xref: /openbmc/linux/arch/mips/math-emu/dp_mul.c (revision c9b02990)

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

#include "ieee754dp.h"

union ieee754dp ieee754dp_mul(union ieee754dp x, union ieee754dp y)
{
	int re;
	int rs;
	u64 rm;
	unsigned int lxm;
	unsigned int hxm;
	unsigned int lym;
	unsigned int hym;
	u64 lrm;
	u64 hrm;
	u64 t;
	u64 at;

	COMPXDP;
	COMPYDP;

	EXPLODEXDP;
	EXPLODEYDP;

	ieee754_clearcx();

	FLUSHXDP;
	FLUSHYDP;

	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 ieee754dp_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 ieee754dp_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 ieee754dp_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 ieee754dp_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 ieee754dp_zero(xs ^ ys);


	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
		DPDNORMX;
		fallthrough;
	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
		DPDNORMY;
		break;

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

	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
		break;
	}
	/* rm = xm * ym, re = xe+ye basically */
	assert(xm & DP_HIDDEN_BIT);
	assert(ym & DP_HIDDEN_BIT);

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

	/* shunt to top of word */
	xm <<= 64 - (DP_FBITS + 1);
	ym <<= 64 - (DP_FBITS + 1);

	/*
	 * Multiply 64 bits xm, ym to give high 64 bits rm with stickness.
	 */

	lxm = xm;
	hxm = xm >> 32;
	lym = ym;
	hym = ym >> 32;

	lrm = DPXMULT(lxm, lym);
	hrm = DPXMULT(hxm, hym);

	t = DPXMULT(lxm, hym);

	at = lrm + (t << 32);
	hrm += at < lrm;
	lrm = at;

	hrm = hrm + (t >> 32);

	t = DPXMULT(hxm, lym);

	at = lrm + (t << 32);
	hrm += at < lrm;
	lrm = at;

	hrm = hrm + (t >> 32);

	rm = hrm | (lrm != 0);

	/*
	 * Sticky shift down to normal rounding precision.
	 */
	if ((s64) rm < 0) {
		rm = (rm >> (64 - (DP_FBITS + 1 + 3))) |
		     ((rm << (DP_FBITS + 1 + 3)) != 0);
		re++;
	} else {
		rm = (rm >> (64 - (DP_FBITS + 1 + 3 + 1))) |
		     ((rm << (DP_FBITS + 1 + 3 + 1)) != 0);
	}
	assert(rm & (DP_HIDDEN_BIT << 3));

	return ieee754dp_format(rs, re, rm);
}