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Commit 5742332d authored by Joakim Tjernlund's avatar Joakim Tjernlund Committed by Linus Torvalds
Browse files

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: default avatarJoakim 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent bfcb2cc7

lib/crc32.c

+11 −10
Original line number Diff line number Diff line
@@ -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)) {