def intersection!(bitfield)
      raise "That's not a bitfield" if ! bitfield.is_a?(Bitfield)
      raise "bitfield lengths must be equal" if ! bitfield.length == length
        
      (@data.length).times do |i|
        @data[i] = @data[i] & bitfield.data[i]
      end
      self
    end
def intersection!(bitfield)
      raise "That's not a bitfield" if ! bitfield.is_a?(Bitfield)
      raise "bitfield lengths must be equal" if ! bitfield.length == length
        
      (@data.length).times do |i|
        @data[i] = @data[i] & bitfield.data[i]
      end
      self
    end
Update this bitfield to be the intersection of this bitfield and the passed bitfield.