MRB_TT_FIXNUM):                                \
+    {                                                                       \
+      mrb_int x = mrb_fixnum(regs[a]), y = mrb_fixnum(regs[a+1]), z;        \
+      if (mrb_int_##op_name##_overflow(x, y, &z))                           \
+        OP_MATH_OVERFLOW_INT(op_name, x, y, z);                             \
+      else                                                                  \
+        SET_INT_VALUE(regs[a], z);                                          \
+    }                                                                       \
+    break
+#ifdef MRB_WITHOUT_FLOAT
+#define OP_MATH_CASE_FLOAT(op_name, t1, t2) (void)0
+#define OP_MATH_OVERFLOW_INT(op_name, x, y, z) SET_INT_VALUE(regs[a], z)
 #else
-        OP_MATH_BODY(+,mrb_float,mrb_float);
+#define OP_MATH_CASE_FLOAT(op_name, t1, t2)                                     \
+  case TYPES2(OP_MATH_TT_##t1, OP_MATH_TT_##t2):                                \
+    {                                                                           \
+      mrb_float z = mrb_##t1(regs[a]) OP_MATH_OP_##op_name mrb_##t2(regs[a+1]); \
+      SET_FLOAT_VALUE(mrb, regs[a], z);                                         \
+    }                                                                           \
+    break
+#define OP_MATH_OVERFLOW_INT(op_name, x, y, z) \
+  SET_FLOAT_VALUE(mrb, regs[a], (mrb_float)x OP_MATH_OP_##op_name (mrb_float)y)
 #endif
-        break;
-#endif
-      case TYPES2(MRB_TT_STRING,MRB_TT_STRING):
-        regs[a] = mrb_str_plus(mrb, regs[a], regs[a+1]);
-        break;
-      default:
-        goto L_SEND;
-      }
-      mrb_gc_arena_restore(mrb, ai);
-      NEXT;
-    }
-
-    CASE(OP_SUB) {
-      /* A B C  R(A) := R(A)-R(A+1) (Syms[B]=:-,C=1)*/
-      int a = GETARG_A(i);
-
-      /* need to check if op is overridden */
-      switch (TYPES2(mrb_type(regs[a]),mrb_type(regs[a+1]))) {
-      case TYPES2(MRB_TT_FIXNUM,MRB_TT_FIXNUM):
-        {
-          mrb_int x, y, z;
+#define OP_MATH_CASE_STRING_add()                                           \
+  case TYPES2(MRB_TT_STRING, MRB_TT_STRING):                                \
+    regs[a] = mrb_str_plus(mrb, regs[a], regs[a+1]);                        \
+    mrb_gc_arena_restore(mrb, ai);                                          \
+    break
+#define OP_MATH_CASE_STRING_sub() (void)0
+#define OP_MATH_CASE_STRING_mul() (void)0
+#define OP_MATH_OP_add +
+#define OP_MATH_OP_sub -
+#define OP_MATH_OP_mul *
+#define OP_MATH_TT_fixnum MRB_TT_FIXNUM
+#define OP_MATH_TT_float  MRB_TT_FLOAT
 
-          x = mrb_fixnum(regs[a]);
-          y = mrb_fixnum(regs[a+1]);
-          if (mrb_int_sub_overflow(x, y, &z)) {
-#ifndef MRB_WITHOUT_FLOAT
-            SET_FLOAT_VALUE(mrb, regs[a], (mrb_float)x - (mrb_float)y);
-            break;
-#endif
-          }
-          SET_INT_VALUE(regs[a], z);
-        }
-        break;
-#ifndef MRB_WITHOUT_FLOAT
-      case TYPES2(MRB_TT_FIXNUM,MRB_TT_FLOAT):
-        {
-          mrb_int x = mrb_fixnum(regs[a]);
-          mrb_float y = mrb_float(regs[a+1]);
-          SET_FLOAT_VALUE(mrb, regs[a], (mrb_float)x - y);
-        }
-        break;
-      case TYPES2(MRB_TT_FLOAT,MRB_TT_FIXNUM):
-#ifdef MRB_WORD_BOXING
-        {
-          mrb_float x = mrb_float(regs[a]);
-          mrb_int y = mrb_fixnum(regs[a+1]);
-          SET_FLOAT_VALUE(mrb, regs[a], x - y);
-        }
-#else
-        OP_MATH_BODY(-,mrb_float,mrb_fixnum);
-#endif
-        break;
-      case TYPES2(MRB_TT_FLOAT,MRB_TT_FLOAT):
-#ifdef MRB_WORD_BOXING
-        {
-          mrb_float x = mrb_float(regs[a]);
-          mrb_float y = mrb_float(regs[a+1]);
-          SET_FLOAT_VALUE(mrb, regs[a], x - y);
-        }
-#else
-        OP_MATH_BODY(-,mrb_float,mrb_float);
-#endif
-        break;
-#endif
-      default:
-        goto L_SEND;
-      }
-      NEXT;
+    CASE(OP_ADD, B) {
+      OP_MATH(add);
     }
 
