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 /* remainder(x,p)
14 * Return :
15 * returns x REM p = x - [x/p]*p as if in infinite
16 * precise arithmetic, where [x/p] is the (infinite bit)
17 * integer nearest x/p (in half way case choose the even one).
18 * Method :
19 * Based on fmod() return x-[x/p]chopped*p exactlp.
20 */
21
22 #include <float.h>
23 #include <math.h>
24
25 #include "math_private.h"
26
27 static const double zero = 0.0;
28
29
30 double
remainder(double x,double p)31 remainder(double x, double p)
32 {
33 int32_t hx,hp;
34 u_int32_t sx,lx,lp;
35 double p_half;
36
37 EXTRACT_WORDS(hx,lx,x);
38 EXTRACT_WORDS(hp,lp,p);
39 sx = hx&0x80000000;
40 hp &= 0x7fffffff;
41 hx &= 0x7fffffff;
42
43 /* purge off exception values */
44 if((hp|lp)==0) return (x*p)/(x*p); /* p = 0 */
45 if((hx>=0x7ff00000)|| /* x not finite */
46 ((hp>=0x7ff00000)&& /* p is NaN */
47 (((hp-0x7ff00000)|lp)!=0)))
48 return (x*p)/(x*p);
49
50
51 if (hp<=0x7fdfffff) x = fmod(x,p+p); /* now x < 2p */
52 if (((hx-hp)|(lx-lp))==0) return zero*x;
53 x = fabs(x);
54 p = fabs(p);
55 if (hp<0x00200000) {
56 if(x+x>p) {
57 x-=p;
58 if(x+x>=p) x -= p;
59 }
60 } else {
61 p_half = 0.5*p;
62 if(x>p_half) {
63 x-=p;
64 if(x>=p_half) x -= p;
65 }
66 }
67 GET_HIGH_WORD(hx,x);
68 SET_HIGH_WORD(x,hx^sx);
69 return x;
70 }
71 DEF_STD(remainder);
72 LDBL_MAYBE_UNUSED_CLONE(remainder);
73