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 core::f64::consts::FRAC_PI_2;
18
19use super::{k_cosf, k_sinf, rem_pio2f};
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/// The cosine of `x` (f32).
28///
29/// `x` is specified in radians.
30#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
31pub fn cosf(x: f32) -> f32 {
32    let x64 = x as f64;
33
34    let x1p120 = f32::from_bits(0x7b800000); // 0x1p120f === 2 ^ 120
35
36    let mut ix = x.to_bits();
37    let sign = (ix >> 31) != 0;
38    ix &= 0x7fffffff;
39
40    if ix <= 0x3f490fda {
41        /* |x| ~<= pi/4 */
42        if ix < 0x39800000 {
43            /* |x| < 2**-12 */
44            /* raise inexact if x != 0 */
45            force_eval!(x + x1p120);
46            return 1.;
47        }
48        return k_cosf(x64);
49    }
50    if ix <= 0x407b53d1 {
51        /* |x| ~<= 5*pi/4 */
52        if ix > 0x4016cbe3 {
53            /* |x|  ~> 3*pi/4 */
54            return -k_cosf(if sign { x64 + C2_PIO2 } else { x64 - C2_PIO2 });
55        } else if sign {
56            return k_sinf(x64 + C1_PIO2);
57        } else {
58            return k_sinf(C1_PIO2 - x64);
59        }
60    }
61    if ix <= 0x40e231d5 {
62        /* |x| ~<= 9*pi/4 */
63        if ix > 0x40afeddf {
64            /* |x| ~> 7*pi/4 */
65            return k_cosf(if sign { x64 + C4_PIO2 } else { x64 - C4_PIO2 });
66        } else if sign {
67            return k_sinf(-x64 - C3_PIO2);
68        } else {
69            return k_sinf(x64 - C3_PIO2);
70        }
71    }
72
73    /* cos(Inf or NaN) is NaN */
74    if ix >= 0x7f800000 {
75        return x - x;
76    }
77
78    /* general argument reduction needed */
79    let (n, y) = rem_pio2f(x);
80    match n & 3 {
81        0 => k_cosf(y),
82        1 => k_sinf(-y),
83        2 => -k_cosf(y),
84        _ => k_sinf(y),
85    }
86}
libm/math/cosf.rs

libm/math/
cosf.rs
