public static extern fftw_plan fftw_plan_guru_dft_c2r(int rank, ref fftw_iodim dims,
int batch_rank, ref fftw_iodim batch_dims,
ref fftw_complex _in, ref double _out,
uint flags);
public static extern fftw_plan fftw_plan_guru_dft(int rank, ref fftw_iodim dims,
int batch_rank, ref fftw_iodim batch_dims,
ref fftw_complex _in, ref fftw_complex _out,
int sign, uint flags);