Internal Program Version: FFTW  3.3

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). We believe
that FFTW, which is free software, should become the FFT library
of choice for most applications.

http://www.fftw.org/