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[glibc.git] / sysdeps / libm-ieee754 / e_fmod.c
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1 /* @(#)e_fmod.c 5.1 93/09/24 */
2 /*
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
9 * is preserved.
10 * ====================================================
13 #if defined(LIBM_SCCS) && !defined(lint)
14 static char rcsid[] = "$NetBSD: e_fmod.c,v 1.8 1995/05/10 20:45:07 jtc Exp $";
15 #endif
17 /*
18 * __ieee754_fmod(x,y)
19 * Return x mod y in exact arithmetic
20 * Method: shift and subtract
23 #include "math.h"
24 #include "math_private.h"
26 #ifdef __STDC__
27 static const double one = 1.0, Zero[] = {0.0, -0.0,};
28 #else
29 static double one = 1.0, Zero[] = {0.0, -0.0,};
30 #endif
32 #ifdef __STDC__
33 double __ieee754_fmod(double x, double y)
34 #else
35 double __ieee754_fmod(x,y)
36 double x,y ;
37 #endif
39 int32_t n,hx,hy,hz,ix,iy,sx,i;
40 u_int32_t lx,ly,lz;
42 EXTRACT_WORDS(hx,lx,x);
43 EXTRACT_WORDS(hy,ly,y);
44 sx = hx&0x80000000; /* sign of x */
45 hx ^=sx; /* |x| */
46 hy &= 0x7fffffff; /* |y| */
48 /* purge off exception values */
49 if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */
50 ((hy|((ly|-ly)>>31))>0x7ff00000)) /* or y is NaN */
51 return (x*y)/(x*y);
52 if(hx<=hy) {
53 if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */
54 if(lx==ly)
55 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
58 /* determine ix = ilogb(x) */
59 if(hx<0x00100000) { /* subnormal x */
60 if(hx==0) {
61 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
62 } else {
63 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
65 } else ix = (hx>>20)-1023;
67 /* determine iy = ilogb(y) */
68 if(hy<0x00100000) { /* subnormal y */
69 if(hy==0) {
70 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
71 } else {
72 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
74 } else iy = (hy>>20)-1023;
76 /* set up {hx,lx}, {hy,ly} and align y to x */
77 if(ix >= -1022)
78 hx = 0x00100000|(0x000fffff&hx);
79 else { /* subnormal x, shift x to normal */
80 n = -1022-ix;
81 if(n<=31) {
82 hx = (hx<<n)|(lx>>(32-n));
83 lx <<= n;
84 } else {
85 hx = lx<<(n-32);
86 lx = 0;
89 if(iy >= -1022)
90 hy = 0x00100000|(0x000fffff&hy);
91 else { /* subnormal y, shift y to normal */
92 n = -1022-iy;
93 if(n<=31) {
94 hy = (hy<<n)|(ly>>(32-n));
95 ly <<= n;
96 } else {
97 hy = ly<<(n-32);
98 ly = 0;
102 /* fix point fmod */
103 n = ix - iy;
104 while(n--) {
105 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
106 if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
107 else {
108 if((hz|lz)==0) /* return sign(x)*0 */
109 return Zero[(u_int32_t)sx>>31];
110 hx = hz+hz+(lz>>31); lx = lz+lz;
113 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
114 if(hz>=0) {hx=hz;lx=lz;}
116 /* convert back to floating value and restore the sign */
117 if((hx|lx)==0) /* return sign(x)*0 */
118 return Zero[(u_int32_t)sx>>31];
119 while(hx<0x00100000) { /* normalize x */
120 hx = hx+hx+(lx>>31); lx = lx+lx;
121 iy -= 1;
123 if(iy>= -1022) { /* normalize output */
124 hx = ((hx-0x00100000)|((iy+1023)<<20));
125 INSERT_WORDS(x,hx|sx,lx);
126 } else { /* subnormal output */
127 n = -1022 - iy;
128 if(n<=20) {
129 lx = (lx>>n)|((u_int32_t)hx<<(32-n));
130 hx >>= n;
131 } else if (n<=31) {
132 lx = (hx<<(32-n))|(lx>>n); hx = sx;
133 } else {
134 lx = hx>>(n-32); hx = sx;
136 INSERT_WORDS(x,hx|sx,lx);
137 x *= one; /* create necessary signal */
139 return x; /* exact output */