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5028f22f6e
The old algorithm was found to not be the usual CRC-32 algorithm, used by Ethernet et al. We were using a non-reflected lookup table with code meant for a reflected lookup table. That's a strange combination that AFAICS does not correspond to any bit-wise CRC calculation, which makes it difficult to reason about its properties. Although it has worked well in practice, seems safer to use a well-known algorithm. Since we're changing the algorithm anyway, we might as well choose a different polynomial. The Castagnoli polynomial has better error-correcting properties than the traditional CRC-32 polynomial, even if we had implemented it correctly. Another reason for picking that is that some new CPUs have hardware support for calculating CRC-32C, but not CRC-32, let alone our strange variant of it. This patch doesn't add any support for such hardware, but a future patch could now do that. The old algorithm is kept around for tsquery and pg_trgm, which use the values in indexes that need to remain compatible so that pg_upgrade works. While we're at it, share the old lookup table for CRC-32 calculation between hstore, ltree and core. They all use the same table, so might as well.
43 lines
731 B
C
43 lines
731 B
C
/* contrib/ltree/crc32.c */
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/*
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* Implements CRC-32, as used in ltree.
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*
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* Note that the CRC is used in the on-disk format of GiST indexes, so we
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* must stay backwards-compatible!
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*/
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#include "postgres.h"
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#include <sys/types.h>
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#include <stdio.h>
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#include <sys/types.h>
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#ifdef LOWER_NODE
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#include <ctype.h>
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#define TOLOWER(x) tolower((unsigned char) (x))
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#else
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#define TOLOWER(x) (x)
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#endif
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#include "utils/pg_crc.h"
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#include "crc32.h"
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unsigned int
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ltree_crc32_sz(char *buf, int size)
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{
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pg_crc32 crc;
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char *p = buf;
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INIT_TRADITIONAL_CRC32(crc);
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while (size > 0)
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{
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char c = (char) TOLOWER(*p);
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COMP_TRADITIONAL_CRC32(crc, &c, 1);
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size--;
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p++;
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}
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FIN_TRADITIONAL_CRC32(crc);
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return (unsigned int) crc;
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}
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