xref: /freebsd/lib/msun/src/e_remainder.c (revision 74bf4e164ba5851606a27d4feff27717452583e5)
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 #ifndef lint
14 static char rcsid[] = "$FreeBSD$";
15 #endif
16 
17 /* __ieee754_remainder(x,p)
18  * Return :
19  * 	returns  x REM p  =  x - [x/p]*p as if in infinite
20  * 	precise arithmetic, where [x/p] is the (infinite bit)
21  *	integer nearest x/p (in half way case choose the even one).
22  * Method :
23  *	Based on fmod() return x-[x/p]chopped*p exactlp.
24  */
25 
26 #include "math.h"
27 #include "math_private.h"
28 
29 static const double zero = 0.0;
30 
31 
32 double
33 __ieee754_remainder(double x, double p)
34 {
35 	int32_t hx,hp;
36 	u_int32_t sx,lx,lp;
37 	double p_half;
38 
39 	EXTRACT_WORDS(hx,lx,x);
40 	EXTRACT_WORDS(hp,lp,p);
41 	sx = hx&0x80000000;
42 	hp &= 0x7fffffff;
43 	hx &= 0x7fffffff;
44 
45     /* purge off exception values */
46 	if((hp|lp)==0) return (x*p)/(x*p); 	/* p = 0 */
47 	if((hx>=0x7ff00000)||			/* x not finite */
48 	  ((hp>=0x7ff00000)&&			/* p is NaN */
49 	  (((hp-0x7ff00000)|lp)!=0)))
50 	    return (x*p)/(x*p);
51 
52 
53 	if (hp<=0x7fdfffff) x = __ieee754_fmod(x,p+p);	/* now x < 2p */
54 	if (((hx-hp)|(lx-lp))==0) return zero*x;
55 	x  = fabs(x);
56 	p  = fabs(p);
57 	if (hp<0x00200000) {
58 	    if(x+x>p) {
59 		x-=p;
60 		if(x+x>=p) x -= p;
61 	    }
62 	} else {
63 	    p_half = 0.5*p;
64 	    if(x>p_half) {
65 		x-=p;
66 		if(x>=p_half) x -= p;
67 	    }
68 	}
69 	GET_HIGH_WORD(hx,x);
70 	SET_HIGH_WORD(x,hx^sx);
71 	return x;
72 }
73