FFTW

FFTW is a C subroutine library for computing the discrete Fourier transform (DFT) in one or more dimensions, of arbitrary input size, and of both real and complex data (as well as of even/odd data, i.e.

the discrete cosine/sine transforms or DCT/DST). Developers believe that FFTW, which is free software, should become the FFT library of choice for most applications.