77 lines
1.8 KiB
Go
77 lines
1.8 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package math
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// Atan2 returns the arc tangent of y/x, using
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// the signs of the two to determine the quadrant
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// of the return value.
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//
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// Special cases are (in order):
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// Atan2(y, NaN) = NaN
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// Atan2(NaN, x) = NaN
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// Atan2(+0, x>=0) = +0
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// Atan2(-0, x>=0) = -0
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// Atan2(+0, x<=-0) = +Pi
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// Atan2(-0, x<=-0) = -Pi
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// Atan2(y>0, 0) = +Pi/2
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// Atan2(y<0, 0) = -Pi/2
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// Atan2(+Inf, +Inf) = +Pi/4
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// Atan2(-Inf, +Inf) = -Pi/4
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// Atan2(+Inf, -Inf) = 3Pi/4
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// Atan2(-Inf, -Inf) = -3Pi/4
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// Atan2(y, +Inf) = 0
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// Atan2(y>0, -Inf) = +Pi
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// Atan2(y<0, -Inf) = -Pi
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// Atan2(+Inf, x) = +Pi/2
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// Atan2(-Inf, x) = -Pi/2
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func libc_atan2(float64, float64) float64 __asm__("atan2")
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func Atan2(y, x float64) float64 {
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return libc_atan2(y, x)
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}
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func atan2(y, x float64) float64 {
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// TODO(rsc): Remove manual inlining of IsNaN, IsInf
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// when compiler does it for us
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// special cases
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switch {
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case y != y || x != x: // IsNaN(y) || IsNaN(x):
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return NaN()
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case y == 0:
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if x >= 0 && !Signbit(x) {
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return Copysign(0, y)
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}
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return Copysign(Pi, y)
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case x == 0:
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return Copysign(Pi/2, y)
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case x < -MaxFloat64 || x > MaxFloat64: // IsInf(x, 0):
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if x > MaxFloat64 { // IsInf(x, 1) {
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switch {
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case y < -MaxFloat64 || y > MaxFloat64: // IsInf(y, -1) || IsInf(y, 1):
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return Copysign(Pi/4, y)
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default:
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return Copysign(0, y)
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}
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}
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switch {
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case y < -MaxFloat64 || y > MaxFloat64: // IsInf(y, -1) || IsInf(y, 1):
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return Copysign(3*Pi/4, y)
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default:
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return Copysign(Pi, y)
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}
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case y < -MaxFloat64 || y > MaxFloat64: //IsInf(y, 0):
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return Copysign(Pi/2, y)
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}
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// Call atan and determine the quadrant.
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q := Atan(y / x)
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if x < 0 {
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if q <= 0 {
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return q + Pi
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}
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return q - Pi
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}
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return q
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}
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