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/*-------------------------------------------------------------------------
*
* hashfn.c
* Hash functions for use in dynahash.c hashtables
*
*
* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/hash/hashfn.c,v 1.32 2008/01/01 19:45:53 momjian Exp $
*
* NOTES
* It is expected that every bit of a hash function's 32-bit result is
* as random as every other; failure to ensure this is likely to lead
* to poor performance of hash tables. In most cases a hash
* function should use hash_any() or its variant hash_uint32().
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/hash.h"
#include "nodes/bitmapset.h"
/*
* string_hash: hash function for keys that are null-terminated strings.
*
* NOTE: this is the default hash function if none is specified.
*/
uint32
string_hash(const void *key, Size keysize)
{
/*
* If the string exceeds keysize-1 bytes, we want to hash only that many,
* because when it is copied into the hash table it will be truncated at
* that length.
*/
Size s_len = strlen((const char *) key);
s_len = Min(s_len, keysize - 1);
return DatumGetUInt32(hash_any((const unsigned char *) key,
(int) s_len));
}
/*
* tag_hash: hash function for fixed-size tag values
*/
uint32
tag_hash(const void *key, Size keysize)
{
return DatumGetUInt32(hash_any((const unsigned char *) key,
(int) keysize));
}
/*
* oid_hash: hash function for keys that are OIDs
*
* (tag_hash works for this case too, but is slower)
*/
uint32
oid_hash(const void *key, Size keysize)
{
Assert(keysize == sizeof(Oid));
return DatumGetUInt32(hash_uint32((uint32) *((const Oid *) key)));
}
/*
* bitmap_hash: hash function for keys that are (pointers to) Bitmapsets
*
* Note: don't forget to specify bitmap_match as the match function!
*/
uint32
bitmap_hash(const void *key, Size keysize)
{
Assert(keysize == sizeof(Bitmapset *));
return bms_hash_value(*((const Bitmapset *const *) key));
}
/*
* bitmap_match: match function to use with bitmap_hash
*/
int
bitmap_match(const void *key1, const void *key2, Size keysize)
{
Assert(keysize == sizeof(Bitmapset *));
return !bms_equal(*((const Bitmapset *const *) key1),
*((const Bitmapset *const *) key2));
}
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