2016 Update

Task/Four-bit-adder/Elixir/four-bit-adder.elixir

@@ -0,0 +1,47 @@
+defmodule RC do
+  use Bitwise
+  @bit_size 4
+
+  def four_bit_adder(a, b) do           # returns pair {sum, carry}
+    a_bits = binary_string_to_bits(a)
+    b_bits = binary_string_to_bits(b)
+    Enum.zip(a_bits, b_bits)
+    |> List.foldr({[], 0}, fn {a_bit, b_bit}, {acc, carry} ->
+         {s, c} = full_adder(a_bit, b_bit, carry)
+         {[s | acc], c}
+       end)
+  end
+
+  defp full_adder(a, b, c0) do
+    {s, c} = half_adder(c0, a)
+    {s, c1} = half_adder(s, b)
+    {s, bor(c, c1)}                     # returns pair {sum, carry}
+  end
+
+  defp half_adder(a, b) do
+    {bxor(a, b), band(a, b)}            # returns pair {sum, carry}
+  end
+
+  def int_to_binary_string(n) do
+    Integer.to_string(n,2) |> String.rjust(@bit_size, ?0)
+  end
+
+  defp binary_string_to_bits(s) do
+    String.codepoints(s) |> Enum.map(fn bit -> String.to_integer(bit) end)
+  end
+
+  def task do
+    IO.puts " A    B      A      B   C    S  sum"
+    Enum.each(0..15, fn a ->
+      bin_a = int_to_binary_string(a)
+      Enum.each(0..15, fn b ->
+        bin_b = int_to_binary_string(b)
+        {sum, carry} = four_bit_adder(bin_a, bin_b)
+        :io.format "~2w + ~2w = ~s + ~s = ~w ~s = ~2w~n",
+            [a, b, bin_a, bin_b, carry, Enum.join(sum), Integer.undigits([carry | sum], 2)]
+      end)
+    end)
+  end
+end
+
+RC.task