milsko/external/fdlibm/e_fmod.c

/* @(#)e_fmod.c 1.3 95/01/18 */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunSoft, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

/*
 * __fdlibm_fmod(x,y)
 * Return x mod y in exact arithmetic
 * Method: shift and subtract
 */

#include "math.h"

static const double one = 1.0, Zero[] = {
				   0.0,
				   -0.0,
};

double __fdlibm_fmod(double x, double y) {
	int	 n, hx, hy, hz, ix, iy, sx, i;
	unsigned lx, ly, lz;

	hx = __HI(x);	      /* high word of x */
	lx = __LO(x);	      /* low  word of x */
	hy = __HI(y);	      /* high word of y */
	ly = __LO(y);	      /* low  word of y */
	sx = hx & 0x80000000; /* sign of x */
	hx ^= sx;	      /* |x| */
	hy &= 0x7fffffff;     /* |y| */

	/* purge off exception values */
	if((hy | ly) == 0 || (hx >= 0x7ff00000) ||   /* y=0,or x not finite */
	   ((hy | ((ly | -ly) >> 31)) > 0x7ff00000)) /* or y is NaN */
		return (x * y) / (x * y);
	if(hx <= hy) {
		if((hx < hy) || (lx < ly)) return x; /* |x|<|y| return x */
		if(lx == ly)
			return Zero[(unsigned)sx >> 31]; /* |x|=|y| return x*0*/
	}

	/* determine ix = ilogb(x) */
	if(hx < 0x00100000) { /* subnormal x */
		if(hx == 0) {
			for(ix = -1043, i = lx; i > 0; i <<= 1) ix -= 1;
		} else {
			for(ix = -1022, i = (hx << 11); i > 0; i <<= 1) ix -= 1;
		}
	} else
		ix = (hx >> 20) - 1023;

	/* determine iy = ilogb(y) */
	if(hy < 0x00100000) { /* subnormal y */
		if(hy == 0) {
			for(iy = -1043, i = ly; i > 0; i <<= 1) iy -= 1;
		} else {
			for(iy = -1022, i = (hy << 11); i > 0; i <<= 1) iy -= 1;
		}
	} else
		iy = (hy >> 20) - 1023;

	/* set up {hx,lx}, {hy,ly} and align y to x */
	if(ix >= -1022)
		hx = 0x00100000 | (0x000fffff & hx);
	else { /* subnormal x, shift x to normal */
		n = -1022 - ix;
		if(n <= 31) {
			hx = (hx << n) | (lx >> (32 - n));
			lx <<= n;
		} else {
			hx = lx << (n - 32);
			lx = 0;
		}
	}
	if(iy >= -1022)
		hy = 0x00100000 | (0x000fffff & hy);
	else { /* subnormal y, shift y to normal */
		n = -1022 - iy;
		if(n <= 31) {
			hy = (hy << n) | (ly >> (32 - n));
			ly <<= n;
		} else {
			hy = ly << (n - 32);
			ly = 0;
		}
	}

	/* fix point fmod */
	n = ix - iy;
	while(n--) {
		hz = hx - hy;
		lz = lx - ly;
		if(lx < ly) hz -= 1;
		if(hz < 0) {
			hx = hx + hx + (lx >> 31);
			lx = lx + lx;
		} else {
			if((hz | lz) == 0) /* return sign(x)*0 */
				return Zero[(unsigned)sx >> 31];
			hx = hz + hz + (lz >> 31);
			lx = lz + lz;
		}
	}
	hz = hx - hy;
	lz = lx - ly;
	if(lx < ly) hz -= 1;
	if(hz >= 0) {
		hx = hz;
		lx = lz;
	}

	/* convert back to floating value and restore the sign */
	if((hx | lx) == 0) /* return sign(x)*0 */
		return Zero[(unsigned)sx >> 31];
	while(hx < 0x00100000) { /* normalize x */
		hx = hx + hx + (lx >> 31);
		lx = lx + lx;
		iy -= 1;
	}
	if(iy >= -1022) { /* normalize output */
		hx	= ((hx - 0x00100000) | ((iy + 1023) << 20));
		__HI(x) = hx | sx;
		__LO(x) = lx;
	} else { /* subnormal output */
		n = -1022 - iy;
		if(n <= 20) {
			lx = (lx >> n) | ((unsigned)hx << (32 - n));
			hx >>= n;
		} else if(n <= 31) {
			lx = (hx << (32 - n)) | (lx >> n);
			hx = sx;
		} else {
			lx = hx >> (n - 32);
			hx = sx;
		}
		__HI(x) = hx | sx;
		__LO(x) = lx;
		x *= one; /* create necessary signal */
	}
	return x; /* exact output */
}