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/* IEEE754 floating point arithmetic
* double precision: common utilities
*/
/*
* 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 "ieee754dp.h"
union ieee754dp ieee754dp_sub(union ieee754dp x, union ieee754dp y)
{
int s;
COMPXDP;
COMPYDP;
EXPLODEXDP;
EXPLODEYDP;
ieee754_clearcx();
FLUSHXDP;
FLUSHYDP;
switch (CLPAIR(xc, yc)) {
case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
case CLPAIR(IEEE754_CLASS_SNAN, 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):
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):
ieee754_setcx(IEEE754_INVALID_OPERATION);
return ieee754dp_nanxcpt(ieee754dp_indef());
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_INF):
if (xs != ys)
return x;
ieee754_setcx(IEEE754_INVALID_OPERATION);
return ieee754dp_indef();
case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
return ieee754dp_inf(ys ^ 1);
case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
return x;
/*
* Zero handling
*/
case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
if (xs != ys)
return x;
else
return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD);
case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
return x;
case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
/* quick fix up */
DPSIGN(y) ^= 1;
return y;
case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
DPDNORMX;
/* FALL THROUGH */
case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
/* normalize ym,ye */
DPDNORMY;
break;
case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
/* normalize xm,xe */
DPDNORMX;
break;
case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
break;
}
/* flip sign of y and handle as add */
ys ^= 1;
assert(xm & DP_HIDDEN_BIT);
assert(ym & DP_HIDDEN_BIT);
/* provide guard,round and stick bit dpace */
xm <<= 3;
ym <<= 3;
if (xe > ye) {
/*
* Have to shift y fraction right to align
*/
s = xe - ye;
ym = XDPSRS(ym, s);
ye += s;
} else if (ye > xe) {
/*
* Have to shift x fraction right to align
*/
s = ye - xe;
xm = XDPSRS(xm, s);
xe += s;
}
assert(xe == ye);
assert(xe <= DP_EMAX);
if (xs == ys) {
/* generate 28 bit result of adding two 27 bit numbers
*/
xm = xm + ym;
if (xm >> (DP_FBITS + 1 + 3)) { /* carry out */
xm = XDPSRS1(xm); /* shift preserving sticky */
xe++;
}
} else {
if (xm >= ym) {
xm = xm - ym;
} else {
xm = ym - xm;
xs = ys;
}
if (xm == 0) {
if (ieee754_csr.rm == FPU_CSR_RD)
return ieee754dp_zero(1); /* round negative inf. => sign = -1 */
else
return ieee754dp_zero(0); /* other round modes => sign = 1 */
}
/* normalize to rounding precision
*/
while ((xm >> (DP_FBITS + 3)) == 0) {
xm <<= 1;
xe--;
}
}
return ieee754dp_format(xs, xe, xm);
}
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