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Hello,

I'm implementing a autocorrelation function using a fft and ifft hard core (v6.0) on a Virtex5. When starting the fft, I see at the output that the result is reversed in the frequency domain.

Example: The input signal is a sinus with a frequency of 2 Hz. As output signal I expect a dirac impuls at the beginning (imaginary).
-> f(0)=0; f(1)=0; f(2)=1; f(3)=0; …; f(N-3)=0; f(N-2)=-1; f(N-1)=0; f(N)=0; (*)

But I get:
-> f(0)=0; f(1)=0; f(2)=-1; f(3)=0; …; f(N-3)=0; f(N-2)=1; f(N-1)=0; f(N)=0;

Other input signals also get the same result, that the output is reversed.
Can you please explain me why the output order is reversed? I have no explanation!
Is it possible to reorder the output signal like (*)?

Best regards,
Kris