er</span></code> to the Adler-32 checksum of all
          output produced so far (that is, <code class="computeroutput"><span class="identifier">zs</span><span class="special">.</span><span class="identifier">total_out</span>
          <span class="identifier">bytes</span></code>) and returns no error,
          <code class="computeroutput"><span class="identifier">error</span><span class="special">::</span><span class="identifier">end_of_stream</span></code>, or an error code as described
          below.