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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>
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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17
lib/crc32.c
View File

@ -27,13 +27,13 @@
#include <linux/types.h>
#include "crc32defs.h"
#if CRC_LE_BITS == 8
#if CRC_LE_BITS > 8
# define tole(x) ((__force u32) __constant_cpu_to_le32(x))
#else
# define tole(x) (x)
#endif
#if CRC_BE_BITS == 8
#if CRC_BE_BITS > 8
# define tobe(x) ((__force u32) __constant_cpu_to_be32(x))
#else
# define tobe(x) (x)
@ -45,7 +45,7 @@ MODULE_AUTHOR("Matt Domsch <Matt_Domsch@dell.com>");
MODULE_DESCRIPTION("Ethernet CRC32 calculations");
MODULE_LICENSE("GPL");
#if CRC_LE_BITS == 8 || CRC_BE_BITS == 8
#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)[256])
@ -126,6 +126,12 @@ u32 __pure crc32_le(u32 crc, unsigned char const *p, size_t len)
crc = (crc >> 4) ^ crc32table_le[0][crc & 15];
}
# elif CRC_LE_BITS == 8
/* aka Sarwate algorithm */
while (len--) {
crc ^= *p++;
crc = (crc >> 8) ^ crc32table_le[0][crc & 255];
}
# else
const u32 (*tab)[] = crc32table_le;
crc = (__force u32) __cpu_to_le32(crc);
@ -169,6 +175,11 @@ u32 __pure crc32_be(u32 crc, unsigned char const *p, size_t len)
crc = (crc << 4) ^ crc32table_be[0][crc >> 28];
}
# elif CRC_BE_BITS == 8
while (len--) {
crc ^= *p++ << 24;
crc = (crc << 8) ^ crc32table_be[0][crc >> 24];
}
# else
const u32 (*tab)[] = crc32table_be;
crc = (__force u32) __cpu_to_be32(crc);

18
lib/crc32defs.h
View File

@ -6,27 +6,29 @@
#define CRCPOLY_LE 0xedb88320
#define CRCPOLY_BE 0x04c11db7
/* How many bits at a time to use. Requires a table of 4<<CRC_xx_BITS bytes. */
/* For less performance-sensitive, use 4 */
/* How many bits at a time to use. Valid values are 1, 2, 4, 8, and 32. */
/* For less performance-sensitive, use 4 or 8 */
#ifndef CRC_LE_BITS
# define CRC_LE_BITS 8
# define CRC_LE_BITS 32
#endif
#ifndef CRC_BE_BITS
# define CRC_BE_BITS 8
# define CRC_BE_BITS 32
#endif
/*
* Little-endian CRC computation. Used with serial bit streams sent
* lsbit-first. Be sure to use cpu_to_le32() to append the computed CRC.
*/
#if CRC_LE_BITS > 8 || CRC_LE_BITS < 1 || CRC_LE_BITS & CRC_LE_BITS-1
# error CRC_LE_BITS must be a power of 2 between 1 and 8
#if CRC_LE_BITS > 32 || CRC_LE_BITS < 1 || CRC_LE_BITS == 16 || \
CRC_LE_BITS & CRC_LE_BITS-1
# error "CRC_LE_BITS must be one of {1, 2, 4, 8, 32}"
#endif
/*
* Big-endian CRC computation. Used with serial bit streams sent
* msbit-first. Be sure to use cpu_to_be32() to append the computed CRC.
*/
#if CRC_BE_BITS > 8 || CRC_BE_BITS < 1 || CRC_BE_BITS & CRC_BE_BITS-1
# error CRC_BE_BITS must be a power of 2 between 1 and 8
#if CRC_BE_BITS > 32 || CRC_BE_BITS < 1 || CRC_BE_BITS == 16 || \
CRC_BE_BITS & CRC_BE_BITS-1
# error "CRC_BE_BITS must be one of {1, 2, 4, 8, 32}"
#endif

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];