A decoding apparatus for decoding digital video data, comprising: a data memory comprising registers, each register being capable of storing a data strings comprising a plurality of data sub-strings such that the data sub-strings are not individually addressable; an input for receiving compressed video information represented by a matrix of data values and loading each data value in order into a respective one of the sub-strings; and processing means for performing an inverse zigzag operation on the matrix of data values by executing a series of reordering operations on the data strings to reorder the data sub-strings comprised therein.