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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

//extern asin

func libc_asin(float64) float64

func Asin(x float64) float64 {

        return libc_asin(x)

}

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

//extern acos

func libc_acos(float64) float64

func Acos(x float64) float64 {

        return libc_acos(x)

}

func acos(x float64) float64 {

        return Pi/2 - Asin(x)

}