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]). */ |
13 | const 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)] |
23 | pub(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 | |