numeric.c: introduce `mrb_int_to_cstr()` to dump `mrb_int`.

* refactor `mrb_integer_to_str()`
* refactor `mrb_str_format()`

1 files changed, 35 insertions, 19 deletions

diff --git a/src/numeric.c b/src/numeric.c
index fe9995bd4..a344440f4 100644
--- a/src/numeric.c
+++ b/src/numeric.c
@@ -1507,35 +1507,51 @@ int_sub(mrb_state *mrb, mrb_value self)
   return int_minus(mrb, self, other);
 }
 
-
-MRB_API mrb_value
-mrb_integer_to_str(mrb_state *mrb, mrb_value x, mrb_int base)
+MRB_API char*
+mrb_int_to_cstr(char *buf, size_t len, mrb_int n, mrb_int base)
 {
-  char buf[MRB_INT_BIT+1];
-  char *b = buf + sizeof buf;
-  mrb_int val = mrb_integer(x);
-  mrb_value str;
+  char *bufend = buf + len;
+  char *b = bufend-1;
 
-  if (base < 2 || 36 < base) {
-    mrb_raisef(mrb, E_ARGUMENT_ERROR, "invalid radix %i", base);
-  }
+  if (base < 2 || 36 < base) return NULL;
+  if (len < 2) return NULL;
 
-  if (val == 0) {
-    *--b = '0';
+  if (n == 0) {
+    buf[0] = '0';
+    buf[1] = '\0';
+    return buf;
   }
-  else if (val < 0) {
+
+  *b-- = '\0';
+  if (n < 0) {
     do {
-      *--b = mrb_digitmap[-(val % base)];
-    } while (val /= base);
-    *--b = '-';
+      if (b-- == buf) return NULL;
+      *b = mrb_digitmap[-(n % base)];
+    } while (n /= base);
+    if (b-- == buf) return NULL;
+    *b = '-';
   }
   else {
     do {
-      *--b = mrb_digitmap[(int)(val % base)];
-    } while (val /= base);
+      if (b-- == buf) return NULL;
+      *b = mrb_digitmap[(int)(n % base)];
+    } while (n /= base);
   }
+  return b;
+}
+
+MRB_API mrb_value
+mrb_integer_to_str(mrb_state *mrb, mrb_value x, mrb_int base)
+{
+  char buf[MRB_INT_BIT+1];
+  mrb_int val = mrb_integer(x);
 
-  str = mrb_str_new(mrb, b, buf + sizeof(buf) - b);
+  if (base < 2 || 36 < base) {
+    mrb_raisef(mrb, E_ARGUMENT_ERROR, "invalid radix %i", base);
+  }
+  const char *p = mrb_int_to_cstr(buf, sizeof(buf), val, base);
+  mrb_assert(p != NULL);
+  mrb_value str = mrb_str_new_cstr(mrb, p);
   RSTR_SET_ASCII_FLAG(mrb_str_ptr(str));
   return str;
 }