Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 3ec404d8 authored by Aleksandar Markovic's avatar Aleksandar Markovic Committed by Ralf Baechle
Browse files

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: default avatarMiodrag Dinic <miodrag.dinic@imgtec.com>
Signed-off-by: default avatarGoran Ferenc <goran.ferenc@imgtec.com>
Signed-off-by: default avatarAleksandar 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: default avatarRalf Baechle <ralf@linux-mips.org>
parent 1ff8560a

MAINTAINERS

+7 −0
Original line number Diff line number Diff line
@@ -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

arch/mips/math-emu/Makefile

+4 −2
Original line number Diff line number Diff line
@@ -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 \

arch/mips/math-emu/cp1emu.c

+2 −4
Original line number Diff line number Diff line
@@ -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 @@ static int fpu_emu(struct pt_regs *xcp, struct mips_fpu_struct *ctx, 
				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;

		}

arch/mips/math-emu/dp_rint.c

0 → 100644
+89 −0
Original line number Diff line number Diff line 
/* 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;

}

arch/mips/math-emu/ieee754.h

+2 −0
Original line number Diff line number Diff line
@@ -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);