linux/arch/mips/math-emu/sp_mul.c

// SPDX-License-Identifier: GPL-2.0-only
/* IEEE754 floating point arithmetic
 * single precision
 */
/*
 * MIPS floating point support
 * Copyright (C) 1994-2000 Algorithmics Ltd.
 */

#include "ieee754sp.h"

union ieee754sp ieee754sp_mul(union ieee754sp x, union ieee754sp y)
{
	int re;
	int rs;
	unsigned int rm;
	unsigned short lxm;
	unsigned short hxm;
	unsigned short lym;
	unsigned short hym;
	unsigned int lrm;
	unsigned int hrm;
	unsigned int t;
	unsigned int at;

	COMPXSP;
	COMPYSP;

	EXPLODEXSP;
	EXPLODEYSP;

	ieee754_clearcx();

	FLUSHXSP;
	FLUSHYSP;

	switch (CLPAIR(xc, yc)) {
	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);

	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
	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);

	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_QNAN):
	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 handling
	 */
	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
		ieee754_setcx(IEEE754_INVALID_OPERATION);
		return ieee754sp_indef();

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

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


	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
		SPDNORMX;
		fallthrough;
	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;
	}
	/* rm = xm * ym, re = xe+ye basically */
	assert(xm & SP_HIDDEN_BIT);
	assert(ym & SP_HIDDEN_BIT);

	re = xe + ye;
	rs = xs ^ ys;

	/* shunt to top of word */
	xm <<= 32 - (SP_FBITS + 1);
	ym <<= 32 - (SP_FBITS + 1);

	/*
	 * Multiply 32 bits xm, ym to give high 32 bits rm with stickness.
	 */
	lxm = xm & 0xffff;
	hxm = xm >> 16;
	lym = ym & 0xffff;
	hym = ym >> 16;

	lrm = lxm * lym;	/* 16 * 16 => 32 */
	hrm = hxm * hym;	/* 16 * 16 => 32 */

	t = lxm * hym; /* 16 * 16 => 32 */
	at = lrm + (t << 16);
	hrm += at < lrm;
	lrm = at;
	hrm = hrm + (t >> 16);

	t = hxm * lym; /* 16 * 16 => 32 */
	at = lrm + (t << 16);
	hrm += at < lrm;
	lrm = at;
	hrm = hrm + (t >> 16);

	rm = hrm | (lrm != 0);

	/*
	 * Sticky shift down to normal rounding precision.
	 */
	if ((int) rm < 0) {
		rm = (rm >> (32 - (SP_FBITS + 1 + 3))) |
		    ((rm << (SP_FBITS + 1 + 3)) != 0);
		re++;
	} else {
		rm = (rm >> (32 - (SP_FBITS + 1 + 3 + 1))) |
		     ((rm << (SP_FBITS + 1 + 3 + 1)) != 0);
	}
	assert(rm & (SP_HIDDEN_BIT << 3));

	return ieee754sp_format(rs, re, rm);
}