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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 | ||
48663c56 | 22 | #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] |
dc9dc135 | 23 | pub(crate) fn k_tanf(x: f64, odd: bool) -> f32 { |
8faf50e0 XL |
24 | let z = 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 = T[4] + z * T[5]; | |
40 | let t = T[2] + z * T[3]; | |
41 | let w = z * z; | |
42 | let s = z * x; | |
43 | let u = 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 | } |