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
45 /// The cosine of `x` (f64).
46 ///
47 /// `x` is specified in radians.
48 #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
cos(x: f64) -> f6449 pub fn cos(x: f64) -> f64 {
50 let ix = (f64::to_bits(x) >> 32) as u32 & 0x7fffffff;
51
52 /* |x| ~< pi/4 */
53 if ix <= 0x3fe921fb {
54 if ix < 0x3e46a09e {
55 /* if x < 2**-27 * sqrt(2) */
56 /* raise inexact if x != 0 */
57 if x as i32 == 0 {
58 return 1.0;
59 }
60 }
61 return k_cos(x, 0.0);
62 }
63
64 /* cos(Inf or NaN) is NaN */
65 if ix >= 0x7ff00000 {
66 return x - x;
67 }
68
69 /* argument reduction needed */
70 let (n, y0, y1) = rem_pio2(x);
71 match n & 3 {
72 0 => k_cos(y0, y1),
73 1 => -k_sin(y0, y1, 1),
74 2 => -k_cos(y0, y1),
75 _ => k_sin(y0, y1, 1),
76 }
77 }
78