Function array_extract_slice

src/backend/utils/adt/arrayfuncs.c:4986–5044

* Extract a slice of an array into consecutive elements in the destination * array. * * We assume the caller has verified that the slice coordinates are valid, * allocated enough storage for the result, and initialized the header * of the new array. */

 * of the new array.
 */
static void
array_extract_slice(ArrayType *newarray,
					int ndim,
					int *dim,
					int *lb,
					char *arraydataptr,
					bits8 *arraynullsptr,
					int *st,
					int *endp,
					int typlen,
					bool typbyval,
					char typalign)
{
	char	   *destdataptr = ARR_DATA_PTR(newarray);
	bits8	   *destnullsptr = ARR_NULLBITMAP(newarray);
	char	   *srcdataptr;
	int			src_offset,
				dest_offset,
				prod[MAXDIM],
				span[MAXDIM],
				dist[MAXDIM],
				indx[MAXDIM];
	int			i,
				j,
				inc;

	src_offset = ArrayGetOffset(ndim, dim, lb, st);
	srcdataptr = array_seek(arraydataptr, 0, arraynullsptr, src_offset,
							typlen, typbyval, typalign);
	mda_get_prod(ndim, dim, prod);
	mda_get_range(ndim, span, st, endp);
	mda_get_offset_values(ndim, dist, prod, span);
	for (i = 0; i < ndim; i++)
		indx[i] = 0;
	dest_offset = 0;
	j = ndim - 1;
	do
	{
		if (dist[j])
		{
			/* skip unwanted elements */
			srcdataptr = array_seek(srcdataptr, src_offset, arraynullsptr,
									dist[j],
									typlen, typbyval, typalign);
			src_offset += dist[j];
		}
		inc = array_copy(destdataptr, 1,
						 srcdataptr, src_offset, arraynullsptr,
						 typlen, typbyval, typalign);
		if (destnullsptr)
			array_bitmap_copy(destnullsptr, dest_offset,
							  arraynullsptr, src_offset,
							  1);
		destdataptr += inc;
		srcdataptr += inc;
		src_offset++;
		dest_offset++;
	} while ((j = mda_next_tuple(ndim, indx, span)) != -1);