-    CASE(OP_MUL) {
-      /* A B C  R(A) := R(A)*R(A+1) (Syms[B]=:*,C=1)*/
-      int a = GETARG_A(i);
-
-      /* need to check if op is overridden */
-      switch (TYPES2(mrb_type(regs[a]),mrb_type(regs[a+1]))) {
-      case TYPES2(MRB_TT_FIXNUM,MRB_TT_FIXNUM):
-        {
-          mrb_int x, y, z;
+    CASE(OP_SUB, B) {
+      OP_MATH(sub);
+    }
 
-          x = mrb_fixnum(regs[a]);
-          y = mrb_fixnum(regs[a+1]);
-          if (mrb_int_mul_overflow(x, y, &z)) {
-#ifndef MRB_WITHOUT_FLOAT
-            SET_FLOAT_VALUE(mrb, regs[a], (mrb_float)x * (mrb_float)y);
-            break;
-#endif
-          }
-          SET_INT_VALUE(regs[a], z);
-        }
-        break;
-#ifndef MRB_WITHOUT_FLOAT
-      case TYPES2(MRB_TT_FIXNUM,MRB_TT_FLOAT):
-        {
-          mrb_int x = mrb_fixnum(regs[a]);
-          mrb_float y = mrb_float(regs[a+1]);
-          SET_FLOAT_VALUE(mrb, regs[a], (mrb_float)x * y);
-        }
-        break;
-      case TYPES2(MRB_TT_FLOAT,MRB_TT_FIXNUM):
-#ifdef MRB_WORD_BOXING
-        {
-          mrb_float x = mrb_float(regs[a]);
-          mrb_int y = mrb_fixnum(regs[a+1]);
-          SET_FLOAT_VALUE(mrb, regs[a], x * y);
-        }
-#else
-        OP_MATH_BODY(*,mrb_float,mrb_fixnum);
-#endif
-        break;
-      case TYPES2(MRB_TT_FLOAT,MRB_TT_FLOAT):
-#ifdef MRB_WORD_BOXING
-        {
-          mrb_float x = mrb_float(regs[a]);
-          mrb_float y = mrb_float(regs[a+1]);
-          SET_FLOAT_VALUE(mrb, regs[a], x * y);
-        }
-#else
-        OP_MATH_BODY(*,mrb_float,mrb_float);
-#endif
-        break;
-#endif
-      default:
-        goto L_SEND;
-      }
-      NEXT;
+    CASE(OP_MUL, B) {
+      OP_MATH(mul);
     }
 
-    CASE(OP_DIV) {
-      /* A B C  R(A) := R(A)/R(A+1) (Syms[B]=:/,C=1)*/
-      int a = GETARG_A(i);
+    CASE(OP_DIV, B) {
 #ifndef MRB_WITHOUT_FLOAT
       double x, y, f;
 #endif
@@ -2457,7 +2284,9 @@ RETRY_TRY_BLOCK:
         break;
 #endif
       default:
-        goto L_SEND;
+        c = 1;
+        mid = mrb_intern_lit(mrb, "/");
+        goto L_SEND_SYM;
       }
 
