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>

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];