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