1 /* @(#)e_fmod.c 1.3 95/01/18 */
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 #include <sys/cdefs.h>
14
15 #include "math.h"
16 #include "math_private.h"
17
18 static const float Zero[] = {0.0, -0.0,};
19
20 /*
21 * Return the IEEE remainder and set *quo to the last n bits of the
22 * quotient, rounded to the nearest integer. We choose n=31 because
23 * we wind up computing all the integer bits of the quotient anyway as
24 * a side-effect of computing the remainder by the shift and subtract
25 * method. In practice, this is far more bits than are needed to use
26 * remquo in reduction algorithms.
27 */
28 float
remquof(float x,float y,int * quo)29 remquof(float x, float y, int *quo)
30 {
31 int32_t n,hx,hy,hz,ix,iy,sx,i;
32 u_int32_t q,sxy;
33
34 GET_FLOAT_WORD(hx,x);
35 GET_FLOAT_WORD(hy,y);
36 sxy = (hx ^ hy) & 0x80000000;
37 sx = hx&0x80000000; /* sign of x */
38 hx ^=sx; /* |x| */
39 hy &= 0x7fffffff; /* |y| */
40
41 /* purge off exception values */
42 if(hy==0||hx>=0x7f800000||hy>0x7f800000) /* y=0,NaN;or x not finite */
43 return (x*y)/(x*y);
44 if(hx<hy) {
45 q = 0;
46 goto fixup; /* |x|<|y| return x or x-y */
47 } else if(hx==hy) {
48 *quo = 1;
49 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
50 }
51
52 /* determine ix = ilogb(x) */
53 if(hx<0x00800000) { /* subnormal x */
54 for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
55 } else ix = (hx>>23)-127;
56
57 /* determine iy = ilogb(y) */
58 if(hy<0x00800000) { /* subnormal y */
59 for (iy = -126,i=(hy<<8); i>0; i<<=1) iy -=1;
60 } else iy = (hy>>23)-127;
61
62 /* set up {hx,lx}, {hy,ly} and align y to x */
63 if(ix >= -126)
64 hx = 0x00800000|(0x007fffff&hx);
65 else { /* subnormal x, shift x to normal */
66 n = -126-ix;
67 hx <<= n;
68 }
69 if(iy >= -126)
70 hy = 0x00800000|(0x007fffff&hy);
71 else { /* subnormal y, shift y to normal */
72 n = -126-iy;
73 hy <<= n;
74 }
75
76 /* fix point fmod */
77 n = ix - iy;
78 q = 0;
79 while(n--) {
80 hz=hx-hy;
81 if(hz<0) hx = hx << 1;
82 else {hx = hz << 1; q++;}
83 q <<= 1;
84 }
85 hz=hx-hy;
86 if(hz>=0) {hx=hz;q++;}
87
88 /* convert back to floating value and restore the sign */
89 if(hx==0) { /* return sign(x)*0 */
90 *quo = (sxy ? -q : q);
91 return Zero[(u_int32_t)sx>>31];
92 }
93 while(hx<0x00800000) { /* normalize x */
94 hx <<= 1;
95 iy -= 1;
96 }
97 if(iy>= -126) { /* normalize output */
98 hx = ((hx-0x00800000)|((iy+127)<<23));
99 } else { /* subnormal output */
100 n = -126 - iy;
101 hx >>= n;
102 }
103 fixup:
104 SET_FLOAT_WORD(x,hx);
105 y = fabsf(y);
106 if (y < 0x1p-125f) {
107 if (x+x>y || (x+x==y && (q & 1))) {
108 q++;
109 x-=y;
110 }
111 } else if (x>0.5f*y || (x==0.5f*y && (q & 1))) {
112 q++;
113 x-=y;
114 }
115 GET_FLOAT_WORD(hx,x);
116 SET_FLOAT_WORD(x,hx^sx);
117 q &= 0x7fffffff;
118 *quo = (sxy ? -q : q);
119 return x;
120 }
121