const_soft_float/soft_f64/
cos.rs

1// origin: FreeBSD /usr/src/lib/msun/src/s_cos.c */,
2// https://github.com/rust-lang/libm/blob/4c8a973741c014b11ce7f1477693a3e5d4ef9609/src/math/cos.rs
3//
4// ====================================================
5// Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6//
7// Developed at SunPro, a Sun Microsystems, Inc. business.
8// Permission to use, copy, modify, and distribute this
9// software is freely granted, provided that this notice
10// is preserved.
11// ====================================================
12
13use super::{
14    helpers::{k_cos, k_sin, rem_pio2},
15    SoftF64,
16};
17
18// cos(x)
19// Return cosine function of x.
20//
21// kernel function:
22//      k_sin           ... sine function on [-pi/4,pi/4]
23//      k_cos           ... cosine function on [-pi/4,pi/4]
24//      rem_pio2        ... argument reduction routine
25//
26// Method.
27//      Let S,C and T denote the sin, cos and tan respectively on
28//      [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
29//      in [-pi/4 , +pi/4], and let n = k mod 4.
30//      We have
31//
32//          n        sin(x)      cos(x)        tan(x)
33//     ----------------------------------------------------------
34//          0          S           C             T
35//          1          C          -S            -1/T
36//          2         -S          -C             T
37//          3         -C           S            -1/T
38//     ----------------------------------------------------------
39//
40// Special cases:
41//      Let trig be any of sin, cos, or tan.
42//      trig(+-INF)  is NaN, with signals;
43//      trig(NaN)    is that NaN;
44//
45// Accuracy:
46//      TRIG(x) returns trig(x) nearly rounded
47//
48pub(crate) const fn cos(x: SoftF64) -> SoftF64 {
49    let ix = (SoftF64::to_bits(x) >> 32) as u32 & 0x7fffffff;
50
51    /* |x| ~< pi/4 */
52    if ix <= 0x3fe921fb {
53        if ix < 0x3e46a09e {
54            /* if x < 2**-27 * sqrt(2) */
55            /* raise inexact if x != 0 */
56            if x.0 as i32 == 0 {
57                return SoftF64::ONE;
58            }
59        }
60        return k_cos(x, SoftF64::ZERO);
61    }
62
63    /* cos(Inf or NaN) is NaN */
64    if ix >= 0x7ff00000 {
65        return x.sub(x);
66    }
67
68    /* argument reduction needed */
69    let (n, y0, y1) = rem_pio2(x);
70    match n & 3 {
71        0 => k_cos(y0, y1),
72        1 => k_sin(y0, y1, 1).neg(),
73        2 => k_cos(y0, y1).neg(),
74        _ => k_sin(y0, y1, 1),
75    }
76}
77
78#[cfg(test)]
79mod test {
80    use crate::soft_f64::SoftF64;
81
82    #[test]
83    fn test_large_neg() {
84        assert_eq!(SoftF64(-1647101.0).cos().to_f64(), (-1647101.0_f64).cos())
85    }
86}
const_soft_float/soft_f64/cos.rs

const_soft_float/soft_f64/
cos.rs
