Add some windowing algorithms?

[jerabaul29]

I see that only the "pure" FFT is available, no windowing algorithm. Do you think it would be ok to add a small kiss_windowing.h/cpp to provide a bit of windowing ability (maybe a few of the more common, hann, hamming, would be great :) ).

[marcusmueller]

As a user of KISS FFT, I'd personally rather keep the library simple. There's no computational advantage of integrating windowing functions into a FFT library, so using a separate library, especially if it's just a header, would be wiser, in my humble opinion.