1/* @(#)e_fmod.c 1.3 95/01/18 */
2/*-
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunSoft, 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#include <sys/cdefs.h>
14__FBSDID("$FreeBSD$");
15
16#include "math.h"
17#include "math_private.h"
18
19static const float Zero[] = {0.0, -0.0,};
20
21/*
22 * Return the IEEE remainder and set *quo to the last n bits of the
23 * quotient, rounded to the nearest integer.  We choose n=31 because
24 * we wind up computing all the integer bits of the quotient anyway as
25 * a side-effect of computing the remainder by the shift and subtract
26 * method.  In practice, this is far more bits than are needed to use
27 * remquo in reduction algorithms.
28 */
29float
30remquof(float x, float y, int *quo)
31{
32	int32_t n,hx,hy,hz,ix,iy,sx,i;
33	u_int32_t q,sxy;
34
35	GET_FLOAT_WORD(hx,x);
36	GET_FLOAT_WORD(hy,y);
37	sxy = (hx ^ hy) & 0x80000000;
38	sx = hx&0x80000000;		/* sign of x */
39	hx ^=sx;		/* |x| */
40	hy &= 0x7fffffff;	/* |y| */
41
42    /* purge off exception values */
43	if(hy==0||hx>=0x7f800000||hy>0x7f800000) /* y=0,NaN;or x not finite */
44	    return (x*y)/(x*y);
45	if(hx<hy) {
46	    q = 0;
47	    goto fixup;	/* |x|<|y| return x or x-y */
48	} else if(hx==hy) {
49	    *quo = (sxy ? -1 : 1);
50	    return Zero[(u_int32_t)sx>>31];	/* |x|=|y| return x*0*/
51	}
52
53    /* determine ix = ilogb(x) */
54	if(hx<0x00800000) {	/* subnormal x */
55	    for (ix = -126,i=(hx<<8); i>0; i<<=1) ix -=1;
56	} else ix = (hx>>23)-127;
57
58    /* determine iy = ilogb(y) */
59	if(hy<0x00800000) {	/* subnormal y */
60	    for (iy = -126,i=(hy<<8); i>0; i<<=1) iy -=1;
61	} else iy = (hy>>23)-127;
62
63    /* set up {hx,lx}, {hy,ly} and align y to x */
64	if(ix >= -126)
65	    hx = 0x00800000|(0x007fffff&hx);
66	else {		/* subnormal x, shift x to normal */
67	    n = -126-ix;
68	    hx <<= n;
69	}
70	if(iy >= -126)
71	    hy = 0x00800000|(0x007fffff&hy);
72	else {		/* subnormal y, shift y to normal */
73	    n = -126-iy;
74	    hy <<= n;
75	}
76
77    /* fix point fmod */
78	n = ix - iy;
79	q = 0;
80	while(n--) {
81	    hz=hx-hy;
82	    if(hz<0) hx = hx << 1;
83	    else {hx = hz << 1; q++;}
84	    q <<= 1;
85	}
86	hz=hx-hy;
87	if(hz>=0) {hx=hz;q++;}
88
89    /* convert back to floating value and restore the sign */
90	if(hx==0) {				/* return sign(x)*0 */
91	    q &= 0x7fffffff;
92	    *quo = (sxy ? -q : q);
93	    return Zero[(u_int32_t)sx>>31];
94	}
95	while(hx<0x00800000) {		/* normalize x */
96	    hx <<= 1;
97	    iy -= 1;
98	}
99	if(iy>= -126) {		/* normalize output */
100	    hx = ((hx-0x00800000)|((iy+127)<<23));
101	} else {		/* subnormal output */
102	    n = -126 - iy;
103	    hx >>= n;
104	}
105fixup:
106	SET_FLOAT_WORD(x,hx);
107	y = fabsf(y);
108	if (y < 0x1p-125f) {
109	    if (x+x>y || (x+x==y && (q & 1))) {
110		q++;
111		x-=y;
112	    }
113	} else if (x>0.5f*y || (x==0.5f*y && (q & 1))) {
114	    q++;
115	    x-=y;
116	}
117	GET_FLOAT_WORD(hx,x);
118	SET_FLOAT_WORD(x,hx^sx);
119	q &= 0x7fffffff;
120	*quo = (sxy ? -q : q);
121	return x;
122}
123