* 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

3 files changed, 18 insertions, 2 deletions

diff --git a/ChangeLog b/ChangeLog
index fa47ae5882..88f0372014 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Fri Aug 27 12:47:44 2010  Kenta Murata  <mrkn@mrkn.jp>
+
+	* 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.
+
 Fri Aug 27 12:26:23 2010  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* object.c (rb_obj_class): remove mention of obsolete method.
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));
 }
diff --git a/test/ruby/test_math.rb b/test/ruby/test_math.rb
index 64b72ce5c0..3895eec7f5 100644
--- a/test/ruby/test_math.rb
+++ b/test/ruby/test_math.rb
@@ -17,7 +17,10 @@ class TestMath < Test::Unit::TestCase
   end
 
   def test_atan2
-    assert_raise(Math::DomainError) { Math.atan2(0, 0) }
+    check(+0.0, Math.atan2(+0.0, +0.0))
+    check(-0.0, Math.atan2(-0.0, +0.0))
+    check(+Math::PI, Math.atan2(+0.0, -0.0))
+    check(-Math::PI, Math.atan2(-0.0, -0.0))
     assert_raise(Math::DomainError) { Math.atan2(Float::INFINITY, Float::INFINITY) }
     assert_raise(Math::DomainError) { Math.atan2(Float::INFINITY, -Float::INFINITY) }
     assert_raise(Math::DomainError) { Math.atan2(-Float::INFINITY, Float::INFINITY) }