1/* @(#)e_fmod.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#if defined(LIBM_SCCS) && !defined(lint)
14static char rcsid[] = "$NetBSD: e_fmod.c,v 1.8 1995/05/10 20:45:07 jtc Exp $";
15#endif
16
17/*
18 * __ieee754_fmod(x,y)
19 * Return x mod y in exact arithmetic
20 * Method: shift and subtract
21 */
22
23#include "math.h"
24#include "math_private.h"
25
26#ifdef __STDC__
27static const double one = 1.0, Zero[] = {0.0, -0.0,};
28#else
29static double one = 1.0, Zero[] = {0.0, -0.0,};
30#endif
31
32#ifdef __STDC__
33	double __ieee754_fmod(double x, double y)
34#else
35	double __ieee754_fmod(x,y)
36	double x,y ;
37#endif
38{
39	int32_t n,hx,hy,hz,ix,iy,sx,i;
40	u_int32_t lx,ly,lz;
41
42	EXTRACT_WORDS(hx,lx,x);
43	EXTRACT_WORDS(hy,ly,y);
44	sx = hx&0x80000000;		/* sign of x */
45	hx ^=sx;		/* |x| */
46	hy &= 0x7fffffff;	/* |y| */
47
48    /* purge off exception values */
49	if((hy|ly)==0||(hx>=0x7ff00000)||	/* y=0,or x not finite */
50	  ((hy|((ly|-ly)>>31))>0x7ff00000))	/* or y is NaN */
51	    return (x*y)/(x*y);
52	if(hx<=hy) {
53	    if((hx<hy)||(lx<ly)) return x;	/* |x|<|y| return x */
54	    if(lx==ly)
55		return Zero[(u_int32_t)sx>>31];	/* |x|=|y| return x*0*/
56	}
57
58    /* determine ix = ilogb(x) */
59	if(hx<0x00100000) {	/* subnormal x */
60	    if(hx==0) {
61		for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
62	    } else {
63		for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
64	    }
65	} else ix = (hx>>20)-1023;
66
67    /* determine iy = ilogb(y) */
68	if(hy<0x00100000) {	/* subnormal y */
69	    if(hy==0) {
70		for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
71	    } else {
72		for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
73	    }
74	} else iy = (hy>>20)-1023;
75
76    /* set up {hx,lx}, {hy,ly} and align y to x */
77	if(ix >= -1022)
78	    hx = 0x00100000|(0x000fffff&hx);
79	else {		/* subnormal x, shift x to normal */
80	    n = -1022-ix;
81	    if(n<=31) {
82	        hx = (hx<<n)|(lx>>(32-n));
83	        lx <<= n;
84	    } else {
85		hx = lx<<(n-32);
86		lx = 0;
87	    }
88	}
89	if(iy >= -1022)
90	    hy = 0x00100000|(0x000fffff&hy);
91	else {		/* subnormal y, shift y to normal */
92	    n = -1022-iy;
93	    if(n<=31) {
94	        hy = (hy<<n)|(ly>>(32-n));
95	        ly <<= n;
96	    } else {
97		hy = ly<<(n-32);
98		ly = 0;
99	    }
100	}
101
102    /* fix point fmod */
103	n = ix - iy;
104	while(n--) {
105	    hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
106	    if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
107	    else {
108	    	if((hz|lz)==0) 		/* return sign(x)*0 */
109		    return Zero[(u_int32_t)sx>>31];
110	    	hx = hz+hz+(lz>>31); lx = lz+lz;
111	    }
112	}
113	hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
114	if(hz>=0) {hx=hz;lx=lz;}
115
116    /* convert back to floating value and restore the sign */
117	if((hx|lx)==0) 			/* return sign(x)*0 */
118	    return Zero[(u_int32_t)sx>>31];
119	while(hx<0x00100000) {		/* normalize x */
120	    hx = hx+hx+(lx>>31); lx = lx+lx;
121	    iy -= 1;
122	}
123	if(iy>= -1022) {	/* normalize output */
124	    hx = ((hx-0x00100000)|((iy+1023)<<20));
125	    INSERT_WORDS(x,hx|sx,lx);
126	} else {		/* subnormal output */
127	    n = -1022 - iy;
128	    if(n<=20) {
129		lx = (lx>>n)|((u_int32_t)hx<<(32-n));
130		hx >>= n;
131	    } else if (n<=31) {
132		lx = (hx<<(32-n))|(lx>>n); hx = sx;
133	    } else {
134		lx = hx>>(n-32); hx = sx;
135	    }
136	    INSERT_WORDS(x,hx|sx,lx);
137	    x *= one;		/* create necessary signal */
138	}
139	return x;		/* exact output */
140}
141