simply use `isfinite`

include/mruby/value.h

@@ -60,6 +60,7 @@ typedef short mrb_sym;
 # define snprintf _snprintf
 # if _MSC_VER < 1800
 #  include <float.h>
+#  define isfinite(n) _finite(n)
 #  define isnan _isnan
 #  define isinf(n) (!_finite(n) && !_isnan(n))
 #  define signbit(n) (_copysign(1.0, (n)) < 0.0)

mrbgems/mruby-sprintf/src/sprintf.c

@@ -999,7 +999,7 @@ retry:
         char fbuf[32];
 
         fval = mrb_float(mrb_Float(mrb, val));
-        if (isnan(fval) || isinf(fval)) {
+        if (!isfinite(fval)) {
           const char *expr;
           const int elen = 3;
 

src/numeric.c

@@ -309,7 +309,7 @@ flodivmod(mrb_state *mrb, mrb_float x, mrb_float y, mrb_float *divp, mrb_float *
   }
   else {
     mod = fmod(x, y);
-    if (isinf(x) && !isinf(y) && !isnan(y))
+    if (isinf(x) && isfinite(y))
       div = x;
     else
       div = (x - mod) / y;
@@ -495,7 +495,7 @@ flo_finite_p(mrb_state *mrb, mrb_value num)
 {
   mrb_float value = mrb_float(num);
 
-  return mrb_bool_value(!(isinf(value) || isnan(value)));
+  return mrb_bool_value(isfinite(value));
 }
 
 /* 15.2.9.3.10 */
@@ -626,7 +626,7 @@ flo_round(mrb_state *mrb, mrb_value num)
   }
 
   if (ndigits > 0) {
-    if (isinf(number) || isnan(number)) return num;
+    if (!isfinite(number)) return num;
     return mrb_float_value(mrb, number);
   }
   return mrb_fixnum_value((mrb_int)number);