def copyFrom(bitfield)
      raise "Source bitfield is too small (#{bitfield.length} < #{length})" if bitfield.length < length
      (@data.length).times do |i|
        @data[i] = bitfield.data[i]
      end
    end
def copyFrom(bitfield)
      raise "Source bitfield is too small (#{bitfield.length} < #{length})" if bitfield.length < length
      (@data.length).times do |i|
        @data[i] = bitfield.data[i]
      end
    end
Set the contents of this bitfield to be the same as the passed bitfield. An exception is
 thrown if the passed bitfield is smaller than this.