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crc32: make CRC_*_BITS definition correspond to actual bit counts

Browse source 
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>
This commit is contained in:
Bob Pearson 2012-03-23 15:02:23 -07:00 • committed by Linus Torvalds
parent ce4320ddda
commit 9a1dbf6a29
3 changed files with 34 additions and 12 deletions
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11
lib/gen_crc32table.c
View file

@ -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];