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

/*-------------------------------------------------------------------------
 *
 * hashfunc.c
 *	  Support functions for hash access method.
 *
 * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/access/hash/hashfunc.c
 *
 * NOTES
 *	  These functions are stored in pg_amproc.  For each operator class
 *	  defined for hash indexes, they compute the hash value of the argument.
 *
 *	  Additional hash functions appear in /utils/adt/ files for various
 *	  specialized datatypes.
 *
 *	  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 joins, for example.  In most cases a hash
 *	  function should use hash_any() or its variant hash_uint32().
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/hash.h"
#include "catalog/pg_collation.h"
#include "common/hashfn.h"
#include "utils/builtins.h"
#include "utils/float.h"
#include "utils/pg_locale.h"
#include "varatt.h"

/*
 * Datatype-specific hash functions.
 *
 * These support both hash indexes and hash joins.
 *
 * NOTE: some of these are also used by catcache operations, without
 * any direct connection to hash indexes.  Also, the common hash_any
 * routine is also used by dynahash tables.
 */

/* Note: this is used for both "char" and boolean datatypes */
Datum
hashchar(PG_FUNCTION_ARGS)
{
	return hash_uint32((int32) PG_GETARG_CHAR(0));
}

Datum
hashcharextended(PG_FUNCTION_ARGS)
{
	return hash_uint32_extended((int32) PG_GETARG_CHAR(0), PG_GETARG_INT64(1));
}

Datum
hashint2(PG_FUNCTION_ARGS)
{
	return hash_uint32((int32) PG_GETARG_INT16(0));
}

Datum
hashint2extended(PG_FUNCTION_ARGS)
{
	return hash_uint32_extended((int32) PG_GETARG_INT16(0), PG_GETARG_INT64(1));
}

Datum
hashint4(PG_FUNCTION_ARGS)
{
	return hash_uint32(PG_GETARG_INT32(0));
}

Datum
hashint4extended(PG_FUNCTION_ARGS)
{
	return hash_uint32_extended(PG_GETARG_INT32(0), PG_GETARG_INT64(1));
}

Datum
hashint8(PG_FUNCTION_ARGS)
{
	/*
	 * The idea here is to produce a hash value compatible with the values
	 * produced by hashint4 and hashint2 for logically equal inputs; this is
	 * necessary to support cross-type hash joins across these input types.
	 * Since all three types are signed, we can xor the high half of the int8
	 * value if the sign is positive, or the complement of the high half when
	 * the sign is negative.
	 */
	int64		val = PG_GETARG_INT64(0);
	uint32		lohalf = (uint32) val;
	uint32		hihalf = (uint32) (val >> 32);

	lohalf ^= (val >= 0) ? hihalf : ~hihalf;

	return hash_uint32(lohalf);
}

Datum
hashint8extended(PG_FUNCTION_ARGS)
{
	/* Same approach as hashint8 */
	int64		val = PG_GETARG_INT64(0);
	uint32		lohalf = (uint32) val;
	uint32		hihalf = (uint32) (val >> 32);

	lohalf ^= (val >= 0) ? hihalf : ~hihalf;

	return hash_uint32_extended(lohalf, PG_GETARG_INT64(1));
}

Datum
hashoid(PG_FUNCTION_ARGS)
{
	return hash_uint32((uint32) PG_GETARG_OID(0));
}

Datum
hashoidextended(PG_FUNCTION_ARGS)
{
	return hash_uint32_extended((uint32) PG_GETARG_OID(0), PG_GETARG_INT64(1));
}

Datum
hashenum(PG_FUNCTION_ARGS)
{
	return hash_uint32((uint32) PG_GETARG_OID(0));
}

Datum
hashenumextended(PG_FUNCTION_ARGS)
{
	return hash_uint32_extended((uint32) PG_GETARG_OID(0), PG_GETARG_INT64(1));
}

Datum
hashfloat4(PG_FUNCTION_ARGS)
{
	float4		key = PG_GETARG_FLOAT4(0);
	float8		key8;

