Fix dump/load float leteral evaluate to infinity

Example:

  # example.rb
  p(2e308)
  p(-2e308)

  Good:

    $ bin/mruby example.rb
    inf
    -inf

  Bad:

    $ bin/mrbc example.rb
    $ bin/mruby -b example.mrb
    0
    -0

Cause:

  Float infinity representation is `inf` on dump and it is converted by
  corresponding `String#to_f` on load.

Treatment:

  - Introduce new representations (`i`: +infinity, `I`: -infinity)
  - Allow old representations (`inf`, `-inf`, `infinity`, `-infinity`) too
  - Raise error for unknown representations (use corresponding `Kernel#Float`)

2 files changed, 34 insertions, 3 deletions

diff --git a/src/dump.c b/src/dump.c
index 6ce9c4eb9..11eba4e40 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>
@@ -90,6 +91,18 @@ write_iseq_block(mrb_state *mrb, mrb_irep *irep, uint8_t *buf, uint8_t flags)
   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)
@@ -116,7 +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);
@@ -165,7 +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
 
diff --git a/src/load.c b/src/load.c
index 559fff1d4..55e0845f3 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)
 {
@@ -125,7 +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