* math.c (math_atan2): change the behavior when x and y are zero.

* test/ruby/test_math.rb (test_atan2): add tests for the above
  changes.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@29115 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 7 insertions, 1 deletions

diff --git a/math.c b/math.c
index 23bca55c4b..5461763d56 100644
--- a/math.c
+++ b/math.c
@@ -55,7 +55,13 @@ math_atan2(VALUE obj, VALUE y, VALUE x)
     Need_Float2(y, x);
     dx = RFLOAT_VALUE(x);
     dy = RFLOAT_VALUE(y);
-    if (dx == 0.0 && dy == 0.0) domain_error("atan2");
+    if (dx == 0.0 && dy == 0.0) {
+	if (!signbit(dx))
+	    return DBL2NUM(dy);
+        if (!signbit(dy))
+	    return DBL2NUM(M_PI);
+	return DBL2NUM(-M_PI);
+    }
     if (isinf(dx) && isinf(dy)) domain_error("atan2");
     return DBL2NUM(atan2(dy, dx));
 }