 #ifndef MRB_WITHOUT_FLOAT
@@ -2474,87 +2303,46 @@ RETRY_TRY_BLOCK:
       NEXT;
     }
 
-    CASE(OP_ADDI) {
-      /* A B C  R(A) := R(A)+C (Syms[B]=:+)*/
-      int a = GETARG_A(i);
-
-      /* need to check if + is overridden */
-      switch (mrb_type(regs[a])) {
-      case MRB_TT_FIXNUM:
-        {
-          mrb_int x = mrb_fixnum(regs[a]);
-          mrb_int y = GETARG_C(i);
-          mrb_int z;
-
-          if (mrb_int_add_overflow(x, y, &z)) {
-#ifndef MRB_WITHOUT_FLOAT
-            SET_FLOAT_VALUE(mrb, regs[a], (mrb_float)x + (mrb_float)y);
-            break;
-#endif
-          }
-          SET_INT_VALUE(regs[a], z);
-        }
-        break;
-#ifndef MRB_WITHOUT_FLOAT
-      case MRB_TT_FLOAT:
-#ifdef MRB_WORD_BOXING
-        {
-          mrb_float x = mrb_float(regs[a]);
-          SET_FLOAT_VALUE(mrb, regs[a], x + GETARG_C(i));
-        }
+#define OP_MATHI(op_name)                                                   \
+  /* need to check if op is overridden */                                   \
+  switch (mrb_type(regs[a])) {                                              \
+    OP_MATHI_CASE_FIXNUM(op_name);                                          \
+    OP_MATHI_CASE_FLOAT(op_name);                                           \
+    default:                                                                \
+      SET_INT_VALUE(regs[a+1], b);                                          \
+      c = 1;                                                                \
+      mid = mrb_intern_lit(mrb, MRB_STRINGIZE(OP_MATH_OP_##op_name));       \
+      goto L_SEND_SYM;                                                      \
+  }                                                                         \
+  NEXT;
+#define OP_MATHI_CASE_FIXNUM(op_name)                                       \
+  case MRB_TT_FIXNUM:                                                       \
+    {                                                                       \
+      mrb_int x = mrb_fixnum(regs[a]), y = (mrb_int)b, z;                   \
+      if (mrb_int_##op_name##_overflow(x, y, &z))                           \
+        OP_MATH_OVERFLOW_INT(op_name, x, y, z);                             \
+      else                                                                  \
+        SET_INT_VALUE(regs[a], z);                                          \
+    }                                                                       \
+    break
+#ifdef MRB_WITHOUT_FLOAT
+#define OP_MATHI_CASE_FLOAT(op_name) (void)0
 #else
-        mrb_float(regs[a]) += GETARG_C(i);
-#endif
-        break;
+#define OP_MATHI_CASE_FLOAT(op_name)                                        \
+  case MRB_TT_FLOAT:                                                        \
+    {                                                                       \
+      mrb_float z = mrb_float(regs[a]) OP_MATH_OP_##op_name b;              \
+      SET_FLOAT_VALUE(mrb, regs[a], z);                                     \
+    }                                                                       \
+    break
 #endif
-      default:
-        SET_INT_VALUE(regs[a+1], GETARG_C(i));
-        i = MKOP_ABC(OP_SEND, a, GETARG_B(i), 1);
-        goto L_SEND;
-      }
-      NEXT;
-    }
-
-    CASE(OP_SUBI) {
-      /* A B C  R(A) := R(A)-C (Syms[B]=:-)*/
-      int a = GETARG_A(i);
-      mrb_value *regs_a = regs + a;
 
-      /* need to check if + is overridden */
-      switch (mrb_type(regs_a[0])) {
-      case MRB_TT_FIXNUM:
-        {
-          mrb_int x = mrb_fixnum(regs_a[0]);
-          mrb_int y = GETARG_C(i);
-          mrb_int z;
+    CASE(OP_ADDI, BB) {
+      OP_MATHI(add);
+    }
 
