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Diffstat (limited to 'src/include/utils/pg_crc.h')
| -rw-r--r-- | src/include/utils/pg_crc.h | 107 |
1 files changed, 107 insertions, 0 deletions
diff --git a/src/include/utils/pg_crc.h b/src/include/utils/pg_crc.h new file mode 100644 index 0000000..5fea607 --- /dev/null +++ b/src/include/utils/pg_crc.h @@ -0,0 +1,107 @@ +/* + * 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 */ |