math.c: check argument to tgamma

* math.c (math_gamma): check the argument before calling math
  function `tgamma` for edge cases.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58697 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 7 insertions, 1 deletions

diff --git a/math.c b/math.c
index 570776baef..6a55966c49 100644
--- a/math.c
+++ b/math.c
@@ -869,7 +869,13 @@ math_gamma(VALUE unused_obj, VALUE x)
     double d;
     d = Get_Double(x);
     /* check for domain error */
-    if (isinf(d) && signbit(d)) domain_error("gamma");
+    if (isinf(d)) {
+	if (signbit(d)) domain_error("gamma");
+	return DBL2NUM(INFINITY);
+    }
+    if (d == 0.0) {
+	return signbit(d) ? DBL2NUM(-INFINITY) : DBL2NUM(INFINITY);
+    }
     if (d == floor(d)) {
 	if (d < 0.0) domain_error("gamma");
 	if (1.0 <= d && d <= (double)NFACT_TABLE) {