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