hamming_12_8.vhd

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity hamming_12_8 is
    Port ( 
           data_in : in  STD_LOGIC_VECTOR(7 downto 0);
           parity_out : out  STD_LOGIC_VECTOR(3 downto 0);
           msb_parity_out : out std_logic);
end hamming_12_8;

architecture Behavioral of hamming_12_8 is
    signal parity_out_s : std_logic_vector(3 downto 0);
begin
    process(data_in, parity_out_s)
    begin
        -- calculate the parity bits
        parity_out_s(0) <= data_in(0) xor data_in(1) xor data_in(3) xor data_in(4) xor data_in(6);
        parity_out_s(1) <= data_in(0) xor data_in(2) xor data_in(3) xor data_in(5) xor data_in(6);
        parity_out_s(2) <= data_in(1) xor data_in(2) xor data_in(3) xor data_in(7);
        parity_out_s(3) <= data_in(4) xor data_in(5) xor data_in(6) xor data_in(7);

        msb_parity_out <= (((data_in(0) xor data_in(1)) xor (data_in(2) xor data_in(3))) xor 
                          ((data_in(4) xor data_in(5)) xor (data_in(6) xor data_in(7)))) xor 
                          ((parity_out_s(0) xor parity_out_s(1)) xor (parity_out_s(2) xor parity_out_s(3)));

        parity_out <= parity_out_s;
    end process;
end Behavioral;