libm/math/
cos.rs

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
12use 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)]
49pub 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}
libm/math/cos.rs

libm/math/
cos.rs
