| /* 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 |
| } |
