sp_div.c

广州斯道2410普及版II的源代码

/* 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"

ieee754sp ieee754sp_div(ieee754sp x, ieee754sp y)
{
	COMPXSP;
	COMPYSP;

	CLEARCX;

	EXPLODEXSP;
	EXPLODEYSP;

	switch (CLPAIR(xc, yc)) {
	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
		return ieee754sp_nanxcpt(ieee754sp_bestnan(x, y), "div", x,
					 y);

	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
		return ieee754sp_nanxcpt(y, "div", x, y);

	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
		return ieee754sp_nanxcpt(x, "div", x, y);

	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
		return ieee754sp_bestnan(x, y);

	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
		return y;

	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
		return x;


		/* Infinity handeling 
		 */

	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
		SETCX(IEEE754_INVALID_OPERATION);
		return ieee754sp_xcpt(ieee754sp_indef(), "div", x, y);

	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
		return ieee754sp_zero(xs ^ ys);

	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
		return ieee754sp_inf(xs ^ ys);

		/* Zero handeling 
		 */

	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
		SETCX(IEEE754_INVALID_OPERATION);
		return ieee754sp_xcpt(ieee754sp_indef(), "div", x, y);

	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
		SETCX(IEEE754_ZERO_DIVIDE);
		return ieee754sp_xcpt(ieee754sp_inf(xs ^ ys), "div", x, y);

	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
		return ieee754sp_zero(xs == ys ? 0 : 1);

	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
		SPDNORMX;

	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
		SPDNORMY;
		break;

	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
		SPDNORMX;
		break;

	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
		break;
	}
	assert(xm & SP_HIDDEN_BIT);
	assert(ym & SP_HIDDEN_BIT);

	/* provide rounding space */
	xm <<= 3;
	ym <<= 3;

	{
		/* now the dirty work */

		unsigned rm = 0;
		int re = xe - ye;
		unsigned bm;

		for (bm = SP_MBIT(SP_MBITS + 2); bm; bm >>= 1) {
			if (xm >= ym) {
				xm -= ym;
				rm |= bm;
				if (xm == 0)
					break;
			}
			xm <<= 1;
		}
		rm <<= 1;
		if (xm)
			rm |= 1;	/* have remainder, set sticky */

		assert(rm);

		/* normalise rm to rounding precision ?
		 */
		while ((rm >> (SP_MBITS + 3)) == 0) {
			rm <<= 1;
			re--;
		}

		SPNORMRET2(xs == ys ? 0 : 1, re, rm, "div", x, y);
	}
}