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/*
* pg_crc.h
*
* PostgreSQL CRC support
*
* See Ross Williams' excellent introduction
* A PAINLESS GUIDE TO CRC ERROR DETECTION ALGORITHMS, available from
* http://ross.net/crc/ or several other net sites.
*
* We have three slightly different variants of a 32-bit CRC calculation:
* CRC-32C (Castagnoli polynomial), CRC-32 (Ethernet polynomial), and a legacy
* CRC-32 version that uses the lookup table in a funny way. They all consist
* of four macros:
*
* INIT_<variant>(crc)
* Initialize a CRC accumulator
*
* COMP_<variant>(crc, data, len)
* Accumulate some (more) bytes into a CRC
*
* FIN_<variant>(crc)
* Finish a CRC calculation
*
* EQ_<variant>(c1, c2)
* Check for equality of two CRCs.
*
* The CRC-32C variant is in port/pg_crc32c.h.
*
* Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/utils/pg_crc.h
*/
#ifndef PG_CRC_H
#define PG_CRC_H
typedef uint32 pg_crc32;
/*
* CRC-32, the same used e.g. in Ethernet.
*
* This is currently only used in ltree and hstore contrib modules. It uses
* the same lookup table as the legacy algorithm below. New code should
* use the Castagnoli version instead.
*/
#define INIT_TRADITIONAL_CRC32(crc) ((crc) = 0xFFFFFFFF)
#define FIN_TRADITIONAL_CRC32(crc) ((crc) ^= 0xFFFFFFFF)
#define COMP_TRADITIONAL_CRC32(crc, data, len) \
COMP_CRC32_NORMAL_TABLE(crc, data, len, pg_crc32_table)
#define EQ_TRADITIONAL_CRC32(c1, c2) ((c1) == (c2))
/* Sarwate's algorithm, for use with a "normal" lookup table */
#define COMP_CRC32_NORMAL_TABLE(crc, data, len, table) \
do { \
const unsigned char *__data = (const unsigned char *) (data); \
uint32 __len = (len); \
\
while (__len-- > 0) \
{ \
int __tab_index = ((int) (crc) ^ *__data++) & 0xFF; \
(crc) = table[__tab_index] ^ ((crc) >> 8); \
} \
} while (0)
/*
* The CRC algorithm used for WAL et al in pre-9.5 versions.
*
* This closely resembles the normal CRC-32 algorithm, but is subtly
* different. Using Williams' terms, we use the "normal" table, but with
* "reflected" code. That's bogus, but it was like that for years before
* anyone noticed. It does not correspond to any polynomial in a normal CRC
* algorithm, so it's not clear what the error-detection properties of this
* algorithm actually are.
*
* We still need to carry this around because it is used in a few on-disk
* structures that need to be pg_upgradeable. It should not be used in new
* code.
*/
#define INIT_LEGACY_CRC32(crc) ((crc) = 0xFFFFFFFF)
#define FIN_LEGACY_CRC32(crc) ((crc) ^= 0xFFFFFFFF)
#define COMP_LEGACY_CRC32(crc, data, len) \
COMP_CRC32_REFLECTED_TABLE(crc, data, len, pg_crc32_table)
#define EQ_LEGACY_CRC32(c1, c2) ((c1) == (c2))
/*
* Sarwate's algorithm, for use with a "reflected" lookup table (but in the
* legacy algorithm, we actually use it on a "normal" table, see above)
*/
#define COMP_CRC32_REFLECTED_TABLE(crc, data, len, table) \
do { \
const unsigned char *__data = (const unsigned char *) (data); \
uint32 __len = (len); \
\
while (__len-- > 0) \
{ \
int __tab_index = ((int) ((crc) >> 24) ^ *__data++) & 0xFF; \
(crc) = table[__tab_index] ^ ((crc) << 8); \
} \
} while (0)
/*
* Constant table for the CRC-32 polynomials. The same table is used by both
* the normal and traditional variants.
*/
extern PGDLLIMPORT const uint32 pg_crc32_table[256];
#endif /* PG_CRC_H */
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