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awilliam
GitHub Repository: awilliam/linux-vfio
 Path: blob/master/arch/mips/math-emu/sp_sqrt.c
10820 views
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/* IEEE754 floating point arithmetic

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 * single precision square root

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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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 * ########################################################################

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 *

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 *  This program is free software; you can distribute it and/or modify it

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 *  under the terms of the GNU General Public License (Version 2) as

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 *  published by the Free Software Foundation.

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 *

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 *  This program is distributed in the hope it will be useful, but WITHOUT

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 *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

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 *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

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 *  for more details.

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 *

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 *  You should have received a copy of the GNU General Public License along

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 *  with this program; if not, write to the Free Software Foundation, Inc.,

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 *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.

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 *

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 * ########################################################################

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 */

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#include "ieee754sp.h"

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ieee754sp ieee754sp_sqrt(ieee754sp x)

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{

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	int ix, s, q, m, t, i;

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	unsigned int r;

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	COMPXSP;

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	/* take care of Inf and NaN */

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	EXPLODEXSP;

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	CLEARCX;

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	FLUSHXSP;

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	/* x == INF or NAN? */

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	switch (xc) {

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	case IEEE754_CLASS_QNAN:

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		/* sqrt(Nan) = Nan */

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		return ieee754sp_nanxcpt(x, "sqrt");

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	case IEEE754_CLASS_SNAN:

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		SETCX(IEEE754_INVALID_OPERATION);

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		return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");

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	case IEEE754_CLASS_ZERO:

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		/* sqrt(0) = 0 */

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		return x;

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	case IEEE754_CLASS_INF:

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		if (xs) {

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			/* sqrt(-Inf) = Nan */

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			SETCX(IEEE754_INVALID_OPERATION);

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			return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");

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		}

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		/* sqrt(+Inf) = Inf */

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		return x;

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	case IEEE754_CLASS_DNORM:

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	case IEEE754_CLASS_NORM:

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		if (xs) {

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			/* sqrt(-x) = Nan */

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			SETCX(IEEE754_INVALID_OPERATION);

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			return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");

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		}

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		break;

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	}

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	ix = x.bits;

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	/* normalize x */

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	m = (ix >> 23);

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	if (m == 0) {		/* subnormal x */

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		for (i = 0; (ix & 0x00800000) == 0; i++)

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			ix <<= 1;

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		m -= i - 1;

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	}

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	m -= 127;		/* unbias exponent */

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	ix = (ix & 0x007fffff) | 0x00800000;

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	if (m & 1)		/* odd m, double x to make it even */

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		ix += ix;

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	m >>= 1;		/* m = [m/2] */

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	/* generate sqrt(x) bit by bit */

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	ix += ix;

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	q = s = 0;		/* q = sqrt(x) */

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	r = 0x01000000;		/* r = moving bit from right to left */

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	while (r != 0) {

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		t = s + r;

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		if (t <= ix) {

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			s = t + r;

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			ix -= t;

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			q += r;

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		}

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		ix += ix;

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		r >>= 1;

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	}

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	if (ix != 0) {

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		SETCX(IEEE754_INEXACT);

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		switch (ieee754_csr.rm) {

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		case IEEE754_RP:

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			q += 2;

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			break;

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		case IEEE754_RN:

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			q += (q & 1);

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			break;

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		}

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	}

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	ix = (q >> 1) + 0x3f000000;

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	ix += (m << 23);

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	x.bits = ix;

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	return x;

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}

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