A transform is defined in the Galois field of

elements

, a finite field analogous to the field of complex numbers, when

is a prime such that (--1) is not a quadratic residue. It is shown that the action of this transform over

is equivalent to the discrete Fourier transform of a sequence of complex integers of finite dynamic range. If

is a Mersenne prime, one can utilize the fast Fourier transform (FFT) algorithm to yield a fast convolution without the usual roundoff problem of complex numbers.