sp_sqrt.c
2.36 KB
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/* IEEE754 floating point arithmetic
* single precision square root
*/
/*
* MIPS floating point support
* Copyright (C) 1994-2000 Algorithmics Ltd.
*
* This program is free software; you can distribute it and/or modify it
* under the terms of the GNU General Public License (Version 2) as
* published by the Free Software Foundation.
*
* This program is distributed in the hope it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "ieee754sp.h"
union ieee754sp ieee754sp_sqrt(union ieee754sp x)
{
int ix, s, q, m, t, i;
unsigned int r;
COMPXSP;
/* take care of Inf and NaN */
EXPLODEXSP;
ieee754_clearcx();
FLUSHXSP;
/* x == INF or NAN? */
switch (xc) {
case IEEE754_CLASS_SNAN:
return ieee754sp_nanxcpt(x);
case IEEE754_CLASS_QNAN:
/* sqrt(Nan) = Nan */
return x;
case IEEE754_CLASS_ZERO:
/* sqrt(0) = 0 */
return x;
case IEEE754_CLASS_INF:
if (xs) {
/* sqrt(-Inf) = Nan */
ieee754_setcx(IEEE754_INVALID_OPERATION);
return ieee754sp_indef();
}
/* sqrt(+Inf) = Inf */
return x;
case IEEE754_CLASS_DNORM:
case IEEE754_CLASS_NORM:
if (xs) {
/* sqrt(-x) = Nan */
ieee754_setcx(IEEE754_INVALID_OPERATION);
return ieee754sp_indef();
}
break;
}
ix = x.bits;
/* normalize x */
m = (ix >> 23);
if (m == 0) { /* subnormal x */
for (i = 0; (ix & 0x00800000) == 0; i++)
ix <<= 1;
m -= i - 1;
}
m -= 127; /* unbias exponent */
ix = (ix & 0x007fffff) | 0x00800000;
if (m & 1) /* odd m, double x to make it even */
ix += ix;
m >>= 1; /* m = [m/2] */
/* generate sqrt(x) bit by bit */
ix += ix;
q = s = 0; /* q = sqrt(x) */
r = 0x01000000; /* r = moving bit from right to left */
while (r != 0) {
t = s + r;
if (t <= ix) {
s = t + r;
ix -= t;
q += r;
}
ix += ix;
r >>= 1;
}
if (ix != 0) {
ieee754_setcx(IEEE754_INEXACT);
switch (ieee754_csr.rm) {
case FPU_CSR_RU:
q += 2;
break;
case FPU_CSR_RN:
q += (q & 1);
break;
}
}
ix = (q >> 1) + 0x3f000000;
ix += (m << 23);
x.bits = ix;
return x;
}