github.com/twelsh-aw/go/src@v0.0.0-20230516233729-a56fe86a7c81/math/asin.go (about)

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package math
     6  
     7  /*
     8  	Floating-point arcsine and arccosine.
     9  
    10  	They are implemented by computing the arctangent
    11  	after appropriate range reduction.
    12  */
    13  
    14  // Asin returns the arcsine, in radians, of x.
    15  //
    16  // Special cases are:
    17  //
    18  //	Asin(±0) = ±0
    19  //	Asin(x) = NaN if x < -1 or x > 1
    20  func Asin(x float64) float64 {
    21  	if haveArchAsin {
    22  		return archAsin(x)
    23  	}
    24  	return asin(x)
    25  }
    26  
    27  func asin(x float64) float64 {
    28  	if x == 0 {
    29  		return x // special case
    30  	}
    31  	sign := false
    32  	if x < 0 {
    33  		x = -x
    34  		sign = true
    35  	}
    36  	if x > 1 {
    37  		return NaN() // special case
    38  	}
    39  
    40  	temp := Sqrt(1 - x*x)
    41  	if x > 0.7 {
    42  		temp = Pi/2 - satan(temp/x)
    43  	} else {
    44  		temp = satan(x / temp)
    45  	}
    46  
    47  	if sign {
    48  		temp = -temp
    49  	}
    50  	return temp
    51  }
    52  
    53  // Acos returns the arccosine, in radians, of x.
    54  //
    55  // Special case is:
    56  //
    57  //	Acos(x) = NaN if x < -1 or x > 1
    58  func Acos(x float64) float64 {
    59  	if haveArchAcos {
    60  		return archAcos(x)
    61  	}
    62  	return acos(x)
    63  }
    64  
    65  func acos(x float64) float64 {
    66  	return Pi/2 - Asin(x)
    67  }