Java Programming

Hi,

I have to program a invers fast fourier transform, therefore i read some papers and asserted, that
the radix-N-Algorithms are the fastest available.

But they only work for input that is a power of 2 :-(

My input isnt a power of two, so i thought i could possibly expand my array from 108 to 128 and could use the radix-2-algorihm.
But unfortunatly on this way i'm affecting the calculation method and the result is always incorrect because i expand on the false way.

Can anyone tell me how i have to expand my array, so that the calculation isnt affected ?

( or can anyone tell me where to finde a java algorithm for the inverse fourier transform for arbitrary n? )

Thanks a lot !