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/*-------------------------------------------------------------------------
*
* hashfunc.c
* Comparison functions for hash access method.
*
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/access/hash/hashfunc.c,v 1.30 2001/03/22 03:59:13 momjian Exp $
*
* NOTES
* These functions are stored in pg_amproc. For each operator class
* defined on hash tables, they compute the hash value of the argument.
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/hash.h"
Datum
hashchar(PG_FUNCTION_ARGS)
{
PG_RETURN_UINT32(~((uint32) PG_GETARG_CHAR(0)));
}
Datum
hashint2(PG_FUNCTION_ARGS)
{
PG_RETURN_UINT32(~((uint32) PG_GETARG_INT16(0)));
}
Datum
hashint4(PG_FUNCTION_ARGS)
{
PG_RETURN_UINT32(~PG_GETARG_UINT32(0));
}
Datum
hashint8(PG_FUNCTION_ARGS)
{
/* we just use the low 32 bits... */
PG_RETURN_UINT32(~((uint32) PG_GETARG_INT64(0)));
}
Datum
hashoid(PG_FUNCTION_ARGS)
{
PG_RETURN_UINT32(~((uint32) PG_GETARG_OID(0)));
}
Datum
hashfloat4(PG_FUNCTION_ARGS)
{
float4 key = PG_GETARG_FLOAT4(0);
return hash_any((char *) &key, sizeof(key));
}
Datum
hashfloat8(PG_FUNCTION_ARGS)
{
float8 key = PG_GETARG_FLOAT8(0);
return hash_any((char *) &key, sizeof(key));
}
Datum
hashoidvector(PG_FUNCTION_ARGS)
{
Oid *key = (Oid *) PG_GETARG_POINTER(0);
return hash_any((char *) key, INDEX_MAX_KEYS * sizeof(Oid));
}
/*
* Note: hashint2vector currently can't be used as a user hash table
* hash function, because it has no pg_proc entry. We only need it
* for catcache indexing.
*/
Datum
hashint2vector(PG_FUNCTION_ARGS)
{
int16 *key = (int16 *) PG_GETARG_POINTER(0);
return hash_any((char *) key, INDEX_MAX_KEYS * sizeof(int16));
}
Datum
hashname(PG_FUNCTION_ARGS)
{
char *key = NameStr(*PG_GETARG_NAME(0));
return hash_any((char *) key, NAMEDATALEN);
}
/*
* hashvarlena() can be used for any varlena datatype in which there are
* no non-significant bits, ie, distinct bitpatterns never compare as equal.
*/
Datum
hashvarlena(PG_FUNCTION_ARGS)
{
struct varlena *key = PG_GETARG_VARLENA_P(0);
Datum result;
result = hash_any(VARDATA(key), VARSIZE(key) - VARHDRSZ);
/* Avoid leaking memory for toasted inputs */
PG_FREE_IF_COPY(key, 0);
return result;
}
/*
* hash_any --- compute a hash function for any specified chunk of memory
*
* This can be used as the underlying hash function for any pass-by-reference
* data type in which there are no non-significant bits.
*
* (Comment from the original db3 hashing code: )
*
* "This is INCREDIBLY ugly, but fast. We break the string up into 8 byte
* units. On the first time through the loop we get the 'leftover bytes'
* (strlen % 8). On every later iteration, we perform 8 HASHC's so we handle
* all 8 bytes. Essentially, this saves us 7 cmp & branch instructions. If
* this routine is heavily used enough, it's worth the ugly coding.
*
* "OZ's original sdbm hash"
*/
Datum
hash_any(char *keydata, int keylen)
{
uint32 n;
int loop;
#define HASHC n = *keydata++ + 65599 * n
n = 0;
if (keylen > 0)
{
loop = (keylen + 8 - 1) >> 3;
switch (keylen & (8 - 1))
{
case 0:
do
{ /* All fall throughs */
HASHC;
case 7:
HASHC;
case 6:
HASHC;
case 5:
HASHC;
case 4:
HASHC;
case 3:
HASHC;
case 2:
HASHC;
case 1:
HASHC;
} while (--loop);
}
}
#undef HASHC
PG_RETURN_UINT32(n);
}
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