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3ec404d88c
Reimplement RINT.<D|S> kernel emulation so that all RINT.<D|S> specifications are met. For the sake of simplicity, let's analyze RINT.S only. Prior to this patch, RINT.S emulation was essentially implemented as (in pseudocode) <output> = ieee754sp_flong(ieee754sp_tlong(<input>)), where ieee754sp_tlong() and ieee754sp_flong() are functions providing conversion from double to integer, and from integer to double, respectively. On surface, this implementation looks correct, but actually fails in many cases. Following problems were detected: 1. NaN and infinity cases will not be handled properly. The function ieee754sp_flong() never returns NaN nor infinity. 2. For RINT.S, for all inputs larger than LONG_MAX, and smaller than FLT_MAX, the result will be wrong, and the overflow exception will be erroneously set. A similar problem for negative inputs exists as well. 3. For some rounding modes, for some negative inputs close to zero, the return value will be zero, and should be -zero. This is because ieee754sp_flong() never returns -zero. This patch removes the problems above by implementing dedicated functions for RINT.<D|S> emulation. The core of the new function functionality is adapted version of the core of the function ieee754sp_tlong(). However, there are many details that are implemented to match RINT.<D|S> specification. It should be said that the functionality of ieee754sp_tlong() actually closely corresponds to CVT.L.S instruction, and it is used while emulating CVT.L.S. However, RINT.S and CVT.L.S instructions differ in many aspects. This patch fulfills missing support for RINT.<D|S>. Signed-off-by: Miodrag Dinic <miodrag.dinic@imgtec.com> Signed-off-by: Goran Ferenc <goran.ferenc@imgtec.com> Signed-off-by: Aleksandar Markovic <aleksandar.markovic@imgtec.com> Cc: David S. Miller <davem@davemloft.net> Cc: Douglas Leung <douglas.leung@imgtec.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Hans Verkuil <hans.verkuil@cisco.com> Cc: James Hogan <james.hogan@imgtec.com> Cc: Maciej W. Rozycki <macro@imgtec.com> Cc: Masahiro Yamada <yamada.masahiro@socionext.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Cc: Paul Burton <paul.burton@imgtec.com> Cc: Petar Jovanovic <petar.jovanovic@imgtec.com> Cc: Raghu Gandham <raghu.gandham@imgtec.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: linux-mips@linux-mips.org Cc: linux-kernel@vger.kernel.org Patchwork: https://patchwork.linux-mips.org/patch/17141/ Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
91 lines
2.0 KiB
C
91 lines
2.0 KiB
C
/* IEEE754 floating point arithmetic
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* single precision
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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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* Copyright (C) 2017 Imagination Technologies, Ltd.
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* Author: Aleksandar Markovic <aleksandar.markovic@imgtec.com>
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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.
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*/
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#include "ieee754sp.h"
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union ieee754sp ieee754sp_rint(union ieee754sp x)
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{
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union ieee754sp ret;
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u32 residue;
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int sticky;
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int round;
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int odd;
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COMPXDP; /* <-- DP needed for 64-bit mantissa tmp */
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ieee754_clearcx();
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EXPLODEXSP;
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FLUSHXSP;
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if (xc == IEEE754_CLASS_SNAN)
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return ieee754sp_nanxcpt(x);
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if ((xc == IEEE754_CLASS_QNAN) ||
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(xc == IEEE754_CLASS_INF) ||
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(xc == IEEE754_CLASS_ZERO))
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return x;
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if (xe >= SP_FBITS)
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return x;
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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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residue = xm << (xe + 1);
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residue <<= 31 - SP_FBITS;
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round = (residue >> 31) != 0;
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sticky = (residue << 1) != 0;
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xm >>= SP_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: /* toward nearest */
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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: /* toward zero */
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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 (round || sticky)
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ieee754_setcx(IEEE754_INEXACT);
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ret = ieee754sp_flong(xm);
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SPSIGN(ret) = xs;
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return ret;
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}
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