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DFT data layout

CCS format:

index real imaginary
0 frequency[0].real() (DC offset) always 0 because of real input
1 frequency[1].real() frequency[1].imag()
N/2-1 frequency[N/2-1].real() frequency[N/2-1].imag()
N/2 frequency[N/2].real() (Nyquist frequency) always 0 because of real input

Perm format:

index real imaginary
0 frequency[0].real() (DC offset) frequency[N/2].real() (Nyquist frequency)
1 frequency[1].real() frequency[1].imag()
N/2-1 frequency[N/2-1].real() frequency[N/2-1].imag()