1 /* @(#)e_remainder.c 5.1 93/09/24 */
2 /*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunPro, 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 #if defined(LIBM_SCCS) && !defined(lint)
15 __RCSID("$NetBSD: e_remainder.c,v 1.11 2002/05/26 22:01:52 wiz Exp $");
16 #endif
17
18 /* __ieee754_remainder(x,p)
19 * Return :
20 * returns x REM p = x - [x/p]*p as if in infinite
21 * precise arithmetic, where [x/p] is the (infinite bit)
22 * integer nearest x/p (in half way case choose the even one).
23 * Method :
24 * Based on fmod() return x-[x/p]chopped*p exactlp.
25 */
26
27 #include "math.h"
28 #include "math_private.h"
29
30 static const double zero = 0.0;
31
32
33 double
__ieee754_remainder(double x,double p)34 __ieee754_remainder(double x, double p)
35 {
36 int32_t hx,hp;
37 u_int32_t sx,lx,lp;
38 double p_half;
39
40 EXTRACT_WORDS(hx,lx,x);
41 EXTRACT_WORDS(hp,lp,p);
42 sx = hx&0x80000000;
43 hp &= 0x7fffffff;
44 hx &= 0x7fffffff;
45
46 /* purge off exception values */
47 if((hp|lp)==0) return (x*p)/(x*p); /* p = 0 */
48 if((hx>=0x7ff00000)|| /* x not finite */
49 ((hp>=0x7ff00000)&& /* p is NaN */
50 (((hp-0x7ff00000)|lp)!=0)))
51 return (x*p)/(x*p);
52
53
54 if (hp<=0x7fdfffff) x = __ieee754_fmod(x,p+p); /* now x < 2p */
55 if (((hx-hp)|(lx-lp))==0) return zero*x;
56 x = fabs(x);
57 p = fabs(p);
58 if (hp<0x00200000) {
59 if(x+x>p) {
60 x-=p;
61 if(x+x>=p) x -= p;
62 }
63 } else {
64 p_half = 0.5*p;
65 if(x>p_half) {
66 x-=p;
67 if(x>=p_half) x -= p;
68 }
69 }
70 GET_HIGH_WORD(hx,x);
71 SET_HIGH_WORD(x,hx^sx);
72 return x;
73 }
74