diff options
| author | Joakim Tjernlund <Joakim.Tjernlund@transmode.se> | 2010-05-24 14:33:31 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-05-25 08:07:06 -0700 |
| commit | 836e2af92503f1642dbc3c3281ec68ec1dd39d2e (patch) | |
| tree | 8b68f906e1ca6f39d159f306623da86f4e02f8cb /lib/crc32.c | |
| parent | d4977c78e9c7dd042f96f4a21d957bc25a561333 (diff) | |
| download | lwn-836e2af92503f1642dbc3c3281ec68ec1dd39d2e.tar.gz lwn-836e2af92503f1642dbc3c3281ec68ec1dd39d2e.zip | |
crc32: major optimization
Precompute more crc32 values(0xcc00, 0xcc0000 and 0xcc000000) into tables.
This increases the table size from 1KB to 4KB but the performance benfit
makes it worth it:
28% faster on MPC8321, 266 MHz
2x faster on Core 2 Duo, 3.1GHz
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib/crc32.c')
| -rw-r--r-- | lib/crc32.c | 24 |
1 files changed, 15 insertions, 9 deletions
diff --git a/lib/crc32.c b/lib/crc32.c index bc5b936e9142..4855995fcde9 100644 --- a/lib/crc32.c +++ b/lib/crc32.c @@ -48,12 +48,20 @@ MODULE_LICENSE("GPL"); #if CRC_LE_BITS == 8 || CRC_BE_BITS == 8 static inline u32 -crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 *tab) +crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 (*tab)[256]) { # ifdef __LITTLE_ENDIAN -# define DO_CRC(x) crc = tab[(crc ^ (x)) & 255 ] ^ (crc >> 8) +# 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] # else -# define DO_CRC(x) crc = tab[((crc >> 24) ^ (x)) & 255] ^ (crc << 8) +# 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] # endif const u32 *b; size_t rem_len; @@ -70,10 +78,7 @@ crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 *tab) b = (const u32 *)buf; for (--b; len; --len) { crc ^= *++b; /* use pre increment for speed */ - DO_CRC(0); - DO_CRC(0); - DO_CRC(0); - DO_CRC(0); + DO_CRC4; } len = rem_len; /* And the last few bytes */ @@ -85,6 +90,7 @@ crc32_body(u32 crc, unsigned char const *buf, size_t len, const u32 *tab) } return crc; #undef DO_CRC +#undef DO_CRC4 } #endif /** @@ -117,7 +123,7 @@ u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len) u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len) { # if CRC_LE_BITS == 8 - const u32 *tab = crc32table_le; + const u32 (*tab)[] = crc32table_le; crc = __cpu_to_le32(crc); crc = crc32_body(crc, p, len, tab); @@ -174,7 +180,7 @@ u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len) u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len) { # if CRC_BE_BITS == 8 - const u32 *tab = crc32table_be; + const u32 (*tab)[] = crc32table_be; crc = __cpu_to_be32(crc); crc = crc32_body(crc, p, len, tab); |