Black Lives Matter. Support the Equal Justice Initiative.

# Source file src/math/atan2.go

## Documentation: math

```     1  // Copyright 2009 The Go Authors. All rights reserved.
2  // Use of this source code is governed by a BSD-style
4
5  package math
6
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.
10  //
11  // Special cases are (in order):
12  //	Atan2(y, NaN) = NaN
13  //	Atan2(NaN, x) = NaN
14  //	Atan2(+0, x>=0) = +0
15  //	Atan2(-0, x>=0) = -0
16  //	Atan2(+0, x<=-0) = +Pi
17  //	Atan2(-0, x<=-0) = -Pi
18  //	Atan2(y>0, 0) = +Pi/2
19  //	Atan2(y<0, 0) = -Pi/2
20  //	Atan2(+Inf, +Inf) = +Pi/4
21  //	Atan2(-Inf, +Inf) = -Pi/4
22  //	Atan2(+Inf, -Inf) = 3Pi/4
23  //	Atan2(-Inf, -Inf) = -3Pi/4
24  //	Atan2(y, +Inf) = 0
25  //	Atan2(y>0, -Inf) = +Pi
26  //	Atan2(y<0, -Inf) = -Pi
27  //	Atan2(+Inf, x) = +Pi/2
28  //	Atan2(-Inf, x) = -Pi/2
29  func Atan2(y, x float64) float64 {
30  	if haveArchAtan2 {
31  		return archAtan2(y, x)
32  	}
33  	return atan2(y, x)
34  }
35
36  func atan2(y, x float64) float64 {
37  	// special cases
38  	switch {
39  	case IsNaN(y) || IsNaN(x):
40  		return NaN()
41  	case y == 0:
42  		if x >= 0 && !Signbit(x) {
43  			return Copysign(0, y)
44  		}
45  		return Copysign(Pi, y)
46  	case x == 0:
47  		return Copysign(Pi/2, y)
48  	case IsInf(x, 0):
49  		if IsInf(x, 1) {
50  			switch {
51  			case IsInf(y, 0):
52  				return Copysign(Pi/4, y)
53  			default:
54  				return Copysign(0, y)
55  			}
56  		}
57  		switch {
58  		case IsInf(y, 0):
59  			return Copysign(3*Pi/4, y)
60  		default:
61  			return Copysign(Pi, y)
62  		}
63  	case IsInf(y, 0):
64  		return Copysign(Pi/2, y)
65  	}
66
67  	// Call atan and determine the quadrant.
68  	q := Atan(y / x)
69  	if x < 0 {
70  		if q <= 0 {
71  			return q + Pi
72  		}
73  		return q - Pi
74  	}
75  	return q
76  }
77
```

View as plain text