libm/math/
cosf.rs

1/* origin: FreeBSD /usr/src/lib/msun/src/s_cosf.c */
2/*
3 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
4 * Optimized by Bruce D. Evans.
5 */
6/*
7 * ====================================================
8 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
9 *
10 * Developed at SunPro, a Sun Microsystems, Inc. business.
11 * Permission to use, copy, modify, and distribute this
12 * software is freely granted, provided that this notice
13 * is preserved.
14 * ====================================================
15 */
16
17use super::{k_cosf, k_sinf, rem_pio2f};
18
19use core::f64::consts::FRAC_PI_2;
20
21/* Small multiples of pi/2 rounded to double precision. */
22const C1_PIO2: f64 = 1. * FRAC_PI_2; /* 0x3FF921FB, 0x54442D18 */
23const C2_PIO2: f64 = 2. * FRAC_PI_2; /* 0x400921FB, 0x54442D18 */
24const C3_PIO2: f64 = 3. * FRAC_PI_2; /* 0x4012D97C, 0x7F3321D2 */
25const C4_PIO2: f64 = 4. * FRAC_PI_2; /* 0x401921FB, 0x54442D18 */
26
27#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
28pub fn cosf(x: f32) -> f32 {
29    let x64 = x as f64;
30
31    let x1p120 = f32::from_bits(0x7b800000); // 0x1p120f === 2 ^ 120
32
33    let mut ix = x.to_bits();
34    let sign = (ix >> 31) != 0;
35    ix &= 0x7fffffff;
36
37    if ix <= 0x3f490fda {
38        /* |x| ~<= pi/4 */
39        if ix < 0x39800000 {
40            /* |x| < 2**-12 */
41            /* raise inexact if x != 0 */
42            force_eval!(x + x1p120);
43            return 1.;
44        }
45        return k_cosf(x64);
46    }
47    if ix <= 0x407b53d1 {
48        /* |x| ~<= 5*pi/4 */
49        if ix > 0x4016cbe3 {
50            /* |x|  ~> 3*pi/4 */
51            return -k_cosf(if sign { x64 + C2_PIO2 } else { x64 - C2_PIO2 });
52        } else if sign {
53            return k_sinf(x64 + C1_PIO2);
54        } else {
55            return k_sinf(C1_PIO2 - x64);
56        }
57    }
58    if ix <= 0x40e231d5 {
59        /* |x| ~<= 9*pi/4 */
60        if ix > 0x40afeddf {
61            /* |x| ~> 7*pi/4 */
62            return k_cosf(if sign { x64 + C4_PIO2 } else { x64 - C4_PIO2 });
63        } else if sign {
64            return k_sinf(-x64 - C3_PIO2);
65        } else {
66            return k_sinf(x64 - C3_PIO2);
67        }
68    }
69
70    /* cos(Inf or NaN) is NaN */
71    if ix >= 0x7f800000 {
72        return x - x;
73    }
74
75    /* general argument reduction needed */
76    let (n, y) = rem_pio2f(x);
77    match n & 3 {
78        0 => k_cosf(y),
79        1 => k_sinf(-y),
80        2 => -k_cosf(y),
81        _ => k_sinf(y),
82    }
83}