Counting the on bits in a bitfield using really bit integers as the data representation

counting_on_bits_in_a_bitfield.ex

# ...

  def has(bitfield) do
    count_elements(bitfield.pieces, 0)
  end

  defp count_elements(0, acc), do: acc
  defp count_elements(pieces, acc) do
    count_elements(pieces >>> 1, acc + (pieces &&& 1))
  end

# ...