From 9a1dbf6a29694c9d81b498019f103aee0f8b5b6c Mon Sep 17 00:00:00 2001 From: Bob Pearson Date: Fri, 23 Mar 2012 15:02:23 -0700 Subject: 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 Signed-off-by: Darrick J. Wong Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- lib/gen_crc32table.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'lib/gen_crc32table.c') diff --git a/lib/gen_crc32table.c b/lib/gen_crc32table.c index eced7696eb7..99ac744848f 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]; -- cgit v1.2.3