-          if (mrb_int_sub_overflow(x, y, &z)) {
-#ifndef MRB_WITHOUT_FLOAT
-            SET_FLOAT_VALUE(mrb, regs_a[0], (mrb_float)x - (mrb_float)y);
-            break;
-#endif
-          }
-          SET_INT_VALUE(regs_a[0], z);
-        }
-        break;
-#ifndef MRB_WITHOUT_FLOAT
-      case MRB_TT_FLOAT:
-#ifdef MRB_WORD_BOXING
-        {
-          mrb_float x = mrb_float(regs[a]);
-          SET_FLOAT_VALUE(mrb, regs[a], x - GETARG_C(i));
-        }
-#else
-        mrb_float(regs_a[0]) -= GETARG_C(i);
-#endif
-        break;
-#endif
-      default:
-        SET_INT_VALUE(regs_a[1], GETARG_C(i));
-        i = MKOP_ABC(OP_SEND, a, GETARG_B(i), 1);
-        goto L_SEND;
-      }
-      NEXT;
+    CASE(OP_SUBI, BB) {
+      OP_MATHI(sub);
     }
 
 #define OP_CMP_BODY(op,v1,v2) (v1(regs[a]) op v2(regs[a+1]))
@@ -2568,7 +2356,9 @@ RETRY_TRY_BLOCK:
     result = OP_CMP_BODY(op,mrb_fixnum,mrb_fixnum);\
     break;\
   default:\
-    goto L_SEND;\
+    c = 1;\
+    mid = mrb_intern_lit(mrb, # op);\
+    goto L_SEND_SYM;\
   }\
   if (result) {\
     SET_TRUE_VALUE(regs[a]);\
@@ -2595,7 +2385,9 @@ RETRY_TRY_BLOCK:
     result = OP_CMP_BODY(op,mrb_float,mrb_float);\
     break;\
   default:\
-    goto L_SEND;\
+    c = 1;\
+    mid = mrb_intern_lit(mrb, # op);\
+    goto L_SEND_SYM;\
   }\
   if (result) {\
     SET_TRUE_VALUE(regs[a]);\
@@ -2606,9 +2398,7 @@ RETRY_TRY_BLOCK:
 } while(0)
 #endif
 
-    CASE(OP_EQ) {
-      /* A B C  R(A) := R(A)==R(A+1) (Syms[B]=:==,C=1)*/
-      int a = GETARG_A(i);
+    CASE(OP_EQ, B) {
       if (mrb_obj_eq(mrb, regs[a], regs[a+1])) {
         SET_TRUE_VALUE(regs[a]);
       }
@@ -2618,68 +2408,64 @@ RETRY_TRY_BLOCK:
       NEXT;
     }
 
-    CASE(OP_LT) {
-      /* A B C  R(A) := R(A)<R(A+1) (Syms[B]=:<,C=1)*/
-      int a = GETARG_A(i);
+    CASE(OP_LT, B) {
       OP_CMP(<);
       NEXT;
     }
 
-    CASE(OP_LE) {
-      /* A B C  R(A) := R(A)<=R(A+1) (Syms[B]=:<=,C=1)*/
-      int a = GETARG_A(i);
+    CASE(OP_LE, B) {
       OP_CMP(<=);
       NEXT;
     }
 
-    CASE(OP_GT) {
-      /* A B C  R(A) := R(A)>R(A+1) (Syms[B]=:>,C=1)*/
-      int a = GETARG_A(i);
+    CASE(OP_GT, B) {
       OP_CMP(>);
       NEXT;
     }
 
-    CASE(OP_GE) {
-      /* A B C  R(A) := R(A)>=R(A+1) (Syms[B]=:>=,C=1)*/
-      int a = GETARG_A(i);
+    CASE(OP_GE, B) {
       OP_CMP(>=);
       NEXT;
     }
 
-    CASE(OP_ARRAY) {
-      /* A B C          R(A) := ary_new(R(B),R(B+1)..R(B+C)) */
-      int a = GETARG_A(i);
-      int b = GETARG_B(i);
-      int c = GETARG_C(i);
+    CASE(OP_ARRAY, BB) {
+      mrb_value v = mrb_ary_new_from_values(mrb, b, &regs[a]);
+      regs[a] = v;
+      mrb_gc_arena_restore(mrb, ai);
+      NEXT;
+    }
+    CASE(OP_ARRAY2, BBB) {
       mrb_value v = mrb_ary_new_from_values(mrb, c, &regs[b]);
       regs[a] = v;
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
 
