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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 // Atan2 returns the arc tangent of y/x, using // the signs of the two to determine the quadrant // of the return value. // // Special cases are (in order): // Atan2(y, NaN) = NaN // Atan2(NaN, x) = NaN // Atan2(+0, x>=0) = +0 // Atan2(-0, x>=0) = -0 // Atan2(+0, x<=-0) = +Pi // Atan2(-0, x<=-0) = -Pi // Atan2(y>0, 0) = +Pi/2 // Atan2(y<0, 0) = -Pi/2 // Atan2(+Inf, +Inf) = +Pi/4 // Atan2(-Inf, +Inf) = -Pi/4 // Atan2(+Inf, -Inf) = 3Pi/4 // Atan2(-Inf, -Inf) = -3Pi/4 // Atan2(y, +Inf) = 0 // Atan2(y>0, -Inf) = +Pi // Atan2(y<0, -Inf) = -Pi // Atan2(+Inf, x) = +Pi/2 // Atan2(-Inf, x) = -Pi/2 func Atan2(y, x float64) float64 { if haveArchAtan2 { return archAtan2(y, x) } return atan2(y, x) } func atan2(y, x float64) float64 { // special cases switch { case IsNaN(y) || IsNaN(x): return NaN() case y == 0: if x >= 0 && !Signbit(x) { return Copysign(0, y) } return Copysign(Pi, y) case x == 0: return Copysign(Pi/2, y) case IsInf(x, 0): if IsInf(x, 1) { switch { case IsInf(y, 0): return Copysign(Pi/4, y) default: return Copysign(0, y) } } switch { case IsInf(y, 0): return Copysign(3*Pi/4, y) default: return Copysign(Pi, y) } case IsInf(y, 0): return Copysign(Pi/2, y) } // Call atan and determine the quadrant. q := Atan(y / x) if x < 0 { if q <= 0 { return q + Pi } return q - Pi } return q }