sincos.rs - source
Description: Source of the Rust file `/Users/erlendbasso/.cargo/registry/src/github.com-1ecc6299db9ec823/libm-0.2.6/src/math/sincos.rs`.
Keywords: rust, rustlang, rust-lang

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    /* origin: FreeBSD /usr/src/lib/msun/src/s_sin.c */
    /*
     * ====================================================
     * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
     *
     * Developed at SunPro, a Sun Microsystems, Inc. business.
     * Permission to use, copy, modify, and distribute this
     * software is freely granted, provided that this notice
     * is preserved.
     * ====================================================
     */

    use super::{get_high_word, k_cos, k_sin, rem_pio2};

    #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
    pub fn sincos(x: f64) -> (f64, f64) {
        let s: f64;
        let c: f64;
        let mut ix: u32;

        ix = get_high_word(x);
        ix &= 0x7fffffff;

        /* |x| ~< pi/4 */
        if ix <= 0x3fe921fb {
            /* if |x| < 2**-27 * sqrt(2) */
            if ix < 0x3e46a09e {
                /* raise inexact if x!=0 and underflow if subnormal */
                let x1p120 = f64::from_bits(0x4770000000000000); // 0x1p120 == 2^120
                if ix < 0x00100000 {
                    force_eval!(x / x1p120);
                } else {
                    force_eval!(x + x1p120);
                }
                return (x, 1.0);
            }
            return (k_sin(x, 0.0, 0), k_cos(x, 0.0));
        }

        /* sincos(Inf or NaN) is NaN */
        if ix >= 0x7ff00000 {
            let rv = x - x;
            return (rv, rv);
        }

        /* argument reduction needed */
        let (n, y0, y1) = rem_pio2(x);
        s = k_sin(y0, y1, 1);
        c = k_cos(y0, y1);
        match n & 3 {
            0 => (s, c),
            1 => (c, -s),
            2 => (-s, -c),
            3 => (-c, s),
            #[cfg(debug_assertions)]
            _ => unreachable!(),
            #[cfg(not(debug_assertions))]
            _ => (0.0, 1.0),
        }
    }

    // These tests are based on those from sincosf.rs
    #[cfg(test)]
    mod tests {
        use super::sincos;

        const TOLERANCE: f64 = 1e-6;

        #[test]
        fn with_pi() {
            let (s, c) = sincos(core::f64::consts::PI);
            assert!(
                (s - 0.0).abs() < TOLERANCE,
                "|{} - {}| = {} >= {}",
                s,
                0.0,
                (s - 0.0).abs(),
                TOLERANCE
            );
            assert!(
                (c + 1.0).abs() < TOLERANCE,
                "|{} + {}| = {} >= {}",
                c,
                1.0,
                (s + 1.0).abs(),
                TOLERANCE
            );
        }

        #[test]
        fn rotational_symmetry() {
            use core::f64::consts::PI;
            const N: usize = 24;
            for n in 0..N {
                let theta = 2. * PI * (n as f64) / (N as f64);
                let (s, c) = sincos(theta);
                let (s_plus, c_plus) = sincos(theta + 2. * PI);
                let (s_minus, c_minus) = sincos(theta - 2. * PI);

                assert!(
                    (s - s_plus).abs() < TOLERANCE,
                    "|{} - {}| = {} >= {}",
                    s,
                    s_plus,
                    (s - s_plus).abs(),
                    TOLERANCE
                );
                assert!(
                    (s - s_minus).abs() < TOLERANCE,
                    "|{} - {}| = {} >= {}",
                    s,
                    s_minus,
                    (s - s_minus).abs(),
                    TOLERANCE
                );
                assert!(
                    (c - c_plus).abs() < TOLERANCE,
                    "|{} - {}| = {} >= {}",
                    c,
                    c_plus,
                    (c - c_plus).abs(),
                    TOLERANCE
                );
                assert!(
                    (c - c_minus).abs() < TOLERANCE,
                    "|{} - {}| = {} >= {}",
                    c,
                    c_minus,
                    (c - c_minus).abs(),
                    TOLERANCE
                );
            }
        }
    }