linux-kernel - RE: [patch v3 7/7] crc32: final-cleanup.diff

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Date:	Wed, 10 Aug 2011 17:48:43 +0200
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	"Bob Pearson" <rpearson@...temfabricworks.com>
Cc:	akpm@...ux-foundation.org, fzago@...temfabricworks.com,
	"'George Spelvin'" <linux@...izon.com>,
	linux-kernel@...r.kernel.org
Subject: RE: [patch v3 7/7] crc32: final-cleanup.diff

"Bob Pearson" <rpearson@...temfabricworks.com> wrote on 2011/08/10 17:13:00:

> From: "Bob Pearson" <rpearson@...temfabricworks.com>
> To: "'Joakim Tjernlund'" <joakim.tjernlund@...nsmode.se>
> Cc: <akpm@...ux-foundation.org>, <fzago@...temfabricworks.com>, "'George Spelvin'" <linux@...izon.com>, <linux-kernel@...r.kernel.org>
> Date: 2011/08/10 17:13
> Subject: RE: [patch v3 7/7] crc32: final-cleanup.diff
>
> OK. Can you post your current version of crc32.c? I'll try to merge them
> together.

OK, here it comes again, prefably this should be the first patch
in the series.

>From f5268d74f1a81610820e92785397f1247946ce15 Mon Sep 17 00:00:00 2001
From: Joakim Tjernlund <Joakim.Tjernlund@...nsmode.se>
Date: Fri, 5 Aug 2011 17:49:42 +0200
Subject: [PATCH] crc32: Optimize inner loop.

taking a pointer reference to each row in the crc table matrix,
one can reduce the inner loop with a few insn's on RISC
archs like PowerPC.
---
 lib/crc32.c |   21 +++++++++++----------
 1 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/lib/crc32.c b/lib/crc32.c
index 4855995..b06d1e7 100644
--- a/lib/crc32.c
+++ b/lib/crc32.c
@@ -51,20 +51,21 @@ static inline u32
 crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256])
 {
 # ifdef __LITTLE_ENDIAN
-#  define DO_CRC(x) crc = tab[0][(crc ^ (x)) & 255] ^ (crc >> 8)
-#  define DO_CRC4 crc = tab[3][(crc) & 255] ^ \
-		tab[2][(crc >> 8) & 255] ^ \
-		tab[1][(crc >> 16) & 255] ^ \
-		tab[0][(crc >> 24) & 255]
+#  define DO_CRC(x) crc = t0[(crc ^ (x)) & 255] ^ (crc >> 8)
+#  define DO_CRC4 crc = t3[(crc) & 255] ^ \
+		t2[(crc >> 8) & 255] ^ \
+		t1[(crc >> 16) & 255] ^ \
+		t0[(crc >> 24) & 255]
 # else
-#  define DO_CRC(x) crc = tab[0][((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
-#  define DO_CRC4 crc = tab[0][(crc) & 255] ^ \
-		tab[1][(crc >> 8) & 255] ^ \
-		tab[2][(crc >> 16) & 255] ^ \
-		tab[3][(crc >> 24) & 255]
+#  define DO_CRC(x) crc = t0[((crc >> 24) ^ (x)) & 255] ^ (crc << 8)
+#  define DO_CRC4 crc = t0[(crc) & 255] ^ \
+		t1[(crc >> 8) & 255] ^  \
+		t2[(crc >> 16) & 255] ^	\
+		t3[(crc >> 24) & 255]
 # endif
 	const u32 *b;
 	size_t    rem_len;
+	const u32 *t0=tab[0], *t1=tab[1], *t2=tab[2], *t3=tab[3];

 	/* Align it */
 	if (unlikely((long)buf & 3 && len)) {
--
1.7.3.4

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