1 /* @(#)e_fmod.c 5.1 93/09/24 */
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
10 * ====================================================
12 * $NetBSD: e_fmod.c,v 1.11 2002/05/26 22:01:49 wiz Exp $
13 * $DragonFly: src/lib/libm/src/e_fmod.c,v 1.1 2005/07/26 21:15:20 joerg Exp $
18 * Return x mod y in exact arithmetic
19 * Method: shift and subtract
23 #include "math_private.h"
25 static const double one = 1.0, Zero[] = {0.0, -0.0,};
28 fmod(double x, double y)
30 int32_t n,hx,hy,hz,ix,iy,sx,i;
33 EXTRACT_WORDS(hx,lx,x);
34 EXTRACT_WORDS(hy,ly,y);
35 sx = hx&0x80000000; /* sign of x */
37 hy &= 0x7fffffff; /* |y| */
39 /* purge off exception values */
40 if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */
41 ((hy|((ly|-ly)>>31))>0x7ff00000)) /* or y is NaN */
44 if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */
46 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
49 /* determine ix = ilogb(x) */
50 if(hx<0x00100000) { /* subnormal x */
52 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
54 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
56 } else ix = (hx>>20)-1023;
58 /* determine iy = ilogb(y) */
59 if(hy<0x00100000) { /* subnormal y */
61 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
63 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
65 } else iy = (hy>>20)-1023;
67 /* set up {hx,lx}, {hy,ly} and align y to x */
69 hx = 0x00100000|(0x000fffff&hx);
70 else { /* subnormal x, shift x to normal */
73 hx = (hx<<n)|(lx>>(32-n));
81 hy = 0x00100000|(0x000fffff&hy);
82 else { /* subnormal y, shift y to normal */
85 hy = (hy<<n)|(ly>>(32-n));
96 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
97 if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
99 if((hz|lz)==0) /* return sign(x)*0 */
100 return Zero[(u_int32_t)sx>>31];
101 hx = hz+hz+(lz>>31); lx = lz+lz;
104 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
105 if(hz>=0) {hx=hz;lx=lz;}
107 /* convert back to floating value and restore the sign */
108 if((hx|lx)==0) /* return sign(x)*0 */
109 return Zero[(u_int32_t)sx>>31];
110 while(hx<0x00100000) { /* normalize x */
111 hx = hx+hx+(lx>>31); lx = lx+lx;
114 if(iy>= -1022) { /* normalize output */
115 hx = ((hx-0x00100000)|((iy+1023)<<20));
116 INSERT_WORDS(x,hx|sx,lx);
117 } else { /* subnormal output */
120 lx = (lx>>n)|((u_int32_t)hx<<(32-n));
123 lx = (hx<<(32-n))|(lx>>n); hx = sx;
125 lx = hx>>(n-32); hx = sx;
127 INSERT_WORDS(x,hx|sx,lx);
128 x *= one; /* create necessary signal */
130 return x; /* exact output */