linux-kernel - [PATCH v6 04/10] crc32-add-pointer-to-tab.diff

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Message-ID: <4E5EB5EE.806@systemfabricworks.com>
Date:	Wed, 31 Aug 2011 17:30:06 -0500
From:	Bob Pearson <rpearson@...temfabricworks.com>
To:	linux-kernel@...r.kernel.org
CC:	fzago@...temfabricworks.com, rpearson@...temfabricworks.com,
	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>,
	George Spelvin <linux@...izon.com>, akpm@...ux-foundation.org
Subject: [PATCH v6 04/10] crc32-add-pointer-to-tab.diff

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

Signed-off-by: Bob Pearson <rpearson@...temfabricworks.com>

---
 lib/crc32.c |   21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

Index: for-next/lib/crc32.c
===================================================================
--- for-next.orig/lib/crc32.c
+++ for-next/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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