	/*
	 * On IEEE-float machines, minus zero and zero have different bit patterns
	 * but should compare as equal.  We must ensure that they have the same
	 * hash value, which is most reliably done this way:
	 */
	if (key == (float4) 0)
		PG_RETURN_UINT32(0);

	/*
	 * To support cross-type hashing of float8 and float4, we want to return
	 * the same hash value hashfloat8 would produce for an equal float8 value.
	 * So, widen the value to float8 and hash that.  (We must do this rather
	 * than have hashfloat8 try to narrow its value to float4; that could fail
	 * on overflow.)
	 */
	key8 = key;

	/*
	 * Similarly, NaNs can have different bit patterns but they should all
	 * compare as equal.  For backwards-compatibility reasons we force them to
	 * have the hash value of a standard float8 NaN.  (You'd think we could
	 * replace key with a float4 NaN and then widen it; but on some old
	 * platforms, that way produces a different bit pattern.)
	 */
	if (isnan(key8))
		key8 = get_float8_nan();

	return hash_any((unsigned char *) &key8, sizeof(key8));
}

Datum
hashfloat4extended(PG_FUNCTION_ARGS)
{
	float4		key = PG_GETARG_FLOAT4(0);
	uint64		seed = PG_GETARG_INT64(1);
	float8		key8;

	/* Same approach as hashfloat4 */
	if (key == (float4) 0)
		PG_RETURN_UINT64(seed);
	key8 = key;
	if (isnan(key8))
		key8 = get_float8_nan();

	return hash_any_extended((unsigned char *) &key8, sizeof(key8), seed);
}

Datum
hashfloat8(PG_FUNCTION_ARGS)
{
	float8		key = PG_GETARG_FLOAT8(0);

	/*
	 * On IEEE-float machines, minus zero and zero have different bit patterns
	 * but should compare as equal.  We must ensure that they have the same
	 * hash value, which is most reliably done this way:
	 */
	if (key == (float8) 0)
		PG_RETURN_UINT32(0);

	/*
	 * Similarly, NaNs can have different bit patterns but they should all
	 * compare as equal.  For backwards-compatibility reasons we force them to
	 * have the hash value of a standard NaN.
	 */
	if (isnan(key))
		key = get_float8_nan();

	return hash_any((unsigned char *) &key, sizeof(key));
}

Datum
hashfloat8extended(PG_FUNCTION_ARGS)
{
	float8		key = PG_GETARG_FLOAT8(0);
	uint64		seed = PG_GETARG_INT64(1);

	/* Same approach as hashfloat8 */
	if (key == (float8) 0)
		PG_RETURN_UINT64(seed);
	if (isnan(key))
		key = get_float8_nan();

	return hash_any_extended((unsigned char *) &key, sizeof(key), seed);
}

Datum
hashoidvector(PG_FUNCTION_ARGS)
{
	oidvector  *key = (oidvector *) PG_GETARG_POINTER(0);

	return hash_any((unsigned char *) key->values, key->dim1 * sizeof(Oid));
}

Datum
hashoidvectorextended(PG_FUNCTION_ARGS)
{
	oidvector  *key = (oidvector *) PG_GETARG_POINTER(0);

	return hash_any_extended((unsigned char *) key->values,
							 key->dim1 * sizeof(Oid),
							 PG_GETARG_INT64(1));
}

Datum
hashname(PG_FUNCTION_ARGS)
{
	char	   *key = NameStr(*PG_GETARG_NAME(0));

	return hash_any((unsigned char *) key, strlen(key));
}

Datum
hashnameextended(PG_FUNCTION_ARGS)
{
	char	   *key = NameStr(*PG_GETARG_NAME(0));

	return hash_any_extended((unsigned char *) key, strlen(key),
							 PG_GETARG_INT64(1));
}

