golang atan2 代码
文件路径：/src/math/atan2.go
/ 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
}