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 hx, hy, hz, ix, iy, n, sx;
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)
51 ix = subnormal_ilogbf(hx);
52 else
53 ix = (hx>>23)-127;
54
55 /* determine iy = ilogb(y) */
56 if(hy<0x00800000)
57 iy = subnormal_ilogbf(hy);
58 else
59 iy = (hy>>23)-127;
60
61 /* set up {hx,lx}, {hy,ly} and align y to x */
62 if(ix >= -126)
63 hx = 0x00800000|(0x007fffff&hx);
64 else { /* subnormal x, shift x to normal */
65 n = -126-ix;
66 hx <<= n;
67 }
68 if(iy >= -126)
69 hy = 0x00800000|(0x007fffff&hy);
70 else { /* subnormal y, shift y to normal */
71 n = -126-iy;
72 hy <<= n;
73 }
74
75 /* fix point fmod */
76 n = ix - iy;
77 q = 0;
78 while(n--) {
79 hz=hx-hy;
80 if(hz<0) hx = hx << 1;
81 else {hx = hz << 1; q++;}
82 q <<= 1;
83 }
84 hz=hx-hy;
85 if(hz>=0) {hx=hz;q++;}
86
87 /* convert back to floating value and restore the sign */
88 if(hx==0) { /* return sign(x)*0 */
89 q &= 0x7fffffff;
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