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/*-------------------------------------------------------------------------
*
* hashfunc.c
* Comparison functions for hash access method.
*
* Portions Copyright (c) 1996-2002, 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 1.35 2002/09/04 20:31:09 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((unsigned char *) &key, sizeof(key));
}
Datum
hashfloat8(PG_FUNCTION_ARGS)
{
float8 key = PG_GETARG_FLOAT8(0);
return hash_any((unsigned char *) &key, sizeof(key));
}
Datum
hashoidvector(PG_FUNCTION_ARGS)
{
Oid *key = (Oid *) PG_GETARG_POINTER(0);
return hash_any((unsigned 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((unsigned char *) key, INDEX_MAX_KEYS * sizeof(int16));
}
Datum
hashname(PG_FUNCTION_ARGS)
{
char *key = NameStr(*PG_GETARG_NAME(0));
int keylen = strlen(key);
Assert(keylen < NAMEDATALEN); /* else it's not truncated
* correctly */
return hash_any((unsigned char *) key, keylen);
}
/*
* 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((unsigned char *) VARDATA(key),
VARSIZE(key) - VARHDRSZ);
/* Avoid leaking memory for toasted inputs */
PG_FREE_IF_COPY(key, 0);
return result;
}
/*
* This hash function was written by Bob Jenkins
* (bob_jenkins@burtleburtle.net), and superficially adapted
* for PostgreSQL by Neil Conway. For more information on this
* hash function, see http://burtleburtle.net/bob/hash/doobs.html,
* or Bob's article in Dr. Dobb's Journal, Sept. 1997.
*/
/*----------
* mix -- mix 3 32-bit values reversibly.
* For every delta with one or two bits set, and the deltas of all three
* high bits or all three low bits, whether the original value of a,b,c
* is almost all zero or is uniformly distributed,
* - If mix() is run forward or backward, at least 32 bits in a,b,c
* have at least 1/4 probability of changing.
* - If mix() is run forward, every bit of c will change between 1/3 and
* 2/3 of the time. (Well, 22/100 and 78/100 for some 2-bit deltas.)
*----------
*/
#define mix(a,b,c) \
{ \
a -= b; a -= c; a ^= (c>>13); \
b -= c; b -= a; b ^= (a<<8); \
c -= a; c -= b; c ^= (b>>13); \
a -= b; a -= c; a ^= (c>>12); \
b -= c; b -= a; b ^= (a<<16); \
c -= a; c -= b; c ^= (b>>5); \
a -= b; a -= c; a ^= (c>>3); \
b -= c; b -= a; b ^= (a<<10); \
c -= a; c -= b; c ^= (b>>15); \
}
/*
* hash_any() -- hash a variable-length key into a 32-bit value
* k : the key (the unaligned variable-length array of bytes)
* len : the length of the key, counting by bytes
*
* Returns a uint32 value. Every bit of the key affects every bit of
* the return value. Every 1-bit and 2-bit delta achieves avalanche.
* About 6*len+35 instructions. The best hash table sizes are powers
* of 2. There is no need to do mod a prime (mod is sooo slow!).
* If you need less than 32 bits, use a bitmask.
*/
Datum
hash_any(register const unsigned char *k, register int keylen)
{
register uint32 a,
b,
c,
len;
/* Set up the internal state */
len = keylen;
a = b = 0x9e3779b9; /* the golden ratio; an arbitrary value */
c = 3923095; /* initialize with an arbitrary value */
/* handle most of the key */
while (len >= 12)
{
a += (k[0] + ((uint32) k[1] << 8) + ((uint32) k[2] << 16) + ((uint32) k[3] << 24));
b += (k[4] + ((uint32) k[5] << 8) + ((uint32) k[6] << 16) + ((uint32) k[7] << 24));
c += (k[8] + ((uint32) k[9] << 8) + ((uint32) k[10] << 16) + ((uint32) k[11] << 24));
mix(a, b, c);
k += 12;
len -= 12;
}
/* handle the last 11 bytes */
c += keylen;
switch (len) /* all the case statements fall through */
{
case 11:
c += ((uint32) k[10] << 24);
case 10:
c += ((uint32) k[9] << 16);
case 9:
c += ((uint32) k[8] << 8);
/* the first byte of c is reserved for the length */
case 8:
b += ((uint32) k[7] << 24);
case 7:
b += ((uint32) k[6] << 16);
case 6:
b += ((uint32) k[5] << 8);
case 5:
b += k[4];
case 4:
a += ((uint32) k[3] << 24);
case 3:
a += ((uint32) k[2] << 16);
case 2:
a += ((uint32) k[1] << 8);
case 1:
a += k[0];
/* case 0: nothing left to add */
}
mix(a, b, c);
/* report the result */
return UInt32GetDatum(c);
}
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