1 /*-
2 * ====================================================
3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4 *
5 * Developed at SunSoft, 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 #include "math.h"
13 #include "math_private.h"
14
15 static const float Zero[] = {0.0, -0.0,};
16
17 /*
18 * Return the IEEE remainder and set *quo to the last n bits of the
19 * quotient, rounded to the nearest integer. We choose n=31 because
20 * we wind up computing all the integer bits of the quotient anyway as
21 * a side-effect of computing the remainder by the shift and subtract
22 * method. In practice, this is far more bits than are needed to use
23 * remquo in reduction algorithms.
24 */
25 float
remquof(float x,float y,int * quo)26 remquof(float x, float y, int *quo)
27 {
28 int32_t n,hx,hy,hz,ix,iy,sx,i;
29 u_int32_t q,sxy;
30
31 GET_FLOAT_WORD(hx,x);
32 GET_FLOAT_WORD(hy,y);
33 sxy = (hx ^ hy) & 0x80000000;
34 sx = hx&0x80000000; /* sign of x */
35 hx ^=sx; /* |x| */
36 hy &= 0x7fffffff; /* |y| */
37
38 /* purge off exception values */
39 if(hy==0||hx>=0x7f800000||hy>0x7f800000) /* y=0,NaN;or x not finite */
40 return nan_mix_op(x, y, *)/nan_mix_op(x, y, *);
41 if(hx<hy) {
42 q = 0;
43 goto fixup; /* |x|<|y| return x or x-y */
44 } else if(hx==hy) {
45 *quo = (sxy ? -1 : 1);
46 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
47 }
48
49 /* determine ix = ilogb(x) */
50 if(hx<0x00800000) { /* subnormal x */
51 for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
52 } else ix = (hx>>23)-127;
53
54 /* determine iy = ilogb(y) */
55 if(hy<0x00800000) { /* subnormal y */
56 for (iy = -126,i=(hy<<8); i>0; i<<=1) iy -=1;
57 } else iy = (hy>>23)-127;
58
59 /* set up {hx,lx}, {hy,ly} and align y to x */
60 if(ix >= -126)
61 hx = 0x00800000|(0x007fffff&hx);
62 else { /* subnormal x, shift x to normal */
63 n = -126-ix;
64 hx <<= n;
65 }
66 if(iy >= -126)
67 hy = 0x00800000|(0x007fffff&hy);
68 else { /* subnormal y, shift y to normal */
69 n = -126-iy;
70 hy <<= n;
71 }
72
73 /* fix point fmod */
74 n = ix - iy;
75 q = 0;
76 while(n--) {
77 hz=hx-hy;
78 if(hz<0) hx = hx << 1;
79 else {hx = hz << 1; q++;}
80 q <<= 1;
81 }
82 hz=hx-hy;
83 if(hz>=0) {hx=hz;q++;}
84
85 /* convert back to floating value and restore the sign */
86 if(hx==0) { /* return sign(x)*0 */
87 q &= 0x7fffffff;
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