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---
e_fmod.c (3370B)
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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.
5 *
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 * ====================================================
11 */
12
13 #ifndef lint
14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_fmod.c,v 1.8 2003/07/23 04:53:46 peter Exp $";
15 #endif
16
17 /*
18 * __ieee754_fmod(x,y)
19 * Return x mod y in exact arithmetic
20 * Method: shift and subtract
21 */
22
23 #include "math.h"
24 #include "math_private.h"
25
26 static const double one = 1.0, Zero[] = {0.0, -0.0,};
27
28 double
29 __ieee754_fmod(double x, double y)
30 {
31 int32_t n,hx,hy,hz,ix,iy,sx,i;
32 u_int32_t lx,ly,lz;
33
34 EXTRACT_WORDS(hx,lx,x);
35 EXTRACT_WORDS(hy,ly,y);
36 sx = hx&0x80000000; /* sign of x */
37 hx ^=sx; /* |x| */
38 hy &= 0x7fffffff; /* |y| */
39
40 /* purge off exception values */
41 if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */
42 ((hy|((ly|-ly)>>31))>0x7ff00000)) /* or y is NaN */
43 return (x*y)/(x*y);
44 if(hx<=hy) {
45 if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */
46 if(lx==ly)
47 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
48 }
49
50 /* determine ix = ilogb(x) */
51 if(hx<0x00100000) { /* subnormal x */
52 if(hx==0) {
53 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
54 } else {
55 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
56 }
57 } else ix = (hx>>20)-1023;
58
59 /* determine iy = ilogb(y) */
60 if(hy<0x00100000) { /* subnormal y */
61 if(hy==0) {
62 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
63 } else {
64 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
65 }
66 } else iy = (hy>>20)-1023;
67
68 /* set up {hx,lx}, {hy,ly} and align y to x */
69 if(ix >= -1022)
70 hx = 0x00100000|(0x000fffff&hx);
71 else { /* subnormal x, shift x to normal */
72 n = -1022-ix;
73 if(n<=31) {
74 hx = (hx<<n)|(lx>>(32-n));
75 lx <<= n;
76 } else {
77 hx = lx<<(n-32);
78 lx = 0;
79 }
80 }
81 if(iy >= -1022)
82 hy = 0x00100000|(0x000fffff&hy);
83 else { /* subnormal y, shift y to normal */
84 n = -1022-iy;
85 if(n<=31) {
86 hy = (hy<<n)|(ly>>(32-n));
87 ly <<= n;
88 } else {
89 hy = ly<<(n-32);
90 ly = 0;
91 }
92 }
93
94 /* fix point fmod */
95 n = ix - iy;
96 while(n--) {
97 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
98 if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
99 else {
100 if((hz|lz)==0) /* return sign(x)*0 */
101 return Zero[(u_int32_t)sx>>31];
102 hx = hz+hz+(lz>>31); lx = lz+lz;
103 }
104 }
105 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
106 if(hz>=0) {hx=hz;lx=lz;}
107
108 /* convert back to floating value and restore the sign */
109 if((hx|lx)==0) /* return sign(x)*0 */
110 return Zero[(u_int32_t)sx>>31];
111 while(hx<0x00100000) { /* normalize x */
112 hx = hx+hx+(lx>>31); lx = lx+lx;
113 iy -= 1;
114 }
115 if(iy>= -1022) { /* normalize output */
116 hx = ((hx-0x00100000)|((iy+1023)<<20));
117 INSERT_WORDS(x,hx|sx,lx);
118 } else { /* subnormal output */
119 n = -1022 - iy;
120 if(n<=20) {
121 lx = (lx>>n)|((u_int32_t)hx<<(32-n));
122 hx >>= n;
123 } else if (n<=31) {
124 lx = (hx<<(32-n))|(lx>>n); hx = sx;
125 } else {
126 lx = hx>>(n-32); hx = sx;
127 }
128 INSERT_WORDS(x,hx|sx,lx);
129 x *= one; /* create necessary signal */
130 }
131 return x; /* exact output */
132 }