An apparatus includes an input node, an output node, and successive butterfly elements connected between the input node and the output node. Each butterfly element includes a first branch and a second branch that are cross-coupled with each other and that perform, collectively, sample add and sample delay operations. Either the first branch or the second branch of each butterfly element performs a sample inversion, such that a pattern of the sample inversions across the butterfly elements encodes into the butterfly elements a pattern of negative and positive binary values of a particular row of a Prometheus Orthonormal Sets (PONS) matrix. As a result, the successive butterfly elements correlate input samples applied to the input node against the particular row of the PONS matrix as the input samples are shifted through the successive butterfly elements.