2 /* @(#)e_fmod.c 1.3 95/01/18 */
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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
11 * ====================================================
15 static char rcsid[] = "$FreeBSD$";
20 * Return x mod y in exact arithmetic
21 * Method: shift and subtract
25 #include "math_private.h"
27 static const double one = 1.0, Zero[] = {0.0, -0.0,};
30 __ieee754_fmod(double x, double y)
32 int32_t n,hx,hy,hz,ix,iy,sx,i;
35 EXTRACT_WORDS(hx,lx,x);
36 EXTRACT_WORDS(hy,ly,y);
37 sx = hx&0x80000000; /* sign of x */
39 hy &= 0x7fffffff; /* |y| */
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 */
46 if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */
48 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
51 /* determine ix = ilogb(x) */
52 if(hx<0x00100000) { /* subnormal x */
54 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
56 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
58 } else ix = (hx>>20)-1023;
60 /* determine iy = ilogb(y) */
61 if(hy<0x00100000) { /* subnormal y */
63 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
65 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
67 } else iy = (hy>>20)-1023;
69 /* set up {hx,lx}, {hy,ly} and align y to x */
71 hx = 0x00100000|(0x000fffff&hx);
72 else { /* subnormal x, shift x to normal */
75 hx = (hx<<n)|(lx>>(32-n));
83 hy = 0x00100000|(0x000fffff&hy);
84 else { /* subnormal y, shift y to normal */
87 hy = (hy<<n)|(ly>>(32-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;}
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;
106 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
107 if(hz>=0) {hx=hz;lx=lz;}
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;
116 if(iy>= -1022) { /* normalize output */
117 hx = ((hx-0x00100000)|((iy+1023)<<20));
118 INSERT_WORDS(x,hx|sx,lx);
119 } else { /* subnormal output */
122 lx = (lx>>n)|((u_int32_t)hx<<(32-n));
125 lx = (hx<<(32-n))|(lx>>n); hx = sx;
127 lx = hx>>(n-32); hx = sx;
129 INSERT_WORDS(x,hx|sx,lx);
130 x *= one; /* create necessary signal */
132 return x; /* exact output */