def write_longlong(self, n):
        """
        Write an integer as an unsigned 64-bit value.

        """
        if (n < 0) or (n >= (2**64)):
            raise ValueError('Octet out of range 0..2**64-1')
        self._flushbits()
        self.out.write(pack('>Q', n))
Write an integer as an unsigned 64-bit value.