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MIPS: math-emu: RINT.<D|S>: Fix several problems by reimplementation 

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>
This commit is contained in:
Aleksandar Markovic 2017-08-21 14:24:48 +02:00 committed by Ralf Baechle
parent 1ff8560ac9
commit 3ec404d88c
6 changed files with 194 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
MAINTAINERS
View File

@ -8802,6 +8802,13 @@ F: arch/mips/include/asm/mach-loongson32/
F: drivers/*/*loongson1*
F: drivers/*/*/*loongson1*
MIPS RINT INSTRUCTION EMULATION
M: Aleksandar Markovic <aleksandar.markovic@imgtec.com>
L: linux-mips@linux-mips.org
S: Supported
F: arch/mips/math-emu/sp_rint.c
F: arch/mips/math-emu/dp_rint.c
MIROSOUND PCM20 FM RADIO RECEIVER DRIVER
M: Hans Verkuil <hverkuil@xs4all.nl>
L: linux-media@vger.kernel.org

6
arch/mips/math-emu/Makefile
View File

@ -4,9 +4,11 @@
obj-y += cp1emu.o ieee754dp.o ieee754sp.o ieee754.o \
dp_div.o dp_mul.o dp_sub.o dp_add.o dp_fsp.o dp_cmp.o dp_simple.o \
dp_tint.o dp_fint.o dp_maddf.o dp_2008class.o dp_fmin.o dp_fmax.o \
dp_tint.o dp_fint.o dp_rint.o dp_maddf.o dp_2008class.o dp_fmin.o \
dp_fmax.o \
sp_div.o sp_mul.o sp_sub.o sp_add.o sp_fdp.o sp_cmp.o sp_simple.o \
sp_tint.o sp_fint.o sp_maddf.o sp_2008class.o sp_fmin.o sp_fmax.o \
sp_tint.o sp_fint.o sp_rint.o sp_maddf.o sp_2008class.o sp_fmin.o \
sp_fmax.o \
dsemul.o
lib-y += ieee754d.o \

6
arch/mips/math-emu/cp1emu.c
View File

@ -1805,8 +1805,7 @@ static int fpu_emu(struct pt_regs *xcp, struct mips_fpu_struct *ctx,
return SIGILL;
SPFROMREG(fs, MIPSInst_FS(ir));
rv.l = ieee754sp_tlong(fs);
rv.s = ieee754sp_flong(rv.l);
rv.s = ieee754sp_rint(fs);
goto copcsr;
}
@ -2134,8 +2133,7 @@ copcsr:
return SIGILL;
DPFROMREG(fs, MIPSInst_FS(ir));
rv.l = ieee754dp_tlong(fs);
rv.d = ieee754dp_flong(rv.l);
rv.d = ieee754dp_rint(fs);
goto copcsr;
}

89
arch/mips/math-emu/dp_rint.c Normal file
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@ -0,0 +1,89 @@
/* IEEE754 floating point arithmetic
* double precision: common utilities
*/
/*
* MIPS floating point support
* Copyright (C) 1994-2000 Algorithmics Ltd.
* Copyright (C) 2017 Imagination Technologies, Ltd.
* Author: Aleksandar Markovic <aleksandar.markovic@imgtec.com>
*
* 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.
*/
#include "ieee754dp.h"
union ieee754dp ieee754dp_rint(union ieee754dp x)
{
union ieee754dp ret;
u64 residue;
int sticky;
int round;
int odd;
COMPXDP;
ieee754_clearcx();
EXPLODEXDP;
FLUSHXDP;
if (xc == IEEE754_CLASS_SNAN)
return ieee754dp_nanxcpt(x);
if ((xc == IEEE754_CLASS_QNAN) ||
(xc == IEEE754_CLASS_INF) ||
(xc == IEEE754_CLASS_ZERO))
return x;
if (xe >= DP_FBITS)
return x;
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;
}
odd = (xm & 0x1) != 0x0;
switch (ieee754_csr.rm) {
case FPU_CSR_RN: /* toward nearest */
if (round && (sticky || odd))
xm++;
break;
case FPU_CSR_RZ: /* toward zero */
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;
}
if (round || sticky)
ieee754_setcx(IEEE754_INEXACT);
ret = ieee754dp_flong(xm);
DPSIGN(ret) = xs;
return ret;
}

2
arch/mips/math-emu/ieee754.h
View File

@ -67,6 +67,7 @@ union ieee754sp ieee754sp_div(union ieee754sp x, union ieee754sp y);
union ieee754sp ieee754sp_fint(int x);
union ieee754sp ieee754sp_flong(s64 x);
union ieee754sp ieee754sp_fdp(union ieee754dp x);
union ieee754sp ieee754sp_rint(union ieee754sp x);
int ieee754sp_tint(union ieee754sp x);
s64 ieee754sp_tlong(union ieee754sp x);
@ -101,6 +102,7 @@ union ieee754dp ieee754dp_neg(union ieee754dp x);
union ieee754dp ieee754dp_fint(int x);
union ieee754dp ieee754dp_flong(s64 x);
union ieee754dp ieee754dp_fsp(union ieee754sp x);
union ieee754dp ieee754dp_rint(union ieee754dp x);
int ieee754dp_tint(union ieee754dp x);
s64 ieee754dp_tlong(union ieee754dp x);

90
arch/mips/math-emu/sp_rint.c Normal file
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@ -0,0 +1,90 @@
/* IEEE754 floating point arithmetic
* single precision
*/
/*
* MIPS floating point support
* Copyright (C) 1994-2000 Algorithmics Ltd.
* Copyright (C) 2017 Imagination Technologies, Ltd.
* Author: Aleksandar Markovic <aleksandar.markovic@imgtec.com>
*
* 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.
*/
#include "ieee754sp.h"
union ieee754sp ieee754sp_rint(union ieee754sp x)
{
union ieee754sp ret;
u32 residue;
int sticky;
int round;
int odd;
COMPXDP; /* <-- DP needed for 64-bit mantissa tmp */
ieee754_clearcx();
EXPLODEXSP;
FLUSHXSP;
if (xc == IEEE754_CLASS_SNAN)
return ieee754sp_nanxcpt(x);
if ((xc == IEEE754_CLASS_QNAN) ||
(xc == IEEE754_CLASS_INF) ||
(xc == IEEE754_CLASS_ZERO))
return x;
if (xe >= SP_FBITS)
return x;
if (xe < -1) {
residue = xm;
round = 0;
sticky = residue != 0;
xm = 0;
} else {
residue = xm << (xe + 1);
residue <<= 31 - SP_FBITS;
round = (residue >> 31) != 0;
sticky = (residue << 1) != 0;
xm >>= SP_FBITS - xe;
}
odd = (xm & 0x1) != 0x0;
switch (ieee754_csr.rm) {
case FPU_CSR_RN: /* toward nearest */
if (round && (sticky || odd))
xm++;
break;
case FPU_CSR_RZ: /* toward zero */
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;
}
if (round || sticky)
ieee754_setcx(IEEE754_INEXACT);
ret = ieee754sp_flong(xm);
SPSIGN(ret) = xs;
return ret;
}