1 /* 2 * pg_crc.h 3 * 4 * PostgreSQL CRC support 5 * 6 * See Ross Williams' excellent introduction 7 * A PAINLESS GUIDE TO CRC ERROR DETECTION ALGORITHMS, available from 8 * http://ross.net/crc/ or several other net sites. 9 * 10 * We have three slightly different variants of a 32-bit CRC calculation: 11 * CRC-32C (Castagnoli polynomial), CRC-32 (Ethernet polynomial), and a legacy 12 * CRC-32 version that uses the lookup table in a funny way. They all consist 13 * of four macros: 14 * 15 * INIT_<variant>(crc) 16 * Initialize a CRC accumulator 17 * 18 * COMP_<variant>(crc, data, len) 19 * Accumulate some (more) bytes into a CRC 20 * 21 * FIN_<variant>(crc) 22 * Finish a CRC calculation 23 * 24 * EQ_<variant>(c1, c2) 25 * Check for equality of two CRCs. 26 * 27 * The CRC-32C variant is in port/pg_crc32c.h. 28 * 29 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group 30 * Portions Copyright (c) 1994, Regents of the University of California 31 * 32 * src/include/utils/pg_crc.h 33 */ 34 #ifndef PG_CRC_H 35 #define PG_CRC_H 36 37 typedef uint32 pg_crc32; 38 39 /* 40 * CRC-32, the same used e.g. in Ethernet. 41 * 42 * This is currently only used in ltree and hstore contrib modules. It uses 43 * the same lookup table as the legacy algorithm below. New code should 44 * use the Castagnoli version instead. 45 */ 46 #define INIT_TRADITIONAL_CRC32(crc) ((crc) = 0xFFFFFFFF) 47 #define FIN_TRADITIONAL_CRC32(crc) ((crc) ^= 0xFFFFFFFF) 48 #define COMP_TRADITIONAL_CRC32(crc, data, len) \ 49 COMP_CRC32_NORMAL_TABLE(crc, data, len, pg_crc32_table) 50 #define EQ_TRADITIONAL_CRC32(c1, c2) ((c1) == (c2)) 51 52 /* Sarwate's algorithm, for use with a "normal" lookup table */ 53 #define COMP_CRC32_NORMAL_TABLE(crc, data, len, table) \ 54 do { \ 55 const unsigned char *__data = (const unsigned char *) (data); \ 56 uint32 __len = (len); \ 57 \ 58 while (__len-- > 0) \ 59 { \ 60 int __tab_index = ((int) (crc) ^ *__data++) & 0xFF; \ 61 (crc) = table[__tab_index] ^ ((crc) >> 8); \ 62 } \ 63 } while (0) 64 65 /* 66 * The CRC algorithm used for WAL et al in pre-9.5 versions. 67 * 68 * This closely resembles the normal CRC-32 algorithm, but is subtly 69 * different. Using Williams' terms, we use the "normal" table, but with 70 * "reflected" code. That's bogus, but it was like that for years before 71 * anyone noticed. It does not correspond to any polynomial in a normal CRC 72 * algorithm, so it's not clear what the error-detection properties of this 73 * algorithm actually are. 74 * 75 * We still need to carry this around because it is used in a few on-disk 76 * structures that need to be pg_upgradeable. It should not be used in new 77 * code. 78 */ 79 #define INIT_LEGACY_CRC32(crc) ((crc) = 0xFFFFFFFF) 80 #define FIN_LEGACY_CRC32(crc) ((crc) ^= 0xFFFFFFFF) 81 #define COMP_LEGACY_CRC32(crc, data, len) \ 82 COMP_CRC32_REFLECTED_TABLE(crc, data, len, pg_crc32_table) 83 #define EQ_LEGACY_CRC32(c1, c2) ((c1) == (c2)) 84 85 /* 86 * Sarwate's algorithm, for use with a "reflected" lookup table (but in the 87 * legacy algorithm, we actually use it on a "normal" table, see above) 88 */ 89 #define COMP_CRC32_REFLECTED_TABLE(crc, data, len, table) \ 90 do { \ 91 const unsigned char *__data = (const unsigned char *) (data); \ 92 uint32 __len = (len); \ 93 \ 94 while (__len-- > 0) \ 95 { \ 96 int __tab_index = ((int) ((crc) >> 24) ^ *__data++) & 0xFF; \ 97 (crc) = table[__tab_index] ^ ((crc) << 8); \ 98 } \ 99 } while (0) 100 101 /* 102 * Constant table for the CRC-32 polynomials. The same table is used by both 103 * the normal and traditional variants. 104 */ 105 extern PGDLLIMPORT const uint32 pg_crc32_table[256]; 106 107 #endif /* PG_CRC_H */ 108