docs: public static long andNotCount(OpenBitSet a, OpenBitSet b) {
          long tot = BitUtil.pop_andnot( a.bits, b.bits, 0, Math.min( a.wlen, b.wlen ) );
          if (a.wlen > b.wlen) {
              tot += BitUtil.pop_array( a.bits, b.wlen, a.wlen - b.wlen );
          }
          return tot;
      }