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e_fmodf.c (2704B)
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1 /* e_fmodf.c -- float version of e_fmod.c.
2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3 */
4
5 /*
6 * ====================================================
7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
8 *
9 * Developed at SunPro, a Sun Microsystems, Inc. business.
10 * Permission to use, copy, modify, and distribute this
11 * software is freely granted, provided that this notice
12 * is preserved.
13 * ====================================================
14 */
15
16 #ifndef lint
17 static char rcsid[] = "$FreeBSD: src/lib/msun/src/e_fmodf.c,v 1.6 2002/05/28 17:03:12 alfred Exp $";
18 #endif
19
20 /*
21 * __ieee754_fmodf(x,y)
22 * Return x mod y in exact arithmetic
23 * Method: shift and subtract
24 */
25
26 #include "math.h"
27 #include "math_private.h"
28
29 static const float one = 1.0, Zero[] = {0.0, -0.0,};
30
31 float
32 __ieee754_fmodf(float x, float y)
33 {
34 int32_t n,hx,hy,hz,ix,iy,sx,i;
35
36 GET_FLOAT_WORD(hx,x);
37 GET_FLOAT_WORD(hy,y);
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)|| /* y=0,or x not finite */
44 (hy>0x7f800000)) /* or y is NaN */
45 return (x*y)/(x*y);
46 if(hx<hy) return x; /* |x|<|y| return x */
47 if(hx==hy)
48 return Zero[(u_int32_t)sx>>31]; /* |x|=|y| return x*0*/
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 = 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 = hy<<n;
72 }
73
74 /* fix point fmod */
75 n = ix - iy;
76 while(n--) {
77 hz=hx-hy;
78 if(hz<0){hx = hx+hx;}
79 else {
80 if(hz==0) /* return sign(x)*0 */
81 return Zero[(u_int32_t)sx>>31];
82 hx = hz+hz;
83 }
84 }
85 hz=hx-hy;
86 if(hz>=0) {hx=hz;}
87
88 /* convert back to floating value and restore the sign */
89 if(hx==0) /* return sign(x)*0 */
90 return Zero[(u_int32_t)sx>>31];
91 while(hx<0x00800000) { /* normalize x */
92 hx = hx+hx;
93 iy -= 1;
94 }
95 if(iy>= -126) { /* normalize output */
96 hx = ((hx-0x00800000)|((iy+127)<<23));
97 SET_FLOAT_WORD(x,hx|sx);
98 } else { /* subnormal output */
99 n = -126 - iy;
100 hx >>= n;
101 SET_FLOAT_WORD(x,hx|sx);
102 x *= one; /* create necessary signal */
103 }
104 return x; /* exact output */
105 }