Function std::fft_real_half

int fft_real_half([]const double in, []Complex out)

Only the n/2 + 1 non-redundant bins (0 .. n/2) of fft_real, the rest being their conjugates: half the output to write. out holds n/2 + 1 values; in the batch, row r's bins start at out[r * (n/2 + 1)].