-    CASE(OP_ARYCAT) {
-      /* A B            mrb_ary_concat(R(A),R(B)) */
-      int a = GETARG_A(i);
-      int b = GETARG_B(i);
-      mrb_value splat = mrb_ary_splat(mrb, regs[b]);
+    CASE(OP_ARYCAT, B) {
+      mrb_value splat = mrb_ary_splat(mrb, regs[a+1]);
       mrb_ary_concat(mrb, regs[a], splat);
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
 
-    CASE(OP_ARYPUSH) {
-      /* A B            R(A).push(R(B)) */
-      int a = GETARG_A(i);
-      int b = GETARG_B(i);
-      mrb_ary_push(mrb, regs[a], regs[b]);
+    CASE(OP_ARYPUSH, B) {
+      mrb_ary_push(mrb, regs[a], regs[a+1]);
       NEXT;
     }
 
-    CASE(OP_AREF) {
-      /* A B C          R(A) := R(B)[C] */
-      int a = GETARG_A(i);
-      int b = GETARG_B(i);
-      int c = GETARG_C(i);
+    CASE(OP_ARYDUP, B) {
+      mrb_value ary = regs[a];
+      if (mrb_array_p(ary)) {
+        ary = mrb_ary_new_from_values(mrb, RARRAY_LEN(ary), RARRAY_PTR(ary));
+      }
+      else {
+        ary = mrb_ary_new_from_values(mrb, 1, &ary);
+      }
+      regs[a] = ary;
+      NEXT;
+    }
+
+    CASE(OP_AREF, BBB) {
       mrb_value v = regs[b];
 
       if (!mrb_array_p(v)) {
@@ -2697,21 +2483,15 @@ RETRY_TRY_BLOCK:
       NEXT;
     }
 
-    CASE(OP_ASET) {
-      /* A B C          R(B)[C] := R(A) */
-      int a = GETARG_A(i);
-      int b = GETARG_B(i);
-      int c = GETARG_C(i);
+    CASE(OP_ASET, BBB) {
       mrb_ary_set(mrb, regs[b], c, regs[a]);
       NEXT;
     }
 
-    CASE(OP_APOST) {
-      /* A B C  *R(A),R(A+1)..R(A+C) := R(A)[B..] */
-      int a = GETARG_A(i);
+    CASE(OP_APOST, BBB) {
       mrb_value v = regs[a];
-      int pre  = GETARG_B(i);
-      int post = GETARG_C(i);
+      int pre  = b;
+      int post = c;
       struct RArray *ary;
       int len, idx;
 
@@ -2742,48 +2522,65 @@ RETRY_TRY_BLOCK:
       NEXT;
     }
 
-    CASE(OP_STRING) {
-      /* A Bx           R(A) := str_new(Lit(Bx)) */
-      mrb_int a = GETARG_A(i);
-      mrb_int bx = GETARG_Bx(i);
-      mrb_value str = mrb_str_dup(mrb, pool[bx]);
+    CASE(OP_INTERN, B) {
+      mrb_sym sym = mrb_intern_str(mrb, regs[a]);
+
+      regs[a] = mrb_symbol_value(sym);
+      mrb_gc_arena_restore(mrb, ai);
+      NEXT;
+    }
+
+    CASE(OP_STRING, BB) {
+      mrb_value str = mrb_str_dup(mrb, pool[b]);
 
       regs[a] = str;
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
 
-    CASE(OP_STRCAT) {
-      /* A B    R(A).concat(R(B)) */
-      mrb_int a = GETARG_A(i);
-      mrb_int b = GETARG_B(i);
+    CASE(OP_STRCAT, B) {
+      mrb_str_concat(mrb, regs[a], regs[a+1]);
+      NEXT;
+    }
+
+    CASE(OP_HASH, BB) {
+      mrb_value hash = mrb_hash_new_capa(mrb, b);
+      int i;
+      int lim = a+b*2;
 
-      mrb_str_concat(mrb, regs[a], regs[b]);
+      for (i=a; i<lim; i+=2) {
+        mrb_hash_set(mrb, hash, regs[i], regs[i+1]);
+      }
+      regs[a] = hash;
+      mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
 
