may be my work on FFT can help you:
"FFT system C project - 8 point FFT using DIT algorithm.
This projects implements an eight point Decimation In Time Fast Fourier Transform.
The internal data buses width and representation will be discussed and explained FFT design consideration .
Twiddle factors representation is also described. For instance for the third stage FFT calculation, fractional numbers are required such as .070710678.see FFT Twiddle Factors
..."
**broken link removed**