e_rem_pio2f.c revision 176552 
1/* e_rem_pio2f.c -- float version of e_rem_pio2.c
2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3 * Debugged and optimized by Bruce D. Evans.
4 */
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#include <sys/cdefs.h>
18__FBSDID("$FreeBSD: head/lib/msun/src/e_rem_pio2f.c 176552 2008-02-25 13:33:20Z bde $");
19
20/* __ieee754_rem_pio2f(x,y)
21 *
22 * return the remainder of x rem pi/2 in *y
23 * use double precision for everything except passing x
24 * use __kernel_rem_pio2() for large x
25 */
26
27#include <float.h>
28
29#include "math.h"
30#include "math_private.h"
31
32/*
33 * invpio2:  53 bits of 2/pi
34 * pio2_1:   first  33 bit of pi/2
35 * pio2_1t:  pi/2 - pio2_1
36 */
37
38static const double
39half =  5.00000000000000000000e-01, /* 0x3FE00000, 0x00000000 */
40invpio2 =  6.36619772367581382433e-01, /* 0x3FE45F30, 0x6DC9C883 */
41pio2_1  =  1.57079632673412561417e+00, /* 0x3FF921FB, 0x54400000 */
42pio2_1t =  6.07710050650619224932e-11; /* 0x3DD0B461, 0x1A626331 */
43
44int
45__ieee754_rem_pio2f(float x, double *y)
46{
47	double w,r,fn;
48	double tx[1];
49	float z;
50	int32_t e0,n,ix,hx;
51
52	GET_FLOAT_WORD(hx,x);
53	ix = hx&0x7fffffff;
54    /* 33+53 bit pi is good enough for medium size */
55	if(ix<=0x49490f80) {		/* |x| ~<= 2^19*(pi/2), medium size */
56	    /* Use a specialized rint() to get fn.  Assume round-to-nearest. */
57	    STRICT_ASSIGN(double,fn,x*invpio2+0x1.8p52);
58	    fn = fn-0x1.8p52;
59#ifdef HAVE_EFFICIENT_IRINT
60	    n  = irint(fn);
61#else
62	    n  = (int32_t)fn;
63#endif
64	    r  = x-fn*pio2_1;
65	    w  = fn*pio2_1t;
66	    *y = r-w;
67	    return n;
68	}
69    /*
70     * all other (large) arguments
71     */
72	if(ix>=0x7f800000) {		/* x is inf or NaN */
73	    *y=x-x; return 0;
74	}
75    /* set z = scalbn(|x|,ilogb(|x|)-23) */
76	e0 = (ix>>23)-150;		/* e0 = ilogb(|x|)-23; */
77	SET_FLOAT_WORD(z, ix - ((int32_t)(e0<<23)));
78	tx[0] = z;
79	n  =  __kernel_rem_pio2(tx,y,e0,1,0);
80	if(hx<0) {*y = -*y; return -n;}
81	return n;
82}
83