Протестировал FFT128real32.zip - 32 bit real FFT 128 points + windowing + magnitude (IAR, Keil, gcc) из Embedded Signals на RTL00.
Window16to32b_real( x, Hamming128_16b, N); // perform windowing function
[N] тактов:
[128] 1012, [1024] 7732, [2048] 15412, [4096] 30772
FFT128Real_32b(y,x); //...