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 * ====================================================
15 * Return x mod y in exact arithmetic
16 * Method: shift and subtract
22 #include "math_private.h"
24 static const double one = 1.0, Zero[] = {0.0, -0.0,};
27 fmod(double x, double y)
29 int32_t n,hx,hy,hz,ix,iy,sx,i;
32 EXTRACT_WORDS(hx,lx,x);
33 EXTRACT_WORDS(hy,ly,y);
34 sx = hx&0x80000000; /* sign of x */
36 hy &= 0x7fffffff; /* |y| */
38 /* purge off exception values */
39 if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */
40 ((hy|((ly|-ly)>>31))>0x7ff00000)) /* or y is NaN */
43 if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */
45 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
48 /* determine ix = ilogb(x) */
49 if(hx<0x00100000) { /* subnormal x */
51 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
53 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
55 } else ix = (hx>>20)-1023;
57 /* determine iy = ilogb(y) */
58 if(hy<0x00100000) { /* subnormal y */
60 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
62 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
64 } else iy = (hy>>20)-1023;
66 /* set up {hx,lx}, {hy,ly} and align y to x */
68 hx = 0x00100000|(0x000fffff&hx);
69 else { /* subnormal x, shift x to normal */
72 hx = (hx<<n)|(lx>>(32-n));
80 hy = 0x00100000|(0x000fffff&hy);
81 else { /* subnormal y, shift y to normal */
84 hy = (hy<<n)|(ly>>(32-n));
95 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
96 if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
98 if((hz|lz)==0) /* return sign(x)*0 */
99 return Zero[(u_int32_t)sx>>31];
100 hx = hz+hz+(lz>>31); lx = lz+lz;
103 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
104 if(hz>=0) {hx=hz;lx=lz;}
106 /* convert back to floating value and restore the sign */
107 if((hx|lx)==0) /* return sign(x)*0 */
108 return Zero[(u_int32_t)sx>>31];
109 while(hx<0x00100000) { /* normalize x */
110 hx = hx+hx+(lx>>31); lx = lx+lx;
113 if(iy>= -1022) { /* normalize output */
114 hx = ((hx-0x00100000)|((iy+1023)<<20));
115 INSERT_WORDS(x,hx|sx,lx);
116 } else { /* subnormal output */
119 lx = (lx>>n)|((u_int32_t)hx<<(32-n));
122 lx = (hx<<(32-n))|(lx>>n); hx = sx;
124 lx = hx>>(n-32); hx = sx;
126 INSERT_WORDS(x,hx|sx,lx);
127 x *= one; /* create necessary signal */
129 return x; /* exact output */
132 #if LDBL_MANT_DIG == DBL_MANT_DIG
133 __strong_alias(fmodl, fmod);
134 #endif /* LDBL_MANT_DIG == DBL_MANT_DIG */