def write_longlong(self, n, pack=Struct('>Q').pack):
        """
        Write an integer as an unsigned 64-bit value.
        """
        if 0 <= n <= 0xFFFFFFFFFFFFFFFF:
            self._output_buffer.extend(pack(n))
        else:
            raise ValueError(
                'Longlong %d out of range 0..0xFFFFFFFFFFFFFFFF', n)
        return self
Write an integer as an unsigned 64-bit value.