code: public boolean isInZeroBlock(int ch) 
      {
          // valid, uncompacted trie and valid c?
          if (m_isCompacted_ || ch > UCharacter.MAX_VALUE 
              || ch < UCharacter.MIN_VALUE) {
              return true;
          }
      
          return m_index_[ch >> SHIFT_] == 0;
      }
docs: Checks if the character belongs to a zero block in the trie
  @param ch codepoint which data is to be retrieved
  @return true if ch is in the zero block