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>
diff --git a/lib/crc32.c b/lib/crc32.c
index bc5b936..4855995 100644
--- a/lib/crc32.c
+++ b/lib/crc32.c
@@ -48,12 +48,20 @@
#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 @@
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 @@
}
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)
{
# 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)
{
# 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);