e_rem_pio2f.c revision 176569 
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 176569 2008-02-25 22:19:17Z 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
44#ifdef INLINE_REM_PIO2F
45extern inline
46#endif
47int
48__ieee754_rem_pio2f(float x, double *y)
49{
50	double w,r,fn;
51	double tx[1],ty[1];
52	float z;
53	int32_t e0,n,ix,hx;
54
55	GET_FLOAT_WORD(hx,x);
56	ix = hx&0x7fffffff;
57    /* 33+53 bit pi is good enough for medium size */
58	if(ix<=0x49490f80) {		/* |x| ~<= 2^19*(pi/2), medium size */
59	    /* Use a specialized rint() to get fn.  Assume round-to-nearest. */
60	    STRICT_ASSIGN(double,fn,x*invpio2+0x1.8p52);
61	    fn = fn-0x1.8p52;
62#ifdef HAVE_EFFICIENT_IRINT
63	    n  = irint(fn);
64#else
65	    n  = (int32_t)fn;
66#endif
67	    r  = x-fn*pio2_1;
68	    w  = fn*pio2_1t;
69	    *y = r-w;
70	    return n;
71	}
72    /*
73     * all other (large) arguments
74     */
75	if(ix>=0x7f800000) {		/* x is inf or NaN */
76	    *y=x-x; return 0;
77	}
78    /* set z = scalbn(|x|,ilogb(|x|)-23) */
79	e0 = (ix>>23)-150;		/* e0 = ilogb(|x|)-23; */
80	SET_FLOAT_WORD(z, ix - ((int32_t)(e0<<23)));
81	tx[0] = z;
82	n  =  __kernel_rem_pio2(tx,ty,e0,1,0);
83	if(hx<0) {*y = -ty[0]; return -n;}
84	*y = ty[0]; return n;
85}
86