1
2 /*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunSoft, 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 /*
14 * fmod(x,y)
15 * Return x mod y in exact arithmetic
16 * Method: shift and subtract
17 */
18
19 #include <float.h>
20
21 #include "math.h"
22 #include "math_private.h"
23
24 static const double one = 1.0, Zero[] = {0.0, -0.0,};
25
26 double
fmod(double x,double y)27 fmod(double x, double y)
28 {
29 int32_t hx, hy, hz, ix, iy, n, sx;
30 u_int32_t lx, ly, lz;
31
32 EXTRACT_WORDS(hx,lx,x);
33 EXTRACT_WORDS(hy,ly,y);
34 sx = hx&0x80000000; /* sign of x */
35 hx ^= sx; /* |x| */
36 hy &= 0x7fffffff; /* |y| */
37
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 */
41 return nan_mix_op(x, y, *)/nan_mix_op(x, y, *);
42 if(hx<=hy) {
43 if((hx<hy)||(lx<ly)) return x; /* |x|<|y| return x */
44 if(lx==ly)
45 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
46 }
47
48 /* determine ix = ilogb(x) */
49 if(hx<0x00100000)
50 ix = subnormal_ilogb(hx, lx);
51 else
52 ix = (hx>>20)-1023;
53
54 /* determine iy = ilogb(y) */
55 if(hy<0x00100000)
56 iy = subnormal_ilogb(hy, ly);
57 else
58 iy = (hy>>20)-1023;
59
60 /* set up {hx,lx}, {hy,ly} and align y to x */
61 if(ix >= -1022)
62 hx = 0x00100000|(0x000fffff&hx);
63 else { /* subnormal x, shift x to normal */
64 n = -1022-ix;
65 if(n<=31) {
66 hx = (hx<<n)|(lx>>(32-n));
67 lx <<= n;
68 } else {
69 hx = lx<<(n-32);
70 lx = 0;
71 }
72 }
73 if(iy >= -1022)
74 hy = 0x00100000|(0x000fffff&hy);
75 else { /* subnormal y, shift y to normal */
76 n = -1022-iy;
77 if(n<=31) {
78 hy = (hy<<n)|(ly>>(32-n));
79 ly <<= n;
80 } else {
81 hy = ly<<(n-32);
82 ly = 0;
83 }
84 }
85
86 /* fix point fmod */
87 n = ix - iy;
88 while(n--) {
89 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
90 if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
91 else {
92 if((hz|lz)==0) /* return sign(x)*0 */
93 return Zero[(u_int32_t)sx>>31];
94 hx = hz+hz+(lz>>31); lx = lz+lz;
95 }
96 }
97 hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
98 if(hz>=0) {hx=hz;lx=lz;}
99
100 /* convert back to floating value and restore the sign */
101 if((hx|lx)==0) /* return sign(x)*0 */
102 return Zero[(u_int32_t)sx>>31];
103 while(hx<0x00100000) { /* normalize x */
104 hx = hx+hx+(lx>>31); lx = lx+lx;
105 iy -= 1;
106 }
107 if(iy>= -1022) { /* normalize output */
108 hx = ((hx-0x00100000)|((iy+1023)<<20));
109 INSERT_WORDS(x,hx|sx,lx);
110 } else { /* subnormal output */
111 n = -1022 - iy;
112 if(n<=20) {
113 lx = (lx>>n)|((u_int32_t)hx<<(32-n));
114 hx >>= n;
115 } else if (n<=31) {
116 lx = (hx<<(32-n))|(lx>>n); hx = sx;
117 } else {
118 lx = hx>>(n-32); hx = sx;
119 }
120 INSERT_WORDS(x,hx|sx,lx);
121 x *= one; /* create necessary signal */
122 }
123 return x; /* exact output */
124 }
125
126 #if (LDBL_MANT_DIG == 53)
127 __weak_reference(fmod, fmodl);
128 #endif
129