math.c: fix tgamma

* math.c (ruby_tgamma): fix tgamma(-0.0) on mingw.
  [ruby-core:74817] [Bug #12249]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@54492 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 10 insertions, 4 deletions

diff --git a/math.c b/math.c
index 591d6ae2f2..e1dfe975d2 100644
--- a/math.c
+++ b/math.c
@@ -734,14 +734,20 @@ math_erfc(VALUE obj, VALUE x)
     return DBL2NUM(erfc(Get_Double(x)));
 }
 
-#ifdef __MINGW32__
+#if defined __MINGW32__
 static inline double
-mingw_tgamma(const double d)
+ruby_tgamma(const double d)
 {
     const double g = tgamma(d);
-    return (isnan(g) && !signbit(d)) ? INFINITY : g;
+    if (isinf(g)) {
+	if (d == 0.0 && signbit(d)) return -INFINITY;
+    }
+    if (isnan(g)) {
+	if (!signbit(d)) return INFINITY;
+    }
+    return g;
 }
-#define tgamma(d) mingw_tgamma(d)
+#define tgamma(d) ruby_tgamma(d)
 #endif
 
 /*