e_fmod.c revision a27d2baa0c1a2ec70f47ea9199b1dd6762c8a349 
1
2/* @(#)e_fmod.c 1.3 95/01/18 */
3/*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 */
13
14#ifndef lint
15static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_fmod.c,v 1.9 2005/02/04 18:26:05 das Exp $";
16#endif
17
18/*
19 * __ieee754_fmod(x,y)
20 * Return x mod y in exact arithmetic
21 * Method: shift and subtract
22 */
23
24#include "math.h"
25#include "math_private.h"
26
27static const double one = 1.0, Zero[] = {0.0, -0.0,};
28
29double
30__ieee754_fmod(double x, double y)
31{
32	int32_t n,hx,hy,hz,ix,iy,sx,i;
33	u_int32_t lx,ly,lz;
34
35	EXTRACT_WORDS(hx,lx,x);
36	EXTRACT_WORDS(hy,ly,y);
37	sx = hx&0x80000000;		/* sign of x */
38	hx ^=sx;		/* |x| */
39	hy &= 0x7fffffff;	/* |y| */
40
41    /* purge off exception values */
42	if((hy|ly)==0||(hx>=0x7ff00000)||	/* y=0,or x not finite */
43	  ((hy|((ly|-ly)>>31))>0x7ff00000))	/* or y is NaN */
44	    return (x*y)/(x*y);
45	if(hx<=hy) {
46	    if((hx<hy)||(lx<ly)) return x;	/* |x|<|y| return x */
47	    if(lx==ly)
48		return Zero[(u_int32_t)sx>>31];	/* |x|=|y| return x*0*/
49	}
50
51    /* determine ix = ilogb(x) */
52	if(hx<0x00100000) {	/* subnormal x */
53	    if(hx==0) {
54		for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
55	    } else {
56		for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
57	    }
58	} else ix = (hx>>20)-1023;
59
60    /* determine iy = ilogb(y) */
61	if(hy<0x00100000) {	/* subnormal y */
62	    if(hy==0) {
63		for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
64	    } else {
65		for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
66	    }
67	} else iy = (hy>>20)-1023;
68
69    /* set up {hx,lx}, {hy,ly} and align y to x */
70	if(ix >= -1022)
71	    hx = 0x00100000|(0x000fffff&hx);
72	else {		/* subnormal x, shift x to normal */
73	    n = -1022-ix;
74	    if(n<=31) {
75	        hx = (hx<<n)|(lx>>(32-n));
76	        lx <<= n;
77	    } else {
78		hx = lx<<(n-32);
79		lx = 0;
80	    }
81	}
82	if(iy >= -1022)
83	    hy = 0x00100000|(0x000fffff&hy);
84	else {		/* subnormal y, shift y to normal */
85	    n = -1022-iy;
86	    if(n<=31) {
87	        hy = (hy<<n)|(ly>>(32-n));
88	        ly <<= n;
89	    } else {
90		hy = ly<<(n-32);
91		ly = 0;
92	    }
93	}
94
95    /* fix point fmod */
96	n = ix - iy;
97	while(n--) {
98	    hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
99	    if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
100	    else {
101	    	if((hz|lz)==0) 		/* return sign(x)*0 */
102		    return Zero[(u_int32_t)sx>>31];
103	    	hx = hz+hz+(lz>>31); lx = lz+lz;
104	    }
105	}
106	hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
107	if(hz>=0) {hx=hz;lx=lz;}
108
109    /* convert back to floating value and restore the sign */
110	if((hx|lx)==0) 			/* return sign(x)*0 */
111	    return Zero[(u_int32_t)sx>>31];
112	while(hx<0x00100000) {		/* normalize x */
113	    hx = hx+hx+(lx>>31); lx = lx+lx;
114	    iy -= 1;
115	}
116	if(iy>= -1022) {	/* normalize output */
117	    hx = ((hx-0x00100000)|((iy+1023)<<20));
118	    INSERT_WORDS(x,hx|sx,lx);
119	} else {		/* subnormal output */
120	    n = -1022 - iy;
121	    if(n<=20) {
122		lx = (lx>>n)|((u_int32_t)hx<<(32-n));
123		hx >>= n;
124	    } else if (n<=31) {
125		lx = (hx<<(32-n))|(lx>>n); hx = sx;
126	    } else {
127		lx = hx>>(n-32); hx = sx;
128	    }
129	    INSERT_WORDS(x,hx|sx,lx);
130	    x *= one;		/* create necessary signal */
131	}
132	return x;		/* exact output */
133}
134