-    CASE(OP_HASH) {
-      /* A B C   R(A) := hash_new(R(B),R(B+1)..R(B+C)) */
-      int b = GETARG_B(i);
-      int c = GETARG_C(i);
-      int lim = b+c*2;
-      mrb_value hash = mrb_hash_new_capa(mrb, c);
+    CASE(OP_HASHADD, BB) {
+      mrb_value hash;
+      int i;
+      int lim = a+b*2+1;
 
-      while (b < lim) {
-        mrb_hash_set(mrb, hash, regs[b], regs[b+1]);
-        b+=2;
+      hash = mrb_ensure_hash_type(mrb, regs[a]);
+      for (i=a+1; i<lim; i+=2) {
+        mrb_hash_set(mrb, hash, regs[i], regs[i+1]);
       }
-      regs[GETARG_A(i)] = hash;
+      mrb_gc_arena_restore(mrb, ai);
+      NEXT;
+    }
+    CASE(OP_HASHCAT, B) {
+      mrb_value hash = mrb_ensure_hash_type(mrb, regs[a]);
+
+      mrb_hash_merge(mrb, hash, regs[a+1]);
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
 
-    CASE(OP_LAMBDA) {
-      /* A b c  R(A) := lambda(SEQ[b],c) (b:c = 14:2) */
+    CASE(OP_LAMBDA, BB)
+    c = OP_L_LAMBDA;
+    L_MAKE_LAMBDA:
+    {
       struct RProc *p;
-      int a = GETARG_A(i);
-      int b = GETARG_b(i);
-      int c = GETARG_c(i);
       mrb_irep *nirep = irep->reps[b];
 
       if (c & OP_L_CAPTURE) {
@@ -2798,19 +2595,38 @@ RETRY_TRY_BLOCK:
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
+    CASE(OP_BLOCK, BB) {
+      c = OP_L_BLOCK;
+      goto L_MAKE_LAMBDA;
+    }
+    CASE(OP_METHOD, BB) {
+      c = OP_L_METHOD;
+      goto L_MAKE_LAMBDA;
+    }
+
+    CASE(OP_RANGE_INC, B) {
+      mrb_value val = mrb_range_new(mrb, regs[a], regs[a+1], FALSE);
+      regs[a] = val;
+      mrb_gc_arena_restore(mrb, ai);
+      NEXT;
+    }
 
-    CASE(OP_OCLASS) {
-      /* A      R(A) := ::Object */
-      regs[GETARG_A(i)] = mrb_obj_value(mrb->object_class);
+    CASE(OP_RANGE_EXC, B) {
+      mrb_value val = mrb_range_new(mrb, regs[a], regs[a+1], TRUE);
+      regs[a] = val;
+      mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
 
-    CASE(OP_CLASS) {
-      /* A B    R(A) := newclass(R(A),Syms(B),R(A+1)) */
+    CASE(OP_OCLASS, B) {
+      regs[a] = mrb_obj_value(mrb->object_class);
+      NEXT;
+    }
+
+    CASE(OP_CLASS, BB) {
       struct RClass *c = 0, *baseclass;
-      int a = GETARG_A(i);
       mrb_value base, super;
-      mrb_sym id = syms[GETARG_B(i)];
+      mrb_sym id = syms[b];
 
       base = regs[a];
       super = regs[a+1];
@@ -2824,32 +2640,27 @@ RETRY_TRY_BLOCK:
       NEXT;
     }
 
-    CASE(OP_MODULE) {
-      /* A B            R(A) := newmodule(R(A),Syms(B)) */
-      struct RClass *c = 0, *baseclass;
-      int a = GETARG_A(i);
+    CASE(OP_MODULE, BB) {
+      struct RClass *cls = 0, *baseclass;
       mrb_value base;
-      mrb_sym id = syms[GETARG_B(i)];
+      mrb_sym id = syms[b];
 
       base = regs[a];
       if (mrb_nil_p(base)) {
         baseclass = MRB_PROC_TARGET_CLASS(mrb->c->ci->proc);
         base = mrb_obj_value(baseclass);
       }
-      c = mrb_vm_define_module(mrb, base, id);
-      regs[a] = mrb_obj_value(c);
+      cls = mrb_vm_define_module(mrb, base, id);
+      regs[a] = mrb_obj_value(cls);
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
 
