postgresql/src/backend/access/hash/hashfunc.c

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/*-------------------------------------------------------------------------
*
* hashfunc.c
* Comparison functions for hash access method.
*
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/access/hash/hashfunc.c,v 1.26 2000/06/05 07:28:35 tgl 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
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)));
}
/* Hash function from Chris Torek. */
Datum
hashfloat4(PG_FUNCTION_ARGS)
{
float4 key = PG_GETARG_FLOAT4(0);
char *kp = (char *) &key;
int len = sizeof(key);
int loop;
uint32 h;
#define HASH4a h = (h << 5) - h + *kp++;
#define HASH4b h = (h << 5) + h + *kp++;
#define HASH4 HASH4b
h = 0;
/*
* This is a tad silly, given that we expect len = 4, but a smart
* compiler should be able to eliminate the redundant code...
*/
loop = (len + 8 - 1) >> 3;
switch (len & (8 - 1))
{
case 0:
do
{ /* All fall throughs */
HASH4;
case 7:
HASH4;
case 6:
HASH4;
case 5:
HASH4;
case 4:
HASH4;
case 3:
HASH4;
case 2:
HASH4;
case 1:
HASH4;
} while (--loop);
}
PG_RETURN_UINT32(h);
}
Datum
hashfloat8(PG_FUNCTION_ARGS)
{
float8 key = PG_GETARG_FLOAT8(0);
char *kp = (char *) &key;
int len = sizeof(key);
int loop;
uint32 h;
#define HASH4a h = (h << 5) - h + *kp++;
#define HASH4b h = (h << 5) + h + *kp++;
#define HASH4 HASH4b
h = 0;
/*
* This is a tad silly, given that we expect len = 8, but a smart
* compiler should be able to eliminate the redundant code...
*/
loop = (len + 8 - 1) >> 3;
switch (len & (8 - 1))
{
case 0:
do
{ /* All fall throughs */
HASH4;
case 7:
HASH4;
case 6:
HASH4;
case 5:
HASH4;
case 4:
HASH4;
case 3:
HASH4;
case 2:
HASH4;
case 1:
HASH4;
} while (--loop);
}
PG_RETURN_UINT32(h);
}
Datum
hashoid(PG_FUNCTION_ARGS)
{
PG_RETURN_UINT32(~(uint32) PG_GETARG_OID(0));
}
Datum
hashoidvector(PG_FUNCTION_ARGS)
{
Oid *key = (Oid *) PG_GETARG_POINTER(0);
int i;
uint32 result = 0;
for (i = INDEX_MAX_KEYS; --i >= 0;)
result = (result << 1) ^ (~(uint32) key[i]);
PG_RETURN_UINT32(result);
}
/*
* 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);
int i;
uint32 result = 0;
for (i = INDEX_MAX_KEYS; --i >= 0;)
result = (result << 1) ^ (~(uint32) key[i]);
PG_RETURN_UINT32(result);
}
#define PRIME1 37
#define PRIME2 1048583
Datum
hashchar(PG_FUNCTION_ARGS)
{
uint32 h;
/* Convert char to integer */
h = (PG_GETARG_CHAR(0) - ' ');
h %= PRIME2;
PG_RETURN_UINT32(h);
}
Datum
hashname(PG_FUNCTION_ARGS)
{
char *key = NameStr(* PG_GETARG_NAME(0));
int len = NAMEDATALEN;
uint32 h;
h = 0;
/* Convert string to integer */
while (len--)
h = h * PRIME1 ^ (*key++ - ' ');
h %= PRIME2;
PG_RETURN_UINT32(h);
}
/*
* (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 other 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
hashtext(PG_FUNCTION_ARGS)
{
text *key = PG_GETARG_TEXT_P(0);
int keylen;
char *keydata;
uint32 n;
int loop;
keydata = VARDATA(key);
keylen = VARSIZE(key) - VARHDRSZ;
#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);
}
}
PG_RETURN_UINT32(n);
}