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
17use core::f64;
18
19use super::rem_pio2_large;
20
21const TOINT: f64 = 1.5 / f64::EPSILON;
22
23/// 53 bits of 2/pi
24const INV_PIO2: f64 = 6.36619772367581382433e-01; /* 0x3FE45F30, 0x6DC9C883 */
25/// first 25 bits of pi/2
26const PIO2_1: f64 = 1.57079631090164184570e+00; /* 0x3FF921FB, 0x50000000 */
27/// pi/2 - pio2_1
28const 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)]
35pub(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