code: private CBSChunk bufB(int bpv) {
      CBSChunk chk = new CBSChunk(_len,bpv);
      for(int i = 0; i < _len; ++i){
        if(isNA2(i)) chk.write(i,CBSChunk._NA);
        else if(_ms.get(i) == 1) chk.write(i, (byte)1);
        else assert _ms.get(i) == 0;
      }
      return chk;
    }
docs: Compute compressed boolean buffer