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-rw-r--r--src/math/copysign.go12
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diff --git a/src/math/copysign.go b/src/math/copysign.go
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+// 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
+
+// Copysign returns a value with the magnitude
+// of x and the sign of y.
+func Copysign(x, y float64) float64 {
+ const sign = 1 << 63
+ return Float64frombits(Float64bits(x)&^sign | Float64bits(y)&sign)
+}