code: func (s *rowSegment) Merge(other *rowSegment) {
  	s.ensureWritable()
  
  	itr := other.data.Iterator()
  	for v, eof := itr.Next(); !eof; v, eof = itr.Next() {
  		s.SetBit(v)
  	}
  }
docs: // Merge adds chunks from other to s.
  // Chunks in s are overwritten if they exist in other.