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 31 func atan2(y, x float64) float64 { 32 // special cases 33 switch { 34 case IsNaN(y) || IsNaN(x): 35 return NaN() 36 case y == 0: 37 if x >= 0 && !Signbit(x) { 38 return Copysign(0, y) 39 } 40 return Copysign(Pi, y) 41 case x == 0: 42 return Copysign(Pi/2, y) 43 case IsInf(x, 0): 44 if IsInf(x, 1) { 45 switch { 46 case IsInf(y, 0): 47 return Copysign(Pi/4, y) 48 default: 49 return Copysign(0, y) 50 } 51 } 52 switch { 53 case IsInf(y, 0): 54 return Copysign(3*Pi/4, y) 55 default: 56 return Copysign(Pi, y) 57 } 58 case IsInf(y, 0): 59 return Copysign(Pi/2, y) 60 } 61 62 // Call atan and determine the quadrant. 63 q := Atan(y / x) 64 if x < 0 { 65 if q <= 0 { 66 return q + Pi 67 } 68 return q - Pi 69 } 70 return q 71 } 72
