1 /*
2 * ====================================================
3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4 *
5 * Developed at SunPro, a Sun Microsystems, Inc. business.
6 * Permission to use, copy, modify, and distribute this
7 * software is freely granted, provided that this notice
8 * is preserved.
9 * ====================================================
10 */
11
12 /*
13 * __ieee754_fmod(x,y)
14 * Return x mod y in exact arithmetic
15 * Method: shift and subtract
16 */
17
18 #include "bsd_private.h"
19
bsd__ieee754_fmod(double x,double y)20 double bsd__ieee754_fmod(double x, double y)
21 {
22 int32_t n,hx,hy,hz,ix,iy,sx,i;
23 u_int32_t lx,ly,lz;
24
25 EXTRACT_WORDS(hx,lx,x);
26 EXTRACT_WORDS(hy,ly,y);
27 sx = hx&0x80000000; /* sign of x */
28 hx ^=sx; /* |x| */
29 hy &= 0x7fffffff; /* |y| */
30
31 /* purge off exception values */
32 if((hy|ly)==0||(hx>=0x7ff00000)|| /* y=0,or x not finite */
33 ((hy|((ly|-ly)>>31))>0x7ff00000)) /* or y is NaN */
34 return (x*y)/(x*y);
35 if(hx<=hy) {
36 if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */
37 if(lx==ly)
38 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
39 }
40
41 /* determine ix = ilogb(x) */
42 if(hx<0x00100000) { /* subnormal x */
43 if(hx==0) {
44 for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
45 } else {
46 for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
47 }
48 } else ix = (hx>>20)-1023;
49
50 /* determine iy = ilogb(y) */
51 if(hy<0x00100000) { /* subnormal y */
52 if(hy==0) {
53 for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
54 } else {
55 for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
56 }
57 } else iy = (hy>>20)-1023;
58
59 /* set up {hx,lx}, {hy,ly} and align y to x */
60 if(ix >= -1022)
61 hx = 0x00100000|(0x000fffff&hx);
62 else { /* subnormal x, shift x to normal */
63 n = -1022-ix;
64 if(n<=31) {
65 hx = (hx<<n)|(lx>>(32-n));
66 lx <<= n;
67 } else {
68 hx = lx<<(n-32);
69 lx = 0;
70 }
71 }
72 if(iy >= -1022)
73 hy = 0x00100000|(0x000fffff&hy);
74 else { /* subnormal y, shift y to normal */
75 n = -1022-iy;
76 if(n<=31) {
77 hy = (hy<<n)|(ly>>(32-n));
78 ly <<= n;
79 } else {
80 hy = ly<<(n-32);
81 ly = 0;
82 }
83 }
84
85 /* fix point fmod */
86 n = ix - iy;
87 while(n--) {
88 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
89 if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
90 else {
91 if((hz|lz)==0) /* return sign(x)*0 */
92 return Zero[(u_int32_t)sx>>31];
93 hx = hz+hz+(lz>>31); lx = lz+lz;
94 }
95 }
96 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
97 if(hz>=0) {hx=hz;lx=lz;}
98
99 /* convert back to floating value and restore the sign */
100 if((hx|lx)==0) /* return sign(x)*0 */
101 return Zero[(u_int32_t)sx>>31];
102 while(hx<0x00100000) { /* normalize x */
103 hx = hx+hx+(lx>>31); lx = lx+lx;
104 iy -= 1;
105 }
106 if(iy>= -1022) { /* normalize output */
107 hx = ((hx-0x00100000)|((iy+1023)<<20));
108 INSERT_WORDS(x,hx|sx,lx);
109 } else { /* subnormal output */
110 n = -1022 - iy;
111 if(n<=20) {
112 lx = (lx>>n)|((u_int32_t)hx<<(32-n));
113 hx >>= n;
114 } else if (n<=31) {
115 lx = (hx<<(32-n))|(lx>>n); hx = sx;
116 } else {
117 lx = hx>>(n-32); hx = sx;
118 }
119 INSERT_WORDS(x,hx|sx,lx);
120 x *= one; /* create necessary signal */
121 }
122 return x; /* exact output */
123 }
124