def extraBits(self, index):
        """Indicate how many extra bits are needed to interpret symbol
        >>> d = DistanceAlphabet('D', NPOSTFIX=2, NDIRECT=10)
        >>> [d[i].extraBits() for i in range(26)]
        [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
        >>> [d[i].extraBits() for i in range(26,36)]
        [1, 1, 1, 1, 1, 1, 1, 1, 2, 2]
        """
        if index<16+self.NDIRECT: return 0
        return 1 + ((index - self.NDIRECT - 16) >> (self.NPOSTFIX + 1))