1. In a signal processor for performing a discrete Fast Fourier Transform on signals applied to such signal processor, such processor including apparatus for repetitively performing the algebraic sum of AW and B, where A is a first portion of such signals, W is a scaling factor and B is a second, later portion of such signals, such apparatus comprising: (a) means for converting the first portion of such signals, A, into a first series of binary digits; (b) serial-parallel multiplier means for multiplying the first series of binary digits by a digital word of N bits representative of the scale factor W and fed in parallel to the multiplier means to form the product AW, such product being produced by such multiplier means as a second series of binary digits; (c) decoder means responsive to a third series of binary digits representative of the second portion of such signals, B, and to the second series of binary digits representative of the product, AW, to form the algebraic sum of AW and B, such sum being produced by such decoder means as a series of binary digits.