TITLE: Non-power-of-2 FFT's?
QUESTION [39 upvotes]: If I have a program that can compute FFT's for sizes that are powers of 2, how can I use it to compute FFT's for other sizes?
I have read that I can supposedly zero-pad the original points, but I'm lost as to how this gives me the correct answer. If I transform a function with 5 points, I expect to get back a 5-point DFT, and I don't understand how I can extract that from the 8-point DFT (which was calculated with zero-padding).

REPLY [2 votes]: Are you aware of FFTW?  It's been available for free for years; I have used it and can attest to its ease of use and speed.