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diff --git a/libgo/go/math/asin.go b/libgo/go/math/asin.go
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+++ b/libgo/go/math/asin.go
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+// Copyright 2009 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
+
+
+/*
+	Floating-point arcsine and arccosine.
+
+	They are implemented by computing the arctangent
+	after appropriate range reduction.
+*/
+
+// Asin returns the arcsine of x.
+//
+// Special cases are:
+//	Asin(±0) = ±0
+//	Asin(x) = NaN if x < -1 or x > 1
+func Asin(x float64) float64 {
+	if x == 0 {
+		return x // special case
+	}
+	sign := false
+	if x < 0 {
+		x = -x
+		sign = true
+	}
+	if x > 1 {
+		return NaN() // special case
+	}
+
+	temp := Sqrt(1 - x*x)
+	if x > 0.7 {
+		temp = Pi/2 - satan(temp/x)
+	} else {
+		temp = satan(x / temp)
+	}
+
+	if sign {
+		temp = -temp
+	}
+	return temp
+}
+
+// Acos returns the arccosine of x.
+//
+// Special case is:
+//	Acos(x) = NaN if x < -1 or x > 1
+func Acos(x float64) float64 { return Pi/2 - Asin(x) }