fix tgamma for inifity

* configure.in: do not use buggy tgamma() of mingw.

* missing/tgamma.c (tgamma): merge fix for inifity from
  ruby_tgamma.  since msvcr120.dll and later have tgamma, this
  implementation will not be used.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58691 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 21 insertions, 0 deletions

diff --git a/missing/tgamma.c b/missing/tgamma.c
index 9324e19ea1..6260e4f519 100644
--- a/missing/tgamma.c
+++ b/missing/tgamma.c
@@ -10,9 +10,25 @@ reference - Haruhiko Okumura: C-gengo niyoru saishin algorithm jiten
     gamma.c -- Gamma function
 ***********************************************************/
 #include "ruby/config.h"
+#include "ruby/missing.h"
 #include <math.h>
 #include <errno.h>
 
+#ifdef _WIN32
+# include <float.h>
+# if !defined __MINGW32__ || defined __NO_ISOCEXT
+#  ifndef isnan
+#   define isnan(x) _isnan(x)
+#  endif
+#  ifndef isinf
+#   define isinf(x) (!_finite(x) && !_isnan(x))
+#  endif
+#  ifndef finite
+#   define finite(x) _finite(x)
+#  endif
+# endif
+#endif
+
 #ifndef HAVE_LGAMMA_R
 
 #include <errno.h>
@@ -54,11 +70,16 @@ double tgamma(double x)  /* Gamma function */
         errno = ERANGE;
         return 1/x < 0 ? -HUGE_VAL : HUGE_VAL;
     }
+    if (isinf(x)) {
+        if (x < 0) goto domain_error;
+        return x;
+    }
     if (x < 0) {
         static double zero = 0.0;
         double i, f;
         f = modf(-x, &i);
         if (f == 0.0) { /* Domain Error */
+          domain_error:
             errno = EDOM;
             return zero/zero;
         }