-- 1 bit adder.

entity adder is
  port (i0, i1, ci : in bit; s, co : out bit);
end adder;

architecture rtl of adder is
begin
   s <= i0 xor i1 xor ci;
   co <= (i0 and i1) or (i0 and ci) or (i1 and ci);
end rtl;