math: atan2 special cases (negative zero)

Added Signbit(), revised Copysign()

R=rsc
CC=golang-dev
http://codereview.appspot.com/822045

Committer: Russ Cox <rsc@golang.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/pkg/math/signbit.go b/src/pkg/math/signbit.go
new file mode 100644
index 000000000..670cc1a66
--- /dev/null
+++ b/src/pkg/math/signbit.go
@@ -0,0 +1,10 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package math
+
+// Signbit returns true if x is negative or negative zero.
+func Signbit(x float64) bool {
+	return Float64bits(x)&(1<<63) != 0
+}