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

3 files changed, 19 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 51f506c778..802a124bfb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Apr  6 00:52:00 2016  Nobuyoshi Nakada  <[email protected]>
+
+	* math.c (ruby_tgamma): fix tgamma(-0.0) on mingw.
+	  [ruby-core:74817] [Bug #12249]
+
 Tue Apr  5 14:50:28 2016  NARUSE, Yui  <[email protected]>
 
 	* ext/nkf/nkf-utf8/nkf.c (mime_putc): fix typo.
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
 
 /*
diff --git a/test/ruby/test_math.rb b/test/ruby/test_math.rb
index e547cb77ec..c17b21a53d 100644
--- a/test/ruby/test_math.rb
+++ b/test/ruby/test_math.rb
@@ -255,6 +255,10 @@ class TestMath < Test::Unit::TestCase
     end
 
     assert_raise(Math::DomainError) { Math.gamma(-Float::INFINITY) }
+    x = Math.gamma(-0.0)
+    mesg = "Math.gamma(-0.0) should be -INF"
+    assert_infinity(x, mesg)
+    assert_predicate(x, :negative?, mesg)
   end
 
   def test_lgamma