e_rem_pio2f.c revision 176356 
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#ifndef lint
18static char rcsid[] = "$FreeBSD: head/lib/msun/src/e_rem_pio2f.c 176356 2008-02-17 07:31:59Z das $";
19#endif
20
21/* __ieee754_rem_pio2f(x,y)
22 *
23 * return the remainder of x rem pi/2 in y[0]+y[1]
24 * use double precision internally
25 * use __kernel_rem_pio2() for large x
26 */
27
28#include "math.h"
29#include "math_private.h"
30
31/*
32 * invpio2:  53 bits of 2/pi
33 * pio2_1:   first  33 bit of pi/2
34 * pio2_1t:  pi/2 - pio2_1
35 */
36
37static const double
38zero =  0.00000000000000000000e+00, /* 0x00000000, 0x00000000 */
39half =  5.00000000000000000000e-01, /* 0x3FE00000, 0x00000000 */
40two24 =  1.67772160000000000000e+07, /* 0x41700000, 0x00000000 */
41invpio2 =  6.36619772367581382433e-01, /* 0x3FE45F30, 0x6DC9C883 */
42pio2_1  =  1.57079632673412561417e+00, /* 0x3FF921FB, 0x54400000 */
43pio2_1t =  6.07710050650619224932e-11; /* 0x3DD0B461, 0x1A626331 */
44
45	int32_t __ieee754_rem_pio2f(float x, float *y)
46{
47	double w,t,r,fn;
48	double tx[1],ty[2];
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	    t  = fabsf(x);
57	    n  = (int32_t) (t*invpio2+half);
58	    fn = (double)n;
59	    r  = t-fn*pio2_1;
60	    w  = fn*pio2_1t;
61	    y[0] = r-w;
62	    y[1] = (r-y[0])-w;
63	    if(hx<0) 	{y[0] = -y[0]; y[1] = -y[1]; return -n;}
64	    else	 return n;
65	}
66    /*
67     * all other (large) arguments
68     */
69	if(ix>=0x7f800000) {		/* x is inf or NaN */
70	    y[0]=y[1]=x-x; return 0;
71	}
72    /* set z = scalbn(|x|,ilogb(|x|)-23) */
73	e0 = (ix>>23)-150;		/* e0 = ilogb(|x|)-23; */
74	SET_FLOAT_WORD(z, ix - ((int32_t)(e0<<23)));
75	tx[0] = z;
76	n  =  __kernel_rem_pio2(tx,ty,e0,1,1);
77	y[0] = ty[0];
78	y[1] = ty[0] - y[0];
79	if(hx<0) {y[0] = -y[0]; y[1] = -y[1]; return -n;}
80	return n;
81}
82