1 | /* origin: FreeBSD /usr/src/lib/msun/src/e_rem_pio2f.c */ |
2 | /* |
3 | * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. |
4 | * Debugged and optimized by Bruce D. Evans. |
5 | */ |
6 | /* |
7 | * ==================================================== |
8 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
9 | * |
10 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
11 | * Permission to use, copy, modify, and distribute this |
12 | * software is freely granted, provided that this notice |
13 | * is preserved. |
14 | * ==================================================== |
15 | */ |
16 | |
17 | use super::rem_pio2_large; |
18 | |
19 | use core::f64; |
20 | |
21 | const TOINT: f64 = 1.5 / f64::EPSILON; |
22 | |
23 | /// 53 bits of 2/pi |
24 | const INV_PIO2: f64 = 6.36619772367581382433e-01; /* 0x3FE45F30, 0x6DC9C883 */ |
25 | /// first 25 bits of pi/2 |
26 | const PIO2_1: f64 = 1.57079631090164184570e+00; /* 0x3FF921FB, 0x50000000 */ |
27 | /// pi/2 - pio2_1 |
28 | const PIO2_1T: f64 = 1.58932547735281966916e-08; /* 0x3E5110b4, 0x611A6263 */ |
29 | |
30 | /// Return the remainder of x rem pi/2 in *y |
31 | /// |
32 | /// use double precision for everything except passing x |
33 | /// use __rem_pio2_large() for large x |
34 | #[cfg_attr (all(test, assert_no_panic), no_panic::no_panic)] |
35 | pub(crate) fn rem_pio2f(x: f32) -> (i32, f64) { |
36 | let x64 = x as f64; |
37 | |
38 | let mut tx: [f64; 1] = [0.]; |
39 | let mut ty: [f64; 1] = [0.]; |
40 | |
41 | let ix = x.to_bits() & 0x7fffffff; |
42 | /* 25+53 bit pi is good enough for medium size */ |
43 | if ix < 0x4dc90fdb { |
44 | /* |x| ~< 2^28*(pi/2), medium size */ |
45 | /* Use a specialized rint() to get fn. Assume round-to-nearest. */ |
46 | let tmp = x64 * INV_PIO2 + TOINT; |
47 | // force rounding of tmp to it's storage format on x87 to avoid |
48 | // excess precision issues. |
49 | #[cfg (all(target_arch = "x86" , not(target_feature = "sse2" )))] |
50 | let tmp = force_eval!(tmp); |
51 | let f_n = tmp - TOINT; |
52 | return (f_n as i32, x64 - f_n * PIO2_1 - f_n * PIO2_1T); |
53 | } |
54 | if ix >= 0x7f800000 { |
55 | /* x is inf or NaN */ |
56 | return (0, x64 - x64); |
57 | } |
58 | /* scale x into [2^23, 2^24-1] */ |
59 | let sign = (x.to_bits() >> 31) != 0; |
60 | let e0 = ((ix >> 23) - (0x7f + 23)) as i32; /* e0 = ilogb(|x|)-23, positive */ |
61 | tx[0] = f32::from_bits(ix - (e0 << 23) as u32) as f64; |
62 | let n = rem_pio2_large(&tx, &mut ty, e0, 0); |
63 | if sign { |
64 | return (-n, -ty[0]); |
65 | } |
66 | (n, ty[0]) |
67 | } |
68 | |