-    CASE(OP_EXEC) {
-      /* A Bx   R(A) := blockexec(R(A),SEQ[Bx]) */
-      int a = GETARG_A(i);
-      int bx = GETARG_Bx(i);
+    CASE(OP_EXEC, BB) {
       mrb_callinfo *ci;
       mrb_value recv = regs[a];
       struct RProc *p;
-      mrb_irep *nirep = irep->reps[bx];
+      mrb_irep *nirep = irep->reps[b];
 
       /* prepare closure */
       p = mrb_proc_new(mrb, nirep);
@@ -2860,7 +2671,7 @@ RETRY_TRY_BLOCK:
 
       /* prepare call stack */
       ci = cipush(mrb);
-      ci->pc = pc + 1;
+      ci->pc = pc;
       ci->acc = a;
       ci->mid = 0;
       ci->stackent = mrb->c->stack;
@@ -2876,63 +2687,59 @@ RETRY_TRY_BLOCK:
       irep = p->body.irep;
       pool = irep->pool;
       syms = irep->syms;
-      ci->nregs = irep->nregs;
-      stack_extend(mrb, ci->nregs);
-      stack_clear(regs+1, ci->nregs-1);
+      mrb_stack_extend(mrb, irep->nregs);
+      stack_clear(regs+1, irep->nregs-1);
       pc = irep->iseq;
       JUMP;
     }
 
-    CASE(OP_METHOD) {
-      /* A B            R(A).newmethod(Syms(B),R(A+1)) */
-      int a = GETARG_A(i);
-      struct RClass *c = mrb_class_ptr(regs[a]);
+    CASE(OP_DEF, BB) {
+      struct RClass *target = mrb_class_ptr(regs[a]);
       struct RProc *p = mrb_proc_ptr(regs[a+1]);
       mrb_method_t m;
 
       MRB_METHOD_FROM_PROC(m, p);
-      mrb_define_method_raw(mrb, c, syms[GETARG_B(i)], m);
+      mrb_define_method_raw(mrb, target, syms[b], m);
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
 
-    CASE(OP_SCLASS) {
-      /* A B    R(A) := R(B).singleton_class */
-      int a = GETARG_A(i);
-      int b = GETARG_B(i);
-
-      regs[a] = mrb_singleton_class(mrb, regs[b]);
+    CASE(OP_SCLASS, B) {
+      regs[a] = mrb_singleton_class(mrb, regs[a]);
       mrb_gc_arena_restore(mrb, ai);
       NEXT;
     }
 
-    CASE(OP_TCLASS) {
-      /* A      R(A) := target_class */
-      if (!mrb->c->ci->target_class) {
-        mrb_value exc = mrb_exc_new_str_lit(mrb, E_TYPE_ERROR, "no target class or module");
-        mrb_exc_set(mrb, exc);
-        goto L_RAISE;
-      }
-      regs[GETARG_A(i)] = mrb_obj_value(mrb->c->ci->target_class);
+    CASE(OP_TCLASS, B) {
+      if (!check_target_class(mrb)) goto L_RAISE;
+      regs[a] = mrb_obj_value(mrb->c->ci->target_class);
       NEXT;
     }
 
-    CASE(OP_RANGE) {
-      /* A B C  R(A) := range_new(R(B),R(B+1),C) */
-      int b = GETARG_B(i);
-      mrb_value val = mrb_range_new(mrb, regs[b], regs[b+1], GETARG_C(i));
-      regs[GETARG_A(i)] = val;
-      mrb_gc_arena_restore(mrb, ai);
+    CASE(OP_ALIAS, BB) {
+      struct RClass *target;
+
+      if (!check_target_class(mrb)) goto L_RAISE;
+      target = mrb->c->ci->target_class;
+      mrb_alias_method(mrb, target, syms[a], syms[b]);
+      NEXT;
+    }
+    CASE(OP_UNDEF, B) {
+      struct RClass *target;
+
+      if (!check_target_class(mrb)) goto L_RAISE;
+      target = mrb->c->ci->target_class;
+      mrb_undef_method_id(mrb, target, syms[a]);
       NEXT;
     }
 
