sp_modf.c

来自「自己根据lkd和情境分析」· C语言 代码 · 共 81 行

/* IEEE754 floating point arithmetic
 * single precision
 */
/*
 * MIPS floating point support
 * Copyright (C) 1994-2000 Algorithmics Ltd.  All rights reserved.
 * http://www.algor.co.uk
 *
 * ########################################################################
 *
 *  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 "ieee754sp.h"

/* modf function is always exact for a finite number
*/
ieee754sp ieee754sp_modf(ieee754sp x, ieee754sp * ip)
{
	COMPXSP;

	CLEARCX;

	EXPLODEXSP;

	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 = ieee754sp_zero(xs);
		return x;
	case IEEE754_CLASS_NORM:
		break;
	}
	if (xe < 0) {
		*ip = ieee754sp_zero(xs);
		return x;
	}
	if (xe >= SP_MBITS) {
		*ip = x;
		return ieee754sp_zero(xs);
	}
	/* generate ipart mantissa by clearing bottom bits 
	 */
	*ip = buildsp(xs, xe + SP_EBIAS,
		      ((xm >> (SP_MBITS - xe)) << (SP_MBITS - xe)) &
		      ~SP_HIDDEN_BIT);

	/* generate fpart mantissa by clearing top bits
	 * and normalizing (must be able to normalize)
	 */
	xm = (xm << (32 - (SP_MBITS - xe))) >> (32 - (SP_MBITS - xe));
	if (xm == 0)
		return ieee754sp_zero(xs);

	while ((xm >> SP_MBITS) == 0) {
		xm <<= 1;
		xe--;
	}
	return buildsp(xs, xe + SP_EBIAS, xm & ~SP_HIDDEN_BIT);
}