code: func (ba *bitArray) complement() {
  	for i := uint64(0); i < uint64(len(ba.blocks)); i++ {
  		ba.blocks[i] = ^ba.blocks[i]
  	}
  
  	ba.setLowest()
  	if ba.anyset {
  		ba.setHighest()
  	}
  }
docs: // complement flips all bits in this array.