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torvalds
GitHub Repository: torvalds/linux
 Path: blob/master/arch/mips/math-emu/dp_sub.c
26439 views
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// SPDX-License-Identifier: GPL-2.0-only

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/* IEEE754 floating point arithmetic

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 * double precision: common utilities

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 */

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/*

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 * MIPS floating point support

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 * Copyright (C) 1994-2000 Algorithmics Ltd.

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 */

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#include "ieee754dp.h"

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union ieee754dp ieee754dp_sub(union ieee754dp x, union ieee754dp y)

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{

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	int s;

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	COMPXDP;

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	COMPYDP;

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	EXPLODEXDP;

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	EXPLODEYDP;

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	ieee754_clearcx();

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	FLUSHXDP;

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	FLUSHYDP;

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	switch (CLPAIR(xc, yc)) {

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	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):

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	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):

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	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):

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	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):

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	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):

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		return ieee754dp_nanxcpt(y);

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	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):

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	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):

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	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):

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	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):

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	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):

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	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):

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		return ieee754dp_nanxcpt(x);

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	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):

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	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):

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	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):

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	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):

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		return y;

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	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):

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	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):

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	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):

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	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):

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	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):

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		return x;

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	/*

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	 * Infinity handling

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	 */

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	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):

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		if (xs != ys)

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			return x;

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		ieee754_setcx(IEEE754_INVALID_OPERATION);

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		return ieee754dp_indef();

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	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):

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	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):

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	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):

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		return ieee754dp_inf(ys ^ 1);

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	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):

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	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):

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	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):

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		return x;

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	/*

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	 * Zero handling

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	 */

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	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):

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		if (xs != ys)

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			return x;

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		else

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			return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD);

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	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):

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	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):

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		return x;

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	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):

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	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):

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		/* quick fix up */

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		DPSIGN(y) ^= 1;

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		return y;

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	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):

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		DPDNORMX;

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		fallthrough;

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	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):

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		/* normalize ym,ye */

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		DPDNORMY;

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		break;

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	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):

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		/* normalize xm,xe */

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		DPDNORMX;

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		break;

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	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):

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		break;

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	}

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	/* flip sign of y and handle as add */

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	ys ^= 1;

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	assert(xm & DP_HIDDEN_BIT);

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	assert(ym & DP_HIDDEN_BIT);

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	/* provide guard,round and stick bit dpace */

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	xm <<= 3;

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	ym <<= 3;

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	if (xe > ye) {

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		/*

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		 * Have to shift y fraction right to align

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		 */

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		s = xe - ye;

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		ym = XDPSRS(ym, s);

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		ye += s;

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	} else if (ye > xe) {

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		/*

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		 * Have to shift x fraction right to align

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		 */

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		s = ye - xe;

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		xm = XDPSRS(xm, s);

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		xe += s;

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	}

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	assert(xe == ye);

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	assert(xe <= DP_EMAX);

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	if (xs == ys) {

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		/* generate 28 bit result of adding two 27 bit numbers

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		 */

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		xm = xm + ym;

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		if (xm >> (DP_FBITS + 1 + 3)) { /* carry out */

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			xm = XDPSRS1(xm);	/* shift preserving sticky */

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			xe++;

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		}

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	} else {

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		if (xm >= ym) {

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			xm = xm - ym;

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		} else {

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			xm = ym - xm;

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			xs = ys;

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		}

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		if (xm == 0) {

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			if (ieee754_csr.rm == FPU_CSR_RD)

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				return ieee754dp_zero(1);	/* round negative inf. => sign = -1 */

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			else

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				return ieee754dp_zero(0);	/* other round modes   => sign = 1 */

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		}

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		/* normalize to rounding precision

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		 */

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		while ((xm >> (DP_FBITS + 3)) == 0) {

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			xm <<= 1;

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			xe--;

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		}

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	}

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	return ieee754dp_format(xs, xe, xm);

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}

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