FFT on complex units
Real-optimized FFTs (returns the positive half-spectrum: (nfft/2+1) complex frequency bins) The real (i.e. not complex) optimization code only works for even length ffts. It does two half-length FFTs in parallel (packed into real&imag), and then combines them via twiddling. The result is nfft/2+1 complex frequency bins from DC to Nyquist. If you don’t know what this means, search the web because neither do I.
! Rust wrapper around KissFFT. Represents a FFT direction.