dp_modf.c

/* IEEE754 floating point arithmetic
 * double precision: common utilities
 */
/*
 * MIPS floating point support
 * Copyright (C) 1994-2000 Algorithmics Ltd.
 *
 * ########################################################################
 *
 *  This program is free software; you can distribute it and/or modify it
 *  under the terms of the GNU General Public License (Version 2) as
 *  published by the Free Software Foundation.
 *
 *  This program is distributed in the hope it will be useful, but WITHOUT
 *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 *  for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
 *
 * ########################################################################
 */


#include "ieee754dp.h"

/* modf function is always exact for a finite number
*/
ieee754dp ieee754dp_modf(ieee754dp x, ieee754dp *ip)
{
	COMPXDP;

	CLEARCX;

	EXPLODEXDP;

	switch (xc) {
	case IEEE754_CLASS_SNAN:
	case IEEE754_CLASS_QNAN:
	case IEEE754_CLASS_INF:
	case IEEE754_CLASS_ZERO:
		*ip = x;
		return x;
	case IEEE754_CLASS_DNORM:
		/* far to small */
		*ip = ieee754dp_zero(xs);
		return x;
	case IEEE754_CLASS_NORM:
		break;
	}
	if (xe < 0) {
		*ip = ieee754dp_zero(xs);
		return x;
	}
	if (xe >= DP_MBITS) {
		*ip = x;
		return ieee754dp_zero(xs);
	}
	/* generate ipart mantissa by clearing bottom bits
	 */
	*ip = builddp(xs, xe + DP_EBIAS,
		      ((xm >> (DP_MBITS - xe)) << (DP_MBITS - xe)) &
		      ~DP_HIDDEN_BIT);

	/* generate fpart mantissa by clearing top bits
	 * and normalizing (must be able to normalize)
	 */
	xm = (xm << (64 - (DP_MBITS - xe))) >> (64 - (DP_MBITS - xe));
	if (xm == 0)
		return ieee754dp_zero(xs);

	while ((xm >> DP_MBITS) == 0) {
		xm <<= 1;
		xe--;
	}
	return builddp(xs, xe + DP_EBIAS, xm & ~DP_HIDDEN_BIT);
}