1. A device for generating the circular convolution function of two series of values {a.sub.n } and {b.sub.n } said device including: a pair of means, each for generating the primitive root transforms {A.sub.k } or {B.sub.k } respectively of one of said series {a.sub.n } and {b.sub.n } means connected to said pair of means for multiplying term-by-term, the terms of said transforms generated by said pair of means; and a third means of generating a series of terms which are a constant multiple q of the terms of the inverse transform of the series of said products from said multiplying means, said device characterized in that at least one of said pair of means generating said primitive root transforms includes: a. means for building by successive accumulations, multiples of the terms of the associated one of said series; and b. means for building the primitive root transforms of the terms of said associated one of said series by successive and selective accumulations of said multiples.