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 /* __FBSDID("$FreeBSD: src/lib/msun/src/s_remquof.c,v 1.1 2005/03/25 04:40:44 das Exp $"); */
15
16 #include "math.h"
17 #include "math_private.h"
18
19 static const float Zero[] = {0.0, -0.0,};
20
21 /*
22 * Return the IEEE remainder and set *quo to the last n bits of the
23 * quotient, rounded to the nearest integer. We choose n=31 because
24 * we wind up computing all the integer bits of the quotient anyway as
25 * a side-effect of computing the remainder by the shift and subtract
26 * method. In practice, this is far more bits than are needed to use
27 * remquo in reduction algorithms.
28 */
29 float
remquof(float x,float y,int * quo)30 remquof(float x, float y, int *quo)
31 {
32 int32_t n,hx,hy,hz,ix,iy,sx,i;
33 u_int32_t q,sxy;
34
35 GET_FLOAT_WORD(hx,x);
36 GET_FLOAT_WORD(hy,y);
37 sxy = (hx ^ hy) & 0x80000000;
38 sx = hx&0x80000000; /* sign of x */
39 hx ^=sx; /* |x| */
40 hy &= 0x7fffffff; /* |y| */
41
42 /* purge off exception values */
43 if(hy==0||hx>=0x7f800000||hy>0x7f800000) /* y=0,NaN;or x not finite */
44 return (x*y)/(x*y);
45 if(hx<hy) {
46 q = 0;
47 goto fixup; /* |x|<|y| return x or x-y */
48 } else if(hx==hy) {
49 *quo = (sxy ? -1 : 1);
50 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
51 }
52
53 /* determine ix = ilogb(x) */
54 if(hx<0x00800000) { /* subnormal x */
55 for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
56 } else ix = (hx>>23)-127;
57
58 /* determine iy = ilogb(y) */
59 if(hy<0x00800000) { /* subnormal y */
60 for (iy = -126,i=(hy<<8); i>0; i<<=1) iy -=1;
61 } else iy = (hy>>23)-127;
62
63 /* set up {hx,lx}, {hy,ly} and align y to x */
64 if(ix >= -126)
65 hx = 0x00800000|(0x007fffff&hx);
66 else { /* subnormal x, shift x to normal */
67 n = -126-ix;
68 hx <<= n;
69 }
70 if(iy >= -126)
71 hy = 0x00800000|(0x007fffff&hy);
72 else { /* subnormal y, shift y to normal */
73 n = -126-iy;
74 hy <<= n;
75 }
76
77 /* fix point fmod */
78 n = ix - iy;
79 q = 0;
80 while(n--) {
81 hz=hx-hy;
82 if(hz<0) hx = hx << 1;
83 else {hx = hz << 1; q++;}
84 q <<= 1;
85 }
86 hz=hx-hy;
87 if(hz>=0) {hx=hz;q++;}
88
89 /* convert back to floating value and restore the sign */
90 if(hx==0) { /* return sign(x)*0 */
91 q &= 0x7fffffff;
92 *quo = (sxy ? -q : q);
93 return Zero[(u_int32_t)sx>>31];
94 }
95 while(hx<0x00800000) { /* normalize x */
96 hx <<= 1;
97 iy -= 1;
98 }
99 if(iy>= -126) { /* normalize output */
100 hx = ((hx-0x00800000)|((iy+127)<<23));
101 } else { /* subnormal output */
102 n = -126 - iy;
103 hx >>= n;
104 }
105 fixup:
106 SET_FLOAT_WORD(x,hx);
107 y = fabsf(y);
108 if (y < 0x1p-125f) {
109 if (x+x>y || (x+x==y && (q & 1))) {
110 q++;
111 x-=y;
112 }
113 } else if (x>0.5f*y || (x==0.5f*y && (q & 1))) {
114 q++;
115 x-=y;
116 }
117 GET_FLOAT_WORD(hx,x);
118 SET_FLOAT_WORD(x,hx^sx);
119 q &= 0x7fffffff;
120 *quo = (sxy ? -q : q);
121 return x;
122 }
123