From 9a1dbf6a29694c9d81b498019f103aee0f8b5b6c Mon Sep 17 00:00:00 2001 From: Bob Pearson Date: Fri, 23 Mar 2012 15:02:23 -0700 Subject: [PATCH] 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/crc32.c | 17 ++++++++++++++--- lib/crc32defs.h | 18 ++++++++++-------- lib/gen_crc32table.c | 11 ++++++++++- 3 files changed, 34 insertions(+), 12 deletions(-) diff --git a/lib/crc32.c b/lib/crc32.c index 7394288c045c..5971f2ad46d5 100644 --- a/lib/crc32.c +++ b/lib/crc32.c @@ -27,13 +27,13 @@ #include #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 "); 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); diff --git a/lib/crc32defs.h b/lib/crc32defs.h index f5a540176571..daa3a5e85f60 100644 --- a/lib/crc32defs.h +++ b/lib/crc32defs.h @@ -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< 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 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]; -- 2.20.1