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90d53a91fb
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>
113 lines
2.6 KiB
C
113 lines
2.6 KiB
C
/* IEEE754 floating point arithmetic
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* double precision: common utilities
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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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* 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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* 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#include "ieee754dp.h"
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s64 ieee754dp_tlong(union ieee754dp x)
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{
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u64 residue;
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int round;
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int sticky;
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int odd;
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COMPXDP;
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ieee754_clearcx();
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EXPLODEXDP;
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FLUSHXDP;
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switch (xc) {
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case IEEE754_CLASS_SNAN:
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case IEEE754_CLASS_QNAN:
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ieee754_setcx(IEEE754_INVALID_OPERATION);
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return ieee754di_indef();
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case IEEE754_CLASS_INF:
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ieee754_setcx(IEEE754_INVALID_OPERATION);
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return ieee754di_overflow(xs);
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case IEEE754_CLASS_ZERO:
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return 0;
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case IEEE754_CLASS_DNORM:
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case IEEE754_CLASS_NORM:
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break;
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}
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if (xe >= 63) {
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/* look for valid corner case */
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if (xe == 63 && xs && xm == DP_HIDDEN_BIT)
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return -0x8000000000000000LL;
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/* Set invalid. We will only use overflow for floating
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point overflow */
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ieee754_setcx(IEEE754_INVALID_OPERATION);
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return ieee754di_overflow(xs);
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}
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/* oh gawd */
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if (xe > DP_FBITS) {
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xm <<= xe - DP_FBITS;
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} else if (xe < DP_FBITS) {
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if (xe < -1) {
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residue = xm;
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round = 0;
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sticky = residue != 0;
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xm = 0;
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} else {
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/* Shifting a u64 64 times does not work,
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* so we do it in two steps. Be aware that xe
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* may be -1 */
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residue = xm << (xe + 1);
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residue <<= 63 - DP_FBITS;
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round = (residue >> 63) != 0;
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sticky = (residue << 1) != 0;
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xm >>= DP_FBITS - xe;
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}
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odd = (xm & 0x1) != 0x0;
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switch (ieee754_csr.rm) {
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case FPU_CSR_RN:
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if (round && (sticky || odd))
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xm++;
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break;
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case FPU_CSR_RZ:
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break;
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case FPU_CSR_RU: /* toward +Infinity */
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if ((round || sticky) && !xs)
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xm++;
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break;
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case FPU_CSR_RD: /* toward -Infinity */
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if ((round || sticky) && xs)
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xm++;
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break;
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}
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if ((xm >> 63) != 0) {
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/* This can happen after rounding */
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ieee754_setcx(IEEE754_INVALID_OPERATION);
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return ieee754di_overflow(xs);
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}
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if (round || sticky)
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ieee754_setcx(IEEE754_INEXACT);
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}
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if (xs)
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return -xm;
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else
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return xm;
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}
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