1 /* origin: FreeBSD /usr/src/lib/msun/src/e_rem_pio2f.c */
3 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
4 * Debugged and optimized by Bruce D. Evans.
7 * ====================================================
8 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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
14 * ====================================================
18 * return the remainder of x rem pi/2 in *y
19 * use double precision for everything except passing x
20 * use __rem_pio2_large() for large x
26 * invpio2: 53 bits of 2/pi
27 * pio2_1: first 25 bits of pi/2
28 * pio2_1t: pi/2 - pio2_1
31 invpio2 = 6.36619772367581382433e-01, /* 0x3FE45F30, 0x6DC9C883 */
32 pio2_1 = 1.57079631090164184570e+00, /* 0x3FF921FB, 0x50000000 */
33 pio2_1t = 1.58932547735281966916e-08; /* 0x3E5110b4, 0x611A6263 */
35 int __rem_pio2f(float x, double *y)
37 union {float f; uint32_t i;} u = {x};
38 double tx[1],ty[1],fn;
42 ix = u.i & 0x7fffffff;
43 /* 25+53 bit pi is good enough for medium size */
44 if (ix < 0x4dc90fdb) { /* |x| ~< 2^28*(pi/2), medium size */
45 /* Use a specialized rint() to get fn. Assume round-to-nearest. */
46 fn = x*invpio2 + 0x1.8p52;
49 *y = x - fn*pio2_1 - fn*pio2_1t;
52 if(ix>=0x7f800000) { /* x is inf or NaN */
56 /* scale x into [2^23, 2^24-1] */
58 e0 = (ix>>23) - (0x7f+23); /* e0 = ilogb(|x|)-23, positive */
61 n = __rem_pio2_large(tx,ty,e0,1,0);