Atlas - e_fmod.c
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1/*
2 * ====================================================
3 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
4 *
5 * Developed at SunPro, a Sun Microsystems, Inc. business.
6 * Permission to use, copy, modify, and distribute this
7 * software is freely granted, provided that this notice
8 * is preserved.
9 * ====================================================
10 */
11
12/*
13 * __ieee754_fmod(x,y)
14 * Return x mod y in exact arithmetic
15 * Method: shift and subtract
16 */
17
18#include "math_libm.h"
19#include "math_private.h"
20
21static const double one = 1.0, Zero[] = {0.0, -0.0,};
22
23double attribute_hidden __ieee754_fmod(double x, double y)
24{
25	int32_t n,hx,hy,hz,ix,iy,sx,i;
26	u_int32_t lx,ly,lz;
27
28	EXTRACT_WORDS(hx,lx,x);
29	EXTRACT_WORDS(hy,ly,y);
30	sx = hx&0x80000000;		/* sign of x */
31	hx ^=sx;		/* |x| */
32	hy &= 0x7fffffff;	/* |y| */
33
34    /* purge off exception values */
35	if((hy|ly)==0||(hx>=0x7ff00000)||	/* y=0,or x not finite */
36	  ((hy|((ly|-(int32_t)ly)>>31))>0x7ff00000))	/* or y is NaN */
37	    return (x*y)/(x*y);
38	if(hx<=hy) {
39	    if((hx<hy)||(lx<ly)) return x;	/* |x|<|y| return x */
40	    if(lx==ly)
41		return Zero[(u_int32_t)sx>>31];	/* |x|=|y| return x*0*/
42	}
43
44    /* determine ix = ilogb(x) */
45	if(hx<0x00100000) {	/* subnormal x */
46	    if(hx==0) {
47		for (ix = -1043, i=lx; i>0; i<<=1) ix -=1;
48	    } else {
49		for (ix = -1022,i=(hx<<11); i>0; i<<=1) ix -=1;
50	    }
51	} else ix = (hx>>20)-1023;
52
53    /* determine iy = ilogb(y) */
54	if(hy<0x00100000) {	/* subnormal y */
55	    if(hy==0) {
56		for (iy = -1043, i=ly; i>0; i<<=1) iy -=1;
57	    } else {
58		for (iy = -1022,i=(hy<<11); i>0; i<<=1) iy -=1;
59	    }
60	} else iy = (hy>>20)-1023;
61
62    /* set up {hx,lx}, {hy,ly} and align y to x */
63	if(ix >= -1022)
64	    hx = 0x00100000|(0x000fffff&hx);
65	else {		/* subnormal x, shift x to normal */
66	    n = -1022-ix;
67	    if(n<=31) {
68	        hx = (hx<<n)|(lx>>(32-n));
69	        lx <<= n;
70	    } else {
71		hx = lx<<(n-32);
72		lx = 0;
73	    }
74	}
75	if(iy >= -1022)
76	    hy = 0x00100000|(0x000fffff&hy);
77	else {		/* subnormal y, shift y to normal */
78	    n = -1022-iy;
79	    if(n<=31) {
80	        hy = (hy<<n)|(ly>>(32-n));
81	        ly <<= n;
82	    } else {
83		hy = ly<<(n-32);
84		ly = 0;
85	    }
86	}
87
88    /* fix point fmod */
89	n = ix - iy;
90	while(n--) {
91	    hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
92	    if(hz<0){hx = hx+hx+(lx>>31); lx = lx+lx;}
93	    else {
94	    	if((hz|lz)==0) 		/* return sign(x)*0 */
95		    return Zero[(u_int32_t)sx>>31];
96	    	hx = hz+hz+(lz>>31); lx = lz+lz;
97	    }
98	}
99	hz=hx-hy;lz=lx-ly; if(lx<ly) hz -= 1;
100	if(hz>=0) {hx=hz;lx=lz;}
101
102    /* convert back to floating value and restore the sign */
103	if((hx|lx)==0) 			/* return sign(x)*0 */
104	    return Zero[(u_int32_t)sx>>31];
105	while(hx<0x00100000) {		/* normalize x */
106	    hx = hx+hx+(lx>>31); lx = lx+lx;
107	    iy -= 1;
108	}
109	if(iy>= -1022) {	/* normalize output */
110	    hx = ((hx-0x00100000)|((iy+1023)<<20));
111	    INSERT_WORDS(x,hx|sx,lx);
112	} else {		/* subnormal output */
113	    n = -1022 - iy;
114	    if(n<=20) {
115		lx = (lx>>n)|((u_int32_t)hx<<(32-n));
116		hx >>= n;
117	    } else if (n<=31) {
118		lx = (hx<<(32-n))|(lx>>n); hx = sx;
119	    } else {
120		lx = hx>>(n-32); hx = sx;
121	    }
122	    INSERT_WORDS(x,hx|sx,lx);
123	    x *= one;		/* create necessary signal */
124	}
125	return x;		/* exact output */
126}
127
128/*
129 * wrapper fmod(x,y)
130 */
131#ifndef _IEEE_LIBM
132double fmod(double x, double y)
133{
134	double z = __ieee754_fmod(x, y);
135	if (_LIB_VERSION == _IEEE_ || isnan(y) || isnan(x))
136		return z;
137	if (y == 0.0)
138		return __kernel_standard(x, y, 27); /* fmod(x,0) */
139	return z;
140}
141#else
142strong_alias(__ieee754_fmod, fmod)
143#endif
144libm_hidden_def(fmod)
145
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