-    CASE(OP_DEBUG) {
-      /* A B C    debug print R(A),R(B),R(C) */
+    CASE(OP_DEBUG, Z) {
+      FETCH_BBB();
 #ifdef MRB_ENABLE_DEBUG_HOOK
       mrb->debug_op_hook(mrb, irep, pc, regs);
 #else
 #ifndef MRB_DISABLE_STDIO
-      printf("OP_DEBUG %d %d %d\n", GETARG_A(i), GETARG_B(i), GETARG_C(i));
+      printf("OP_DEBUG %d %d %d\n", a, b, c);
 #else
       abort();
 #endif
@@ -2940,12 +2747,54 @@ RETRY_TRY_BLOCK:
       NEXT;
     }
 
-    CASE(OP_STOP) {
+    CASE(OP_ERR, B) {
+      mrb_value msg = mrb_str_dup(mrb, pool[a]);
+      mrb_value exc;
+
+      exc = mrb_exc_new_str(mrb, E_LOCALJUMP_ERROR, msg);
+      ERR_PC_SET(mrb);
+      mrb_exc_set(mrb, exc);
+      goto L_RAISE;
+    }
+
+    CASE(OP_EXT1, Z) {
+      insn = READ_B();
+      switch (insn) {
+#define OPCODE(insn,ops) case OP_ ## insn: FETCH_ ## ops ## _1(); goto L_OP_ ## insn ## _BODY;
+#include "mruby/ops.h"
+#undef OPCODE
+      }
+      pc--;
+      NEXT;
+    }
+    CASE(OP_EXT2, Z) {
+      insn = READ_B();
+      switch (insn) {
+#define OPCODE(insn,ops) case OP_ ## insn: FETCH_ ## ops ## _2(); goto L_OP_ ## insn ## _BODY;
+#include "mruby/ops.h"
+#undef OPCODE
+      }
+      pc--;
+      NEXT;
+    }
+    CASE(OP_EXT3, Z) {
+      uint8_t insn = READ_B();
+      switch (insn) {
+#define OPCODE(insn,ops) case OP_ ## insn: FETCH_ ## ops ## _3(); goto L_OP_ ## insn ## _BODY;
+#include "mruby/ops.h"
+#undef OPCODE
+      }
+      pc--;
+      NEXT;
+    }
+
+    CASE(OP_STOP, Z) {
       /*        stop VM */
     L_STOP:
       while (mrb->c->eidx > 0) {
         ecall(mrb);
       }
+      mrb->c->cibase->ridx = 0;
       ERR_PC_CLR(mrb);
       mrb->jmp = prev_jmp;
       if (mrb->exc) {
@@ -2953,26 +2802,9 @@ RETRY_TRY_BLOCK:
       }
       return regs[irep->nlocals];
     }
-
-    CASE(OP_ERR) {
-      /* Bx     raise RuntimeError with message Lit(Bx) */
-      mrb_value msg = mrb_str_dup(mrb, pool[GETARG_Bx(i)]);
-      mrb_value exc;
-
-      if (GETARG_A(i) == 0) {
-        exc = mrb_exc_new_str(mrb, E_RUNTIME_ERROR, msg);
-      }
-      else {
-        exc = mrb_exc_new_str(mrb, E_LOCALJUMP_ERROR, msg);
-      }
-      ERR_PC_SET(mrb, pc);
-      mrb_exc_set(mrb, exc);
-      goto L_RAISE;
-    }
   }
   END_DISPATCH;
 #undef regs
-
   }
   MRB_CATCH(&c_jmp) {
     exc_catched = TRUE;
@@ -3005,12 +2837,11 @@ mrb_top_run(mrb_state *mrb, struct RProc *proc, mrb_value self, unsigned int sta
     return mrb_vm_run(mrb, proc, self, stack_keep);
   }
   ci = cipush(mrb);
+  ci->stackent = mrb->c->stack;
   ci->mid = 0;
-  ci->nregs = 1;   /* protect the receiver */
   ci->acc = CI_ACC_SKIP;
   ci->target_class = mrb->object_class;
   v = mrb_vm_run(mrb, proc, self, stack_keep);
-  cipop(mrb);
 
   return v;
 }