SRFFT - CONCEPT
Exploits both RAD2 and RAD4 frameworks
Divides an N-point DFT computation into a N/2 point DFT and two N/4 point DFTs
RAD2 used to compute the N/2 point FFT to give the even DFT points
RAD4 used to compute the N/4 point FFT to give the odd DFT points