pub unsafe extern "C" fn fftw_plan_guru64_r2r(
rank: c_int,
dims: *const fftw_iodim64,
howmany_rank: c_int,
howmany_dims: *const fftw_iodim64,
in_: *mut f64,
out: *mut f64,
kind: *const fftw_r2r_kind,
flags: c_uint,
) -> fftw_plan