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/arch/mips/math-emu/sp_sqrt.c

https://bitbucket.org/evzijst/gittest
C | 117 lines | 72 code | 11 blank | 34 comment | 14 complexity | 492b0804e50eb8fb243819a087f4144b MD5 | raw file
  1/* IEEE754 floating point arithmetic
  2 * single precision square root
  3 */
  4/*
  5 * MIPS floating point support
  6 * Copyright (C) 1994-2000 Algorithmics Ltd.
  7 * http://www.algor.co.uk
  8 *
  9 * ########################################################################
 10 *
 11 *  This program is free software; you can distribute it and/or modify it
 12 *  under the terms of the GNU General Public License (Version 2) as
 13 *  published by the Free Software Foundation.
 14 *
 15 *  This program is distributed in the hope it will be useful, but WITHOUT
 16 *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 17 *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 18 *  for more details.
 19 *
 20 *  You should have received a copy of the GNU General Public License along
 21 *  with this program; if not, write to the Free Software Foundation, Inc.,
 22 *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
 23 *
 24 * ########################################################################
 25 */
 26
 27
 28#include "ieee754sp.h"
 29
 30ieee754sp ieee754sp_sqrt(ieee754sp x)
 31{
 32	int ix, s, q, m, t, i;
 33	unsigned int r;
 34	COMPXSP;
 35
 36	/* take care of Inf and NaN */
 37
 38	EXPLODEXSP;
 39	CLEARCX;
 40	FLUSHXSP;
 41
 42	/* x == INF or NAN? */
 43	switch (xc) {
 44	case IEEE754_CLASS_QNAN:
 45		/* sqrt(Nan) = Nan */
 46		return ieee754sp_nanxcpt(x, "sqrt");
 47	case IEEE754_CLASS_SNAN:
 48		SETCX(IEEE754_INVALID_OPERATION);
 49		return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
 50	case IEEE754_CLASS_ZERO:
 51		/* sqrt(0) = 0 */
 52		return x;
 53	case IEEE754_CLASS_INF:
 54		if (xs) {
 55			/* sqrt(-Inf) = Nan */
 56			SETCX(IEEE754_INVALID_OPERATION);
 57			return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
 58		}
 59		/* sqrt(+Inf) = Inf */
 60		return x;
 61	case IEEE754_CLASS_DNORM:
 62	case IEEE754_CLASS_NORM:
 63		if (xs) {
 64			/* sqrt(-x) = Nan */
 65			SETCX(IEEE754_INVALID_OPERATION);
 66			return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
 67		}
 68		break;
 69	}
 70
 71	ix = x.bits;
 72
 73	/* normalize x */
 74	m = (ix >> 23);
 75	if (m == 0) {		/* subnormal x */
 76		for (i = 0; (ix & 0x00800000) == 0; i++)
 77			ix <<= 1;
 78		m -= i - 1;
 79	}
 80	m -= 127;		/* unbias exponent */
 81	ix = (ix & 0x007fffff) | 0x00800000;
 82	if (m & 1)		/* odd m, double x to make it even */
 83		ix += ix;
 84	m >>= 1;		/* m = [m/2] */
 85
 86	/* generate sqrt(x) bit by bit */
 87	ix += ix;
 88	q = s = 0;		/* q = sqrt(x) */
 89	r = 0x01000000;		/* r = moving bit from right to left */
 90
 91	while (r != 0) {
 92		t = s + r;
 93		if (t <= ix) {
 94			s = t + r;
 95			ix -= t;
 96			q += r;
 97		}
 98		ix += ix;
 99		r >>= 1;
100	}
101
102	if (ix != 0) {
103		SETCX(IEEE754_INEXACT);
104		switch (ieee754_csr.rm) {
105		case IEEE754_RP:
106			q += 2;
107			break;
108		case IEEE754_RN:
109			q += (q & 1);
110			break;
111		}
112	}
113	ix = (q >> 1) + 0x3f000000;
114	ix += (m << 23);
115	x.bits = ix;
116	return x;
117}