Function array_get_slice

src/backend/utils/adt/arrayfuncs.c:2043–2180

* array_get_slice : * This routine takes an array and a range of indices (upperIndx and * lowerIndx), creates a new array structure for the referred elements * and returns a pointer to it. * * This handles both ordinary varlena arrays and fixed-length arrays. * * Inputs: * arraydatum: the array object (mustn't be NULL) * nSubscripts: number of subscripts supplied (must be same

 * even when nSubscripts is less.  These are generally just temporaries.
 */
Datum
array_get_slice(Datum arraydatum,
				int nSubscripts,
				int *upperIndx,
				int *lowerIndx,
				bool *upperProvided,
				bool *lowerProvided,
				int arraytyplen,
				int elmlen,
				bool elmbyval,
				char elmalign)
{
	ArrayType  *array;
	ArrayType  *newarray;
	int			i,
				ndim,
			   *dim,
			   *lb,
			   *newlb;
	int			fixedDim[1],
				fixedLb[1];
	Oid			elemtype;
	char	   *arraydataptr;
	bits8	   *arraynullsptr;
	int32		dataoffset;
	int			bytes,
				span[MAXDIM];

	if (arraytyplen > 0)
	{
		/*
		 * fixed-length arrays -- currently, cannot slice these because parser
		 * labels output as being of the fixed-length array type! Code below
		 * shows how we could support it if the parser were changed to label
		 * output as a suitable varlena array type.
		 */
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("slices of fixed-length arrays not implemented")));

		/*
		 * fixed-length arrays -- these are assumed to be 1-d, 0-based
		 *
		 * XXX where would we get the correct ELEMTYPE from?
		 */
		ndim = 1;
		fixedDim[0] = arraytyplen / elmlen;
		fixedLb[0] = 0;
		dim = fixedDim;
		lb = fixedLb;
		elemtype = InvalidOid;	/* XXX */
		arraydataptr = (char *) DatumGetPointer(arraydatum);
		arraynullsptr = NULL;
	}
	else
	{
		/* detoast input array if necessary */
		array = DatumGetArrayTypeP(arraydatum);