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| author | Bob Pearson <rpearson@systemfabricworks.com> | 2012-03-23 15:02:23 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-03-23 16:58:37 -0700 |
| commit | 9a1dbf6a29694c9d81b498019f103aee0f8b5b6c (patch) | |
| tree | 1f331fa108ea29ccf06a7b5816da4dbcaa12bf2d /lib/gen_crc32table.c | |
| parent | ce4320ddda4c2520fe77194d3c801ad4e8a8aa11 (diff) | |
| download | lwn-9a1dbf6a29694c9d81b498019f103aee0f8b5b6c.tar.gz lwn-9a1dbf6a29694c9d81b498019f103aee0f8b5b6c.zip | |
crc32: make CRC_*_BITS definition correspond to actual bit counts
crc32.c provides a choice of one of several algorithms for computing the
LSB and LSB versions of the CRC32 checksum based on the parameters
CRC_LE_BITS and CRC_BE_BITS.
In the original version the values 1, 2, 4 and 8 respectively selected
versions of the alrogithm that computed the crc 1, 2, 4 and 32 bits as a
time.
This patch series adds a new version that computes the CRC 64 bits at a
time. To make things easier to understand the parameter has been
reinterpreted to actually stand for the number of bits processed in each
step of the algorithm so that the old value 8 has been replaced with the
value 32.
This also allows us to add in a widely used crc algorithm that computes
the crc 8 bits at a time called the Sarwate algorithm.
[djwong@us.ibm.com: Minor changelog tweaks]
Signed-off-by: Bob Pearson <rpearson@systemfabricworks.com>
Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib/gen_crc32table.c')
| -rw-r--r-- | lib/gen_crc32table.c | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/lib/gen_crc32table.c b/lib/gen_crc32table.c index eced7696eb7c..99ac744848fb 100644 --- a/lib/gen_crc32table.c +++ b/lib/gen_crc32table.c @@ -4,8 +4,17 @@ #define ENTRIES_PER_LINE 4 +#if CRC_LE_BITS <= 8 #define LE_TABLE_SIZE (1 << CRC_LE_BITS) +#else +#define LE_TABLE_SIZE 256 +#endif + +#if CRC_BE_BITS <= 8 #define BE_TABLE_SIZE (1 << CRC_BE_BITS) +#else +#define BE_TABLE_SIZE 256 +#endif static uint32_t crc32table_le[4][256]; static uint32_t crc32table_be[4][256]; @@ -24,7 +33,7 @@ static void crc32init_le(void) crc32table_le[0][0] = 0; - for (i = 1 << (CRC_LE_BITS - 1); i; i >>= 1) { + for (i = LE_TABLE_SIZE >> 1; i; i >>= 1) { crc = (crc >> 1) ^ ((crc & 1) ? CRCPOLY_LE : 0); for (j = 0; j < LE_TABLE_SIZE; j += 2 * i) crc32table_le[0][i + j] = crc ^ crc32table_le[0][j]; |