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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

Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
Cc: Bob Pearson <rpearson@systemfabricworks.com>
Cc: Frank Zago <fzago@systemfabricworks.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Joakim Tjernlund 2012-01-10 15:10:18 -08:00 committed by Linus Torvalds
parent bfcb2cc798
commit 5742332dea
1 changed files with 11 additions and 10 deletions
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21
lib/crc32.c
View File

@ -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)) {