public long nextLong() {
      if (!hasNext()) {
        throw new NoSuchElementException();
      }
      c--;
      if (mustReturnNull) {
        mustReturnNull = false;
        return keys[n];
      }
      long[] key = StrippedLongSet.this.keys;
      for (; ; ) {
        long v = key[--pos];
        if (v != 0) {
          return v;
        }
      }
    }
public long nextLong()