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

ChangeLog

@@ -1,3 +1,8 @@
+Wed Apr  6 00:52:00 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* math.c (ruby_tgamma): fix tgamma(-0.0) on mingw.
+	  [ruby-core:74817] [Bug #12249]
+
 Tue Apr  5 14:50:28 2016  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* ext/nkf/nkf-utf8/nkf.c (mime_putc): fix typo.

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
 
 /*

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