code: private int reverseHash(String str) {
      int hash = 0;
      int len = str.length();
      for (int i = 0; i < _block; i++) {
        char c = str.charAt(len - i - 1);
        hash = A * hash + CHAR_HASHES[c];
      }
      return hash;
    }
docs: Take rolling hash of last 'block' characters. Start from the end of the string.
  @param str
  @return