1
2/* @(#)e_fmod.c 1.3 95/01/18 */
3/*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 */
13
14/*
15 * __ieee754_fmod(x,y)
16 * Return x mod y in exact arithmetic
17 * Method: shift and subtract
18 */
19
20#include "fdlibm.h"
21
22#ifdef __STDC__
23static const double one = 1.0, Zero[] = {0.0, -0.0,};
24#else
25static double one = 1.0, Zero[] = {0.0, -0.0,};
26#endif
27
28#ifdef __STDC__
29	double __ieee754_fmod(double x, double y)
30#else
31	double __ieee754_fmod(x,y)
32	double x,y ;
33#endif
34{
35	int n,hx,hy,hz,ix,iy,sx,i;
36	unsigned lx,ly,lz;
37
38	hx = __HI(x);		/* high word of x */
39	lx = __LO(x);		/* low  word of x */
40	hy = __HI(y);		/* high word of y */
41	ly = __LO(y);		/* low  word of y */
42	sx = hx&0x80000000;		/* sign of x */
43	hx ^=sx;		/* |x| */
44	hy &= 0x7fffffff;	/* |y| */
45
46    /* purge off exception values */
47	if((hy|ly)==0||(hx>=0x7ff00000)||	/* y=0,or x not finite */
48	  ((hy|((ly|-ly)>>31))>0x7ff00000))	/* or y is NaN */
49	    return (x*y)/(x*y);
50	if(hx<=hy) {
51	    if((hx<hy)||(lx<ly)) return x;	/* |x|<|y| return x */
52	    if(lx==ly)
53		return Zero[(unsigned)sx>>31];	/* |x|=|y| return x*0*/
54	}
55
56    /* determine ix = ieee_ilogb(x) */
57	if(hx<0x00100000) {	/* subnormal x */
58	    if(hx==0) {
59		for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
60	    } else {
61		for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
62	    }
63	} else ix = (hx>>20)-1023;
64
65    /* determine iy = ieee_ilogb(y) */
66	if(hy<0x00100000) {	/* subnormal y */
67	    if(hy==0) {
68		for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
69	    } else {
70		for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
71	    }
72	} else iy = (hy>>20)-1023;
73
74    /* set up {hx,lx}, {hy,ly} and align y to x */
75	if(ix >= -1022)
76	    hx = 0x00100000|(0x000fffff&hx);
77	else {		/* subnormal x, shift x to normal */
78	    n = -1022-ix;
79	    if(n<=31) {
80	        hx = (hx<<n)|(lx>>(32-n));
81	        lx <<= n;
82	    } else {
83		hx = lx<<(n-32);
84		lx = 0;
85	    }
86	}
87	if(iy >= -1022)
88	    hy = 0x00100000|(0x000fffff&hy);
89	else {		/* subnormal y, shift y to normal */
90	    n = -1022-iy;
91	    if(n<=31) {
92	        hy = (hy<<n)|(ly>>(32-n));
93	        ly <<= n;
94	    } else {
95		hy = ly<<(n-32);
96		ly = 0;
97	    }
98	}
99
100    /* fix point fmod */
101	n = ix - iy;
102	while(n--) {
103	    hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
104	    if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
105	    else {
106	    	if((hz|lz)==0) 		/* return sign(x)*0 */
107		    return Zero[(unsigned)sx>>31];
108	    	hx = hz+hz+(lz>>31); lx = lz+lz;
109	    }
110	}
111	hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
112	if(hz>=0) {hx=hz;lx=lz;}
113
114    /* convert back to floating value and restore the sign */
115	if((hx|lx)==0) 			/* return sign(x)*0 */
116	    return Zero[(unsigned)sx>>31];
117	while(hx<0x00100000) {		/* normalize x */
118	    hx = hx+hx+(lx>>31); lx = lx+lx;
119	    iy -= 1;
120	}
121	if(iy>= -1022) {	/* normalize output */
122	    hx = ((hx-0x00100000)|((iy+1023)<<20));
123	    __HI(x) = hx|sx;
124	    __LO(x) = lx;
125	} else {		/* subnormal output */
126	    n = -1022 - iy;
127	    if(n<=20) {
128		lx = (lx>>n)|((unsigned)hx<<(32-n));
129		hx >>= n;
130	    } else if (n<=31) {
131		lx = (hx<<(32-n))|(lx>>n); hx = sx;
132	    } else {
133		lx = hx>>(n-32); hx = sx;
134	    }
135	    __HI(x) = hx|sx;
136	    __LO(x) = lx;
137	    x *= one;		/* create necessary signal */
138	}
139	return x;		/* exact output */
140}
141