github.com/AESNooper/go/src@v0.0.0-20220218095104-b56a4ab1bbbb/math/atan2.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  // Atan2 returns the arc tangent of y/x, using
     8  // the signs of the two to determine the quadrant
     9  // of the return value.
    10  //
    11  // Special cases are (in order):
    12  //	Atan2(y, NaN) = NaN
    13  //	Atan2(NaN, x) = NaN
    14  //	Atan2(+0, x>=0) = +0
    15  //	Atan2(-0, x>=0) = -0
    16  //	Atan2(+0, x<=-0) = +Pi
    17  //	Atan2(-0, x<=-0) = -Pi
    18  //	Atan2(y>0, 0) = +Pi/2
    19  //	Atan2(y<0, 0) = -Pi/2
    20  //	Atan2(+Inf, +Inf) = +Pi/4
    21  //	Atan2(-Inf, +Inf) = -Pi/4
    22  //	Atan2(+Inf, -Inf) = 3Pi/4
    23  //	Atan2(-Inf, -Inf) = -3Pi/4
    24  //	Atan2(y, +Inf) = 0
    25  //	Atan2(y>0, -Inf) = +Pi
    26  //	Atan2(y<0, -Inf) = -Pi
    27  //	Atan2(+Inf, x) = +Pi/2
    28  //	Atan2(-Inf, x) = -Pi/2
    29  func Atan2(y, x float64) float64 {
    30  	if haveArchAtan2 {
    31  		return archAtan2(y, x)
    32  	}
    33  	return atan2(y, x)
    34  }
    35  
    36  func atan2(y, x float64) float64 {
    37  	// special cases
    38  	switch {
    39  	case IsNaN(y) || IsNaN(x):
    40  		return NaN()
    41  	case y == 0:
    42  		if x >= 0 && !Signbit(x) {
    43  			return Copysign(0, y)
    44  		}
    45  		return Copysign(Pi, y)
    46  	case x == 0:
    47  		return Copysign(Pi/2, y)
    48  	case IsInf(x, 0):
    49  		if IsInf(x, 1) {
    50  			switch {
    51  			case IsInf(y, 0):
    52  				return Copysign(Pi/4, y)
    53  			default:
    54  				return Copysign(0, y)
    55  			}
    56  		}
    57  		switch {
    58  		case IsInf(y, 0):
    59  			return Copysign(3*Pi/4, y)
    60  		default:
    61  			return Copysign(Pi, y)
    62  		}
    63  	case IsInf(y, 0):
    64  		return Copysign(Pi/2, y)
    65  	}
    66  
    67  	// Call atan and determine the quadrant.
    68  	q := Atan(y / x)
    69  	if x < 0 {
    70  		if q <= 0 {
    71  			return q + Pi
    72  		}
    73  		return q - Pi
    74  	}
    75  	return q
    76  }