108 lines
3.4 KiB
C
108 lines
3.4 KiB
C
/*
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* pg_crc.h
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*
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* PostgreSQL CRC support
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*
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* See Ross Williams' excellent introduction
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* A PAINLESS GUIDE TO CRC ERROR DETECTION ALGORITHMS, available from
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* http://ross.net/crc/ or several other net sites.
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*
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* We have three slightly different variants of a 32-bit CRC calculation:
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* CRC-32C (Castagnoli polynomial), CRC-32 (Ethernet polynomial), and a legacy
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* CRC-32 version that uses the lookup table in a funny way. They all consist
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* of four macros:
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*
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* INIT_<variant>(crc)
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* Initialize a CRC accumulator
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*
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* COMP_<variant>(crc, data, len)
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* Accumulate some (more) bytes into a CRC
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*
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* FIN_<variant>(crc)
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* Finish a CRC calculation
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*
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* EQ_<variant>(c1, c2)
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* Check for equality of two CRCs.
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*
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* The CRC-32C variant is in port/pg_crc32c.h.
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*
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* Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/utils/pg_crc.h
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*/
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#ifndef PG_CRC_H
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#define PG_CRC_H
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typedef uint32 pg_crc32;
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/*
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* CRC-32, the same used e.g. in Ethernet.
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*
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* This is currently only used in ltree and hstore contrib modules. It uses
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* the same lookup table as the legacy algorithm below. New code should
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* use the Castagnoli version instead.
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*/
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#define INIT_TRADITIONAL_CRC32(crc) ((crc) = 0xFFFFFFFF)
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#define FIN_TRADITIONAL_CRC32(crc) ((crc) ^= 0xFFFFFFFF)
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#define COMP_TRADITIONAL_CRC32(crc, data, len) \
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COMP_CRC32_NORMAL_TABLE(crc, data, len, pg_crc32_table)
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#define EQ_TRADITIONAL_CRC32(c1, c2) ((c1) == (c2))
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/* Sarwate's algorithm, for use with a "normal" lookup table */
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#define COMP_CRC32_NORMAL_TABLE(crc, data, len, table) \
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do { \
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const unsigned char *__data = (const unsigned char *) (data); \
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uint32 __len = (len); \
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\
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while (__len-- > 0) \
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{ \
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int __tab_index = ((int) (crc) ^ *__data++) & 0xFF; \
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(crc) = table[__tab_index] ^ ((crc) >> 8); \
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} \
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} while (0)
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/*
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* The CRC algorithm used for WAL et al in pre-9.5 versions.
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*
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* This closely resembles the normal CRC-32 algorithm, but is subtly
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* different. Using Williams' terms, we use the "normal" table, but with
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* "reflected" code. That's bogus, but it was like that for years before
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* anyone noticed. It does not correspond to any polynomial in a normal CRC
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* algorithm, so it's not clear what the error-detection properties of this
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* algorithm actually are.
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*
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* We still need to carry this around because it is used in a few on-disk
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* structures that need to be pg_upgradeable. It should not be used in new
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* code.
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*/
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#define INIT_LEGACY_CRC32(crc) ((crc) = 0xFFFFFFFF)
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#define FIN_LEGACY_CRC32(crc) ((crc) ^= 0xFFFFFFFF)
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#define COMP_LEGACY_CRC32(crc, data, len) \
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COMP_CRC32_REFLECTED_TABLE(crc, data, len, pg_crc32_table)
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#define EQ_LEGACY_CRC32(c1, c2) ((c1) == (c2))
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/*
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* Sarwate's algorithm, for use with a "reflected" lookup table (but in the
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* legacy algorithm, we actually use it on a "normal" table, see above)
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*/
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#define COMP_CRC32_REFLECTED_TABLE(crc, data, len, table) \
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do { \
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const unsigned char *__data = (const unsigned char *) (data); \
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uint32 __len = (len); \
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\
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while (__len-- > 0) \
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{ \
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int __tab_index = ((int) ((crc) >> 24) ^ *__data++) & 0xFF; \
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(crc) = table[__tab_index] ^ ((crc) << 8); \
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} \
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} while (0)
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/*
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* Constant table for the CRC-32 polynomials. The same table is used by both
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* the normal and traditional variants.
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*/
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extern PGDLLIMPORT const uint32 pg_crc32_table[256];
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#endif /* PG_CRC_H */
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