1/* origin: FreeBSD /usr/src/lib/msun/src/k_tan.c */
2/*
3 * ====================================================
4 * Copyright 2004 Sun Microsystems, Inc. All Rights Reserved.
5 *
6 * Permission to use, copy, modify, and distribute this
7 * software is freely granted, provided that this notice
8 * is preserved.
9 * ====================================================
10 */
11
12/* |tan(x)/x - t(x)| < 2**-25.5 (~[-2e-08, 2e-08]). */
13const T: [f64; 6] = [
14 0.333331395030791399758, /* 0x15554d3418c99f.0p-54 */
15 0.133392002712976742718, /* 0x1112fd38999f72.0p-55 */
16 0.0533812378445670393523, /* 0x1b54c91d865afe.0p-57 */
17 0.0245283181166547278873, /* 0x191df3908c33ce.0p-58 */
18 0.00297435743359967304927, /* 0x185dadfcecf44e.0p-61 */
19 0.00946564784943673166728, /* 0x1362b9bf971bcd.0p-59 */
20];
21
22#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
23pub(crate) fn k_tanf(x: f64, odd: bool) -> f32 {
24 let z: f64 = x * x;
25 /*
26 * Split up the polynomial into small independent terms to give
27 * opportunities for parallel evaluation. The chosen splitting is
28 * micro-optimized for Athlons (XP, X64). It costs 2 multiplications
29 * relative to Horner's method on sequential machines.
30 *
31 * We add the small terms from lowest degree up for efficiency on
32 * non-sequential machines (the lowest degree terms tend to be ready
33 * earlier). Apart from this, we don't care about order of
34 * operations, and don't need to to care since we have precision to
35 * spare. However, the chosen splitting is good for accuracy too,
36 * and would give results as accurate as Horner's method if the
37 * small terms were added from highest degree down.
38 */
39 let mut r: f64 = T[4] + z * T[5];
40 let t: f64 = T[2] + z * T[3];
41 let w: f64 = z * z;
42 let s: f64 = z * x;
43 let u: f64 = T[0] + z * T[1];
44 r = (x + s * u) + (s * w) * (t + w * r);
45 (if odd { -1. / r } else { r }) as f32
46}
47