code: private Chunk chunkUUID() {
      final byte [] bs = MemoryManager.malloc1(_len *16,true);
      int j = 0;
      for( int i = 0; i < _len; ++i ) {
        long lo = 0, hi=0;
        if( _id == null || _id.length == 0 || (j < _id.length && _id[j] == i ) ) {
          if(_missing != null && _missing.get(j)) {
            lo = C16Chunk._LO_NA;
            hi = C16Chunk._HI_NA;
          } else {
            lo = _ms.get(j);
            hi = Double.doubleToRawLongBits(_ds[j]);
          }
          j++;
        }
        UnsafeUtils.set8(bs, 16*i  , lo);
        UnsafeUtils.set8(bs, 16 * i + 8, hi);
      }
      assert j == _sparseLen :"j = " + j + ", _sparselen = " + _sparseLen;
      return new C16Chunk(bs);
    }
docs: Compute a compressed UUID buffer