linux/arch/mips/math-emu/dp_tint.c
Maciej W. Rozycki 90d53a91fb MIPS: math-emu: Add IEEE Std 754-2008 NaN encoding emulation
Implement IEEE Std 754-2008 NaN encoding wired to the state of the
FCSR.NAN2008 bit.  Make the interpretation of the quiet bit in NaN data
as follows:

* in the legacy mode originally defined by the MIPS architecture the
  value of 1 denotes an sNaN whereas the value of 0 denotes a qNaN,

* in the 2008 mode introduced with revision 5 of the MIPS architecture
  the value of 0 denotes an sNaN whereas the value of 1 denotes a qNaN,
  following the definition of the preferred NaN encoding introduced with
  IEEE Std 754-2008.

In the 2008 mode, following the requirement of the said standard, quiet
an sNaN where needed by setting the quiet bit to 1 and leaving all the
NaN payload bits unchanged.

Update format conversion operations according to the rules set by IEEE
Std 754-2008 and the MIPS architecture.  Specifically:

* propagate NaN payload bits through conversions between floating-point
  formats such that as much information as possible is preserved and
  specifically a conversion from a narrower format to a wider format and
  then back to the original format does not change a qNaN payload in any
  way,

* conversions from a floating-point to an integer format where the
  source is a NaN, infinity or a value that would convert to an integer
  outside the range of the result format produce, under the default
  exception handling, the respective values defined by the MIPS
  architecture.

In full FPU emulation set the FIR.HAS2008 bit to 1, however do not make
any further FCSR bits writable.

Signed-off-by: Maciej W. Rozycki <macro@imgtec.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Matthew Fortune <Matthew.Fortune@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/11477/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
2016-01-20 00:39:20 +01:00

109 lines
2.5 KiB
C

/* 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"
int ieee754dp_tint(union ieee754dp x)
{
u64 residue;
int round;
int sticky;
int odd;
COMPXDP;
ieee754_clearcx();
EXPLODEXDP;
FLUSHXDP;
switch (xc) {
case IEEE754_CLASS_SNAN:
case IEEE754_CLASS_QNAN:
ieee754_setcx(IEEE754_INVALID_OPERATION);
return ieee754si_indef();
case IEEE754_CLASS_INF:
ieee754_setcx(IEEE754_INVALID_OPERATION);
return ieee754si_overflow(xs);
case IEEE754_CLASS_ZERO:
return 0;
case IEEE754_CLASS_DNORM:
case IEEE754_CLASS_NORM:
break;
}
if (xe > 31) {
/* Set invalid. We will only use overflow for floating
point overflow */
ieee754_setcx(IEEE754_INVALID_OPERATION);
return ieee754si_overflow(xs);
}
/* oh gawd */
if (xe > DP_FBITS) {
xm <<= xe - DP_FBITS;
} else if (xe < DP_FBITS) {
if (xe < -1) {
residue = xm;
round = 0;
sticky = residue != 0;
xm = 0;
} else {
residue = xm << (64 - DP_FBITS + xe);
round = (residue >> 63) != 0;
sticky = (residue << 1) != 0;
xm >>= DP_FBITS - xe;
}
/* Note: At this point upper 32 bits of xm are guaranteed
to be zero */
odd = (xm & 0x1) != 0x0;
switch (ieee754_csr.rm) {
case FPU_CSR_RN:
if (round && (sticky || odd))
xm++;
break;
case FPU_CSR_RZ:
break;
case FPU_CSR_RU: /* toward +Infinity */
if ((round || sticky) && !xs)
xm++;
break;
case FPU_CSR_RD: /* toward -Infinity */
if ((round || sticky) && xs)
xm++;
break;
}
/* look for valid corner case 0x80000000 */
if ((xm >> 31) != 0 && (xs == 0 || xm != 0x80000000)) {
/* This can happen after rounding */
ieee754_setcx(IEEE754_INVALID_OPERATION);
return ieee754si_overflow(xs);
}
if (round || sticky)
ieee754_setcx(IEEE754_INEXACT);
}
if (xs)
return -xm;
else
return xm;
}