A method of operating a data-processing unit to produce a transform comprises calculating first and second output data values based at least on first and second input data values. The method comprises reading the first and second input data values from locations of a first buffer, the locations being determined by first and second read addresses based on first and second read indices. The method also comprises writing the first and second output data values to adjacent memory locations of a second buffer during a single write cycle. Furthermore, the method comprises reading third and fourth input data values from locations of the second buffer, the locations being determined by third and fourth read addresses determined by swapping at least two of the bits of the first and second read indices respectively. A data-processing unit for producing a transform, a transform-computation unit and an electronic apparatus are also described.