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://www.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) 1996-2019, 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
37typedef 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) \
54do { \
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) \
90do { \
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 */
105extern PGDLLIMPORT const uint32 pg_crc32_table[256];
106
107#endif /* PG_CRC_H */
108