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The Android Open Source Project1dc9e472009-03-03 19:28:35 -08001
2/* @(#)e_fmod.c 1.3 95/01/18 */
3/*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
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
10 * is preserved.
11 * ====================================================
12 */
13
14#ifndef lint
15static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_fmod.c,v 1.9 2005/02/04 18:26:05 das Exp $";
16#endif
17
18/*
19 * __ieee754_fmod(x,y)
20 * Return x mod y in exact arithmetic
21 * Method: shift and subtract
22 */
23
24#include "math.h"
25#include "math_private.h"
26
27static const double one = 1.0, Zero[] = {0.0, -0.0,};
28
29double
30__ieee754_fmod(double x, double y)
31{
32 int32_t n,hx,hy,hz,ix,iy,sx,i;
33 u_int32_t lx,ly,lz;
34
35 EXTRACT_WORDS(hx,lx,x);
36 EXTRACT_WORDS(hy,ly,y);
37 sx = hx&0x80000000; /* sign of x */
38 hx ^=sx; /* |x| */
39 hy &= 0x7fffffff; /* |y| */
40
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 */
44 return (x*y)/(x*y);
45 if(hx<=hy) {
46 if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */
47 if(lx==ly)
48 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
49 }
50
51 /* determine ix = ilogb(x) */
52 if(hx<0x00100000) { /* subnormal x */
53 if(hx==0) {
54 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
55 } else {
56 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
57 }
58 } else ix = (hx>>20)-1023;
59
60 /* determine iy = ilogb(y) */
61 if(hy<0x00100000) { /* subnormal y */
62 if(hy==0) {
63 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
64 } else {
65 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
66 }
67 } else iy = (hy>>20)-1023;
68
69 /* set up {hx,lx}, {hy,ly} and align y to x */
70 if(ix >= -1022)
71 hx = 0x00100000|(0x000fffff&hx);
72 else { /* subnormal x, shift x to normal */
73 n = -1022-ix;
74 if(n<=31) {
75 hx = (hx<<n)|(lx>>(32-n));
76 lx <<= n;
77 } else {
78 hx = lx<<(n-32);
79 lx = 0;
80 }
81 }
82 if(iy >= -1022)
83 hy = 0x00100000|(0x000fffff&hy);
84 else { /* subnormal y, shift y to normal */
85 n = -1022-iy;
86 if(n<=31) {
87 hy = (hy<<n)|(ly>>(32-n));
88 ly <<= n;
89 } else {
90 hy = ly<<(n-32);
91 ly = 0;
92 }
93 }
94
95 /* fix point fmod */
96 n = ix - iy;
97 while(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;}
100 else {
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;
104 }
105 }
106 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
107 if(hz>=0) {hx=hz;lx=lz;}
108
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;
114 iy -= 1;
115 }
116 if(iy>= -1022) { /* normalize output */
117 hx = ((hx-0x00100000)|((iy+1023)<<20));
118 INSERT_WORDS(x,hx|sx,lx);
119 } else { /* subnormal output */
120 n = -1022 - iy;
121 if(n<=20) {
122 lx = (lx>>n)|((u_int32_t)hx<<(32-n));
123 hx >>= n;
124 } else if (n<=31) {
125 lx = (hx<<(32-n))|(lx>>n); hx = sx;
126 } else {
127 lx = hx>>(n-32); hx = sx;
128 }
129 INSERT_WORDS(x,hx|sx,lx);
130 x *= one; /* create necessary signal */
131 }
132 return x; /* exact output */
133}