| // 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 { |
| // TODO(rsc): Remove manual inlining of IsNaN, IsInf |
| // when compiler does it for us |
| // special cases |
| switch { |
| case y != y || x != x: // 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 x < -MaxFloat64 || x > MaxFloat64: // IsInf(x, 0): |
| if x > MaxFloat64 { // IsInf(x, 1) { |
| switch { |
| case y < -MaxFloat64 || y > MaxFloat64: // IsInf(y, -1) || IsInf(y, 1): |
| return Copysign(Pi/4, y) |
| default: |
| return Copysign(0, y) |
| } |
| } |
| switch { |
| case y < -MaxFloat64 || y > MaxFloat64: // IsInf(y, -1) || IsInf(y, 1): |
| return Copysign(3*Pi/4, y) |
| default: |
| return Copysign(Pi, y) |
| } |
| case y < -MaxFloat64 || y > MaxFloat64: //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 |
| } |