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

/*
 * IEEE754 floating point arithmetic
 * single precision: MSUB.f (Fused Multiply Subtract)
 * MSUBF.fmt: FPR[fd] = FPR[fd] - (FPR[fs] x FPR[ft])
 *
 * MIPS floating point support
 * Copyright (C) 2015 Imagination Technologies, Ltd.
 * Author: Markos Chandras <markos.chandras@imgtec.com>
 *
 *  This program is free software; you can distribute it and/or modify it
 *  under the terms of the GNU General Public License as published by the
 *  Free Software Foundation; version 2 of the License.
 */

#include "ieee754sp.h"

union ieee754sp ieee754sp_msubf(union ieee754sp z, union ieee754sp x,
				union ieee754sp y)
{
	int re;
	int rs;
	unsigned rm;
	unsigned short lxm;
	unsigned short hxm;
	unsigned short lym;
	unsigned short hym;
	unsigned lrm;
	unsigned hrm;
	unsigned t;
	unsigned at;
	int s;

	COMPXSP;
	COMPYSP;
	u32 zm; int ze; int zs __maybe_unused; int zc;

	EXPLODEXSP;
	EXPLODEYSP;
	EXPLODESP(z, zc, zs, ze, zm)

	FLUSHXSP;
	FLUSHYSP;
	FLUSHSP(z, zc, zs, ze, zm);

	ieee754_clearcx();

	switch (zc) {
	case IEEE754_CLASS_SNAN:
		ieee754_setcx(IEEE754_INVALID_OPERATION);
		return ieee754sp_nanxcpt(z);
	case IEEE754_CLASS_DNORM:
		SPDNORMx(zm, ze);
	/* QNAN is handled separately below */
	}

	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):
		if (zc == IEEE754_CLASS_QNAN)
			return z;
		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):
		if (zc == IEEE754_CLASS_QNAN)
			return z;
		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):
		if (zc == IEEE754_CLASS_INF)
			return ieee754sp_inf(zs);
		/* Multiplication is 0 so just return z */
		return z;

	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
		SPDNORMX;

	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
		if (zc == IEEE754_CLASS_QNAN)
			return z;
		else if (zc == IEEE754_CLASS_INF)
			return ieee754sp_inf(zs);
		SPDNORMY;
		break;

	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
		if (zc == IEEE754_CLASS_QNAN)
			return z;
		else if (zc == IEEE754_CLASS_INF)
			return ieee754sp_inf(zs);
		SPDNORMX;
		break;

	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
		if (zc == IEEE754_CLASS_QNAN)
			return z;
		else if (zc == IEEE754_CLASS_INF)
			return ieee754sp_inf(zs);
		/* fall through to real compuation */
	}

	/* Finally get to do some computation */

	/*
	 * Do the multiplication bit first
	 *
	 * rm = xm * ym, re = xe + ye basically
	 *
	 * At this point xm and ym should have been normalized.
	 */

	/* 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));

	/* And now the subtraction */

	/* Flip sign of r and handle as add */
	rs ^= 1;

	assert(zm & SP_HIDDEN_BIT);

	/*
	 * Provide guard,round and stick bit space.
	 */
	zm <<= 3;

	if (ze > re) {
		/*
		 * Have to shift y fraction right to align.
		 */
		s = ze - re;
		SPXSRSYn(s);
	} else if (re > ze) {
		/*
		 * Have to shift x fraction right to align.
		 */
		s = re - ze;
		SPXSRSYn(s);
	}
	assert(ze == re);
	assert(ze <= SP_EMAX);

	if (zs == rs) {
		/*
		 * Generate 28 bit result of adding two 27 bit numbers
		 * leaving result in zm, zs and ze.
		 */
		zm = zm + rm;

		if (zm >> (SP_FBITS + 1 + 3)) { /* carry out */
			SPXSRSX1(); /* shift preserving sticky */
		}
	} else {
		if (zm >= rm) {
			zm = zm - rm;
		} else {
			zm = rm - zm;
			zs = rs;
		}
		if (zm == 0)
			return ieee754sp_zero(ieee754_csr.rm == FPU_CSR_RD);

		/*
		 * Normalize in extended single precision
		 */
		while ((zm >> (SP_MBITS + 3)) == 0) {
			zm <<= 1;
			ze--;
		}

	}
	return ieee754sp_format(zs, ze, zm);
}