Function hash_array_extended

src/backend/utils/adt/arrayfuncs.c:4180–4253

* Returns 64-bit value by hashing a value to a 64-bit value, with a seed. * Otherwise, similar to hash_array. */

 * Otherwise, similar to hash_array.
 */
Datum
hash_array_extended(PG_FUNCTION_ARGS)
{
	LOCAL_FCINFO(locfcinfo, 2);
	AnyArrayType *array = PG_GETARG_ANY_ARRAY_P(0);
	uint64		seed = PG_GETARG_INT64(1);
	int			ndims = AARR_NDIM(array);
	int		   *dims = AARR_DIMS(array);
	Oid			element_type = AARR_ELEMTYPE(array);
	uint64		result = 1;
	int			nitems;
	TypeCacheEntry *typentry;
	int			typlen;
	bool		typbyval;
	char		typalign;
	int			i;
	array_iter	iter;

	typentry = (TypeCacheEntry *) fcinfo->flinfo->fn_extra;
	if (typentry == NULL ||
		typentry->type_id != element_type)
	{
		typentry = lookup_type_cache(element_type,
									 TYPECACHE_HASH_EXTENDED_PROC_FINFO);
		if (!OidIsValid(typentry->hash_extended_proc_finfo.fn_oid))
			ereport(ERROR,
					(errcode(ERRCODE_UNDEFINED_FUNCTION),
					 errmsg("could not identify an extended hash function for type %s",
							format_type_be(element_type))));
		fcinfo->flinfo->fn_extra = (void *) typentry;
	}
	typlen = typentry->typlen;
	typbyval = typentry->typbyval;
	typalign = typentry->typalign;

	InitFunctionCallInfoData(*locfcinfo, &typentry->hash_extended_proc_finfo, 2,
							 PG_GET_COLLATION(), NULL, NULL);

	/* Loop over source data */
	nitems = ArrayGetNItems(ndims, dims);
	array_iter_setup(&iter, array);

	for (i = 0; i < nitems; i++)
	{
		Datum		elt;
		bool		isnull;
		uint64		elthash;

		/* Get element, checking for NULL */
		elt = array_iter_next(&iter, &isnull, i, typlen, typbyval, typalign);

		if (isnull)
		{
			elthash = 0;
		}
		else
		{
			/* Apply the hash function */