1 | /* origin: FreeBSD /usr/src/lib/msun/src/e_atan2f.c */ |
2 | /* |
3 | * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. |
4 | */ |
5 | /* |
6 | * ==================================================== |
7 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
8 | * |
9 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
10 | * Permission to use, copy, modify, and distribute this |
11 | * software is freely granted, provided that this notice |
12 | * is preserved. |
13 | * ==================================================== |
14 | */ |
15 | |
16 | use super::atanf; |
17 | use super::fabsf; |
18 | |
19 | const PI: f32 = 3.1415927410e+00; /* 0x40490fdb */ |
20 | const PI_LO: f32 = -8.7422776573e-08; /* 0xb3bbbd2e */ |
21 | |
22 | /// Arctangent of y/x (f32) |
23 | /// |
24 | /// Computes the inverse tangent (arc tangent) of `y/x`. |
25 | /// Produces the correct result even for angles near pi/2 or -pi/2 (that is, when `x` is near 0). |
26 | /// Returns a value in radians, in the range of -pi to pi. |
27 | #[cfg_attr (all(test, assert_no_panic), no_panic::no_panic)] |
28 | pub fn atan2f(y: f32, x: f32) -> f32 { |
29 | if x.is_nan() || y.is_nan() { |
30 | return x + y; |
31 | } |
32 | let mut ix = x.to_bits(); |
33 | let mut iy = y.to_bits(); |
34 | |
35 | if ix == 0x3f800000 { |
36 | /* x=1.0 */ |
37 | return atanf(y); |
38 | } |
39 | let m = ((iy >> 31) & 1) | ((ix >> 30) & 2); /* 2*sign(x)+sign(y) */ |
40 | ix &= 0x7fffffff; |
41 | iy &= 0x7fffffff; |
42 | |
43 | /* when y = 0 */ |
44 | if iy == 0 { |
45 | return match m { |
46 | 0 | 1 => y, /* atan(+-0,+anything)=+-0 */ |
47 | 2 => PI, /* atan(+0,-anything) = pi */ |
48 | 3 | _ => -PI, /* atan(-0,-anything) =-pi */ |
49 | }; |
50 | } |
51 | /* when x = 0 */ |
52 | if ix == 0 { |
53 | return if m & 1 != 0 { -PI / 2. } else { PI / 2. }; |
54 | } |
55 | /* when x is INF */ |
56 | if ix == 0x7f800000 { |
57 | return if iy == 0x7f800000 { |
58 | match m { |
59 | 0 => PI / 4., /* atan(+INF,+INF) */ |
60 | 1 => -PI / 4., /* atan(-INF,+INF) */ |
61 | 2 => 3. * PI / 4., /* atan(+INF,-INF)*/ |
62 | 3 | _ => -3. * PI / 4., /* atan(-INF,-INF)*/ |
63 | } |
64 | } else { |
65 | match m { |
66 | 0 => 0., /* atan(+...,+INF) */ |
67 | 1 => -0., /* atan(-...,+INF) */ |
68 | 2 => PI, /* atan(+...,-INF) */ |
69 | 3 | _ => -PI, /* atan(-...,-INF) */ |
70 | } |
71 | }; |
72 | } |
73 | /* |y/x| > 0x1p26 */ |
74 | if (ix + (26 << 23) < iy) || (iy == 0x7f800000) { |
75 | return if m & 1 != 0 { -PI / 2. } else { PI / 2. }; |
76 | } |
77 | |
78 | /* z = atan(|y/x|) with correct underflow */ |
79 | let z = if (m & 2 != 0) && (iy + (26 << 23) < ix) { |
80 | /*|y/x| < 0x1p-26, x < 0 */ |
81 | 0. |
82 | } else { |
83 | atanf(fabsf(y / x)) |
84 | }; |
85 | match m { |
86 | 0 => z, /* atan(+,+) */ |
87 | 1 => -z, /* atan(-,+) */ |
88 | 2 => PI - (z - PI_LO), /* atan(+,-) */ |
89 | _ => (z - PI_LO) - PI, /* case 3 */ /* atan(-,-) */ |
90 | } |
91 | } |
92 | |