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Subject[PATCH 2/6] MIPS: math-emu: RINT.<D|S>: Fix several problems by reimplementation
Date
From: Aleksandar Markovic <aleksandar.markovic@imgtec.com>

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, rescpectively. 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>
---
MAINTAINERS | 7 ++++
arch/mips/math-emu/Makefile | 6 ++-
arch/mips/math-emu/cp1emu.c | 6 +--
arch/mips/math-emu/dp_rint.c | 89 +++++++++++++++++++++++++++++++++++++++++++
arch/mips/math-emu/ieee754.h | 2 +
arch/mips/math-emu/sp_rint.c | 90 ++++++++++++++++++++++++++++++++++++++++++++
6 files changed, 194 insertions(+), 6 deletions(-)
create mode 100644 arch/mips/math-emu/dp_rint.c
create mode 100644 arch/mips/math-emu/sp_rint.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 6f7721d..88bea9e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8803,6 +8803,13 @@ 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
diff --git a/arch/mips/math-emu/Makefile b/arch/mips/math-emu/Makefile
index e9bbc2a..e9f10b8 100644
--- a/arch/mips/math-emu/Makefile
+++ b/arch/mips/math-emu/Makefile
@@ -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 \
diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c
index 520a5ac..cabcf2c 100644
--- a/arch/mips/math-emu/cp1emu.c
+++ b/arch/mips/math-emu/cp1emu.c
@@ -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;
}

diff --git a/arch/mips/math-emu/dp_rint.c b/arch/mips/math-emu/dp_rint.c
new file mode 100644
index 0000000..c3b9077
--- /dev/null
+++ b/arch/mips/math-emu/dp_rint.c
@@ -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;
+}
diff --git a/arch/mips/math-emu/ieee754.h b/arch/mips/math-emu/ieee754.h
index d3be351..92dc8fa 100644
--- a/arch/mips/math-emu/ieee754.h
+++ b/arch/mips/math-emu/ieee754.h
@@ -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);
diff --git a/arch/mips/math-emu/sp_rint.c b/arch/mips/math-emu/sp_rint.c
new file mode 100644
index 0000000..70765b1
--- /dev/null
+++ b/arch/mips/math-emu/sp_rint.c
@@ -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;
+}
--
2.7.4
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