Datum
hashtext(PG_FUNCTION_ARGS)
{
	text	   *key = PG_GETARG_TEXT_PP(0);
	Oid			collid = PG_GET_COLLATION();
	pg_locale_t mylocale = 0;
	Datum		result;

	if (!collid)
		ereport(ERROR,
				(errcode(ERRCODE_INDETERMINATE_COLLATION),
				 errmsg("could not determine which collation to use for string hashing"),
				 errhint("Use the COLLATE clause to set the collation explicitly.")));

	if (!lc_collate_is_c(collid))
		mylocale = pg_newlocale_from_collation(collid);

	if (pg_locale_deterministic(mylocale))
	{
		result = hash_any((unsigned char *) VARDATA_ANY(key),
						  VARSIZE_ANY_EXHDR(key));
	}
	else
	{
		Size		bsize,
					rsize;
		char	   *buf;
		const char *keydata = VARDATA_ANY(key);
		size_t		keylen = VARSIZE_ANY_EXHDR(key);


		bsize = pg_strnxfrm(NULL, 0, keydata, keylen, mylocale);
		buf = palloc(bsize + 1);

		rsize = pg_strnxfrm(buf, bsize + 1, keydata, keylen, mylocale);
		if (rsize != bsize)
			elog(ERROR, "pg_strnxfrm() returned unexpected result");

		/*
		 * In principle, there's no reason to include the terminating NUL
		 * character in the hash, but it was done before and the behavior must
		 * be preserved.
		 */
		result = hash_any((uint8_t *) buf, bsize + 1);

		pfree(buf);
	}

	/* Avoid leaking memory for toasted inputs */
	PG_FREE_IF_COPY(key, 0);

	return result;
}

Datum
hashtextextended(PG_FUNCTION_ARGS)
{
	text	   *key = PG_GETARG_TEXT_PP(0);
	Oid			collid = PG_GET_COLLATION();
	pg_locale_t mylocale = 0;
	Datum		result;

	if (!collid)
		ereport(ERROR,
				(errcode(ERRCODE_INDETERMINATE_COLLATION),
				 errmsg("could not determine which collation to use for string hashing"),
				 errhint("Use the COLLATE clause to set the collation explicitly.")));

	if (!lc_collate_is_c(collid))
		mylocale = pg_newlocale_from_collation(collid);

	if (pg_locale_deterministic(mylocale))
	{
		result = hash_any_extended((unsigned char *) VARDATA_ANY(key),
								   VARSIZE_ANY_EXHDR(key),
								   PG_GETARG_INT64(1));
	}
	else
	{
		Size		bsize,
					rsize;
		char	   *buf;
		const char *keydata = VARDATA_ANY(key);
		size_t		keylen = VARSIZE_ANY_EXHDR(key);

		bsize = pg_strnxfrm(NULL, 0, keydata, keylen, mylocale);
		buf = palloc(bsize + 1);

		rsize = pg_strnxfrm(buf, bsize + 1, keydata, keylen, mylocale);
		if (rsize != bsize)
			elog(ERROR, "pg_strnxfrm() returned unexpected result");

		/*
		 * In principle, there's no reason to include the terminating NUL
		 * character in the hash, but it was done before and the behavior must
		 * be preserved.
		 */
		result = hash_any_extended((uint8_t *) buf, bsize + 1,
								   PG_GETARG_INT64(1));

		pfree(buf);
	}

	PG_FREE_IF_COPY(key, 0);

	return result;
}

/*
 * 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_PP(0);
	Datum		result;

	result = hash_any((unsigned char *) VARDATA_ANY(key),
					  VARSIZE_ANY_EXHDR(key));

	/* Avoid leaking memory for toasted inputs */
	PG_FREE_IF_COPY(key, 0);

	return result;
}

Datum
hashvarlenaextended(PG_FUNCTION_ARGS)
{
	struct varlena *key = PG_GETARG_VARLENA_PP(0);
	Datum		result;

	result = hash_any_extended((unsigned char *) VARDATA_ANY(key),
							   VARSIZE_ANY_EXHDR(key),
							   PG_GETARG_INT64(1));

	PG_FREE_IF_COPY(key, 0);

	return result;
}