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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)
}