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Commit 9a1dbf6a authored by Bob Pearson's avatar Bob Pearson Committed by Linus Torvalds
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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: default avatarBob Pearson <rpearson@systemfabricworks.com>
Signed-off-by: default avatarDarrick J. Wong <djwong@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ce4320dd

lib/crc32.c

+14 −3
Original line number Diff line number Diff line
@@ -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);

lib/crc32defs.h

+10 −8
Original line number Diff line number Diff line
@@ -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

lib/gen_crc32table.c

+10 −1
Original line number Diff line number Diff line
@@ -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];