pub unsafe extern "C" fn ecdsa_write_signature_restartable(
    ctx: *mut ecdsa_context,
    md_alg: md_type_t,
    hash: *const c_uchar,
    hlen: size_t,
    sig: *mut c_uchar,
    slen: *mut size_t,
    f_rng: Option<unsafe extern "C" fn(arg1: *mut c_void, arg2: *mut c_uchar, arg3: size_t) -> c_int>,
    p_rng: *mut c_void,
    rs_ctx: *mut ecdsa_restart_ctx
) -> c_int