1 | // origin: FreeBSD /usr/src/lib/msun/src/s_cos.c */ |
2 | // |
3 | // ==================================================== |
4 | // Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
5 | // |
6 | // Developed at SunPro, a Sun Microsystems, Inc. business. |
7 | // Permission to use, copy, modify, and distribute this |
8 | // software is freely granted, provided that this notice |
9 | // is preserved. |
10 | // ==================================================== |
11 | |
12 | use super::{k_cos, k_sin, rem_pio2}; |
13 | |
14 | // cos(x) |
15 | // Return cosine function of x. |
16 | // |
17 | // kernel function: |
18 | // k_sin ... sine function on [-pi/4,pi/4] |
19 | // k_cos ... cosine function on [-pi/4,pi/4] |
20 | // rem_pio2 ... argument reduction routine |
21 | // |
22 | // Method. |
23 | // Let S,C and T denote the sin, cos and tan respectively on |
24 | // [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 |
25 | // in [-pi/4 , +pi/4], and let n = k mod 4. |
26 | // We have |
27 | // |
28 | // n sin(x) cos(x) tan(x) |
29 | // ---------------------------------------------------------- |
30 | // 0 S C T |
31 | // 1 C -S -1/T |
32 | // 2 -S -C T |
33 | // 3 -C S -1/T |
34 | // ---------------------------------------------------------- |
35 | // |
36 | // Special cases: |
37 | // Let trig be any of sin, cos, or tan. |
38 | // trig(+-INF) is NaN, with signals; |
39 | // trig(NaN) is that NaN; |
40 | // |
41 | // Accuracy: |
42 | // TRIG(x) returns trig(x) nearly rounded |
43 | // |
44 | #[cfg_attr (all(test, assert_no_panic), no_panic::no_panic)] |
45 | pub fn cos(x: f64) -> f64 { |
46 | let ix = (f64::to_bits(x) >> 32) as u32 & 0x7fffffff; |
47 | |
48 | /* |x| ~< pi/4 */ |
49 | if ix <= 0x3fe921fb { |
50 | if ix < 0x3e46a09e { |
51 | /* if x < 2**-27 * sqrt(2) */ |
52 | /* raise inexact if x != 0 */ |
53 | if x as i32 == 0 { |
54 | return 1.0; |
55 | } |
56 | } |
57 | return k_cos(x, 0.0); |
58 | } |
59 | |
60 | /* cos(Inf or NaN) is NaN */ |
61 | if ix >= 0x7ff00000 { |
62 | return x - x; |
63 | } |
64 | |
65 | /* argument reduction needed */ |
66 | let (n, y0, y1) = rem_pio2(x); |
67 | match n & 3 { |
68 | 0 => k_cos(y0, y1), |
69 | 1 => -k_sin(y0, y1, 1), |
70 | 2 => -k_cos(y0, y1), |
71 | _ => k_sin(y0, y1, 1), |
72 | } |
73 | } |
74 | |