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.
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.
11 // Special cases are (in order):
13 // Atan2(y, NaN) = NaN
14 // Atan2(NaN, x) = NaN
15 // Atan2(+0, x>=0) = +0
16 // Atan2(-0, x>=0) = -0
17 // Atan2(+0, x<=-0) = +Pi
18 // Atan2(-0, x<=-0) = -Pi
19 // Atan2(y>0, 0) = +Pi/2
20 // Atan2(y<0, 0) = -Pi/2
21 // Atan2(+Inf, +Inf) = +Pi/4
22 // Atan2(-Inf, +Inf) = -Pi/4
23 // Atan2(+Inf, -Inf) = 3Pi/4
24 // Atan2(-Inf, -Inf) = -3Pi/4
26 // Atan2(y>0, -Inf) = +Pi
27 // Atan2(y<0, -Inf) = -Pi
28 // Atan2(+Inf, x) = +Pi/2
29 // Atan2(-Inf, x) = -Pi/2
30 func Atan2(y, x float64) float64 {
32 return archAtan2(y, x)
37 func atan2(y, x float64) float64 {
40 case IsNaN(y) || IsNaN(x):
43 if x >= 0 && !Signbit(x) {
46 return Copysign(Pi, y)
48 return Copysign(Pi/2, y)
53 return Copysign(Pi/4, y)
60 return Copysign(3*Pi/4, y)
62 return Copysign(Pi, y)
65 return Copysign(Pi/2, y)
68 // Call atan and determine the quadrant.