code: public int cardinality() {
  		int sum = 0;
  		for (int i = 0; i < wordsInUse; i++)
  			sum += Long.bitCount(words[i]);
  		return sum;
  	}
docs: Returns the number of bits set to <tt>true</tt> in this
  <code>BitSet</code>.
  
  @return  the number of bits set to <tt>true</tt> in this
  <code>BitSet</code>.
  @since   1.4