pub unsafe extern "C" fn secp256k1_ellswift_xdh(
    ctx: *const Context,
    output: *mut c_uchar,
    ell_a64: *const c_uchar,
    ell_b64: *const c_uchar,
    seckey32: *const c_uchar,
    party: c_int,
    hashfp: EllswiftEcdhHashFn,
    data: *mut c_void
) -> c_int