A method of processing a set of input data values comprises the steps of providing said input data values serially to circuitry comprising a number of memory elements; and performing in said circuitry a transform function to obtain a set of transformed data values. The method further comprises the steps of delaying a subset of said set of input data values under use of said memory elements; providing a modified set of data values by adding individual delayed data values to individual non-delayed data values from said set of input data values; and performing said transform function on said modified set of data values. In this way a transform function can be evaluated at fewer output data values than available input data values without increasing the memory requirements considerably.