tonality analysis

Hi,
FFT for calculating tonality in analysis.c file.

    for (i=0;i<N2;i++)
    {
 //Why assign real number(audio sampled points) to image parts for FFT?
       float w = analysis_window[i];
       in[i].r = (kiss_fft_scalar)(w*tonal->inmem[i]);
       in[i].i = (kiss_fft_scalar)(w*tonal->inmem[N2+i]);
       in[N-i-1].r = (kiss_fft_scalar)(w*tonal->inmem[N-i-1]);
       in[N-i-1].i = (kiss_fft_scalar)(w*tonal->inmem[N+N2-i-1]);
    }
and then:
    opus_fft(kfft, in, out, tonal->arch);

tonal->inmem is 10ms smoothed input float point audio data(Total length is 30ms). So Why assign real number(audio sampled points) to image parts for FFT? and what does FFT out spectrum mean? could some one help？

Thanks!

Start in analysis.c at the input preparation loop and the opus_fft(kfft, in, out, tonal->arch) call. Trace the surrounding tonality-analysis code and any existing FFT documentation or tests to establish what the real and imaginary inputs represent and how the output spectrum is used. Done means documenting those points clearly, including the rationale for the assignments.