FFT Kernels

Hi everybody,

quick question:

https://software.intel.com/en-us/articles/fft-length-and-layout-advisor

states: "The Intel® MKL FFT implementation employs radix 2, 3, 4, 5, 7, 8, 11, 13, 16 kernels, and several other larger size kernels."

https://software.intel.com/en-us/articles/mkl-ipp-choosing-an-fft

states: "2,3,5,7,11 and 13 kernels (**) ** - Both libraries support arbitrary radix in optimized manner, that is O(N log N), but these specific radixes are better optimized than others. 

So are only the radixes 2,3,5,7,11 and 13 optimized or 2, 3, 4, 5, 7, 8, 11, 13, 16 and several other? I do not find the answer to that anywhere. And before I start optimizing and get a suboptimal result (because I didn't know better) - I thought I'd ask.

Thanks!

Lui