pub unsafe extern "C" fn fftwf_plan_guru64_r2r(
    rank: c_int,
    dims: *const fftwf_iodim64,
    howmany_rank: c_int,
    howmany_dims: *const fftwf_iodim64,
    in_: *mut f32,
    out: *mut f32,
    kind: *const fftwf_r2r_kind,
    flags: c_uint
) -> fftwf_plan