code: public final boolean isNA(long i) {
      long x = i - (_start>0 ? _start : 0);
      if( 0 <= x && x < _len ) return isNA0((int)x);
      throw new ArrayIndexOutOfBoundsException(getClass().getSimpleName() + " " +_start+" <= "+i+" < "+(_start+_len));
    }
docs: Fetch the missing-status the slow way.