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Subject[PATCH 04/14] crc32: Speed up memory table access on powerpc
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Date
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@systemfabricworks.com>
Signed-off-by: Bob Pearson <rpearson@systemfabricworks.com>
[djwong@us.ibm.com: Minor changelog tweaks]
Signed-off-by: Darrick J. Wong <djwong@us.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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