linux-kernel - [PATCH 04/14] crc32: Speed up memory table access on powerpc

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Date:	Fri, 06 Jan 2012 21:51:09 -0800
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"Darrick J. Wong" <djwong@...ibm.com>
Cc:	Theodore Tso <tytso@....edu>,
	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>,
	Bob Pearson <rpearson@...temfabricworks.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-crypto <linux-crypto@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Mingming Cao <cmm@...ibm.com>, linux-ext4@...r.kernel.org
Subject: [PATCH 04/14] crc32: Speed up memory table access on powerpc

Replace 2D array references by pointer references in loops.
This change has no effect on X86 code but improves PPC
performance.

From: Bob Pearson <rpearson@...temfabricworks.com>
Signed-off-by: Bob Pearson <rpearson@...temfabricworks.com>
[djwong@...ibm.com: Minor changelog tweaks]
Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
---
 lib/crc32.c |   21 +++++++++++----------
 1 files changed, 11 insertions(+), 10 deletions(-)


diff --git a/lib/crc32.c b/lib/crc32.c
index 7a0e5a9..c93c9ae 100644
--- a/lib/crc32.c
+++ b/lib/crc32.c
@@ -53,20 +53,21 @@ 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)) {

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