library ieee;
use ieee.std_logic_1164.all;

entity hamm_dec_4b is
        port
                (
                        code : in std_logic_vector(6 downto 0);
                        data : out std_logic_vector(3 downto 0);
                        status : out std_logic
                );
end hamm_dec_4b;

architecture Behavioural of hamm_dec_4b is
signal syndrom_nez : std_logic;
signal syndrom : std_logic_vector(2 downto 0);
begin
----------------------------------------------------------------------
-- HAMMING DECODER (7,4)
----------------------------------------------------------------------
  -- SYNDROM ------------------------------------------------------------------
  syndrom(0) <=     code( 0) xor code( 2) xor code( 4) xor code( 6)
                ;
  syndrom(1) <=     code( 1) xor code( 2) xor code( 5) xor code( 6)
                ;
  syndrom(2) <=     code( 3) xor code( 4) xor code( 5) xor code( 6)
                ;

  syndrom_nez <= syndrom(0) or syndrom(1) or syndrom(2) ;

  -- CORRECTED DATA -----------------------------------------------------------
  data( 0) <= code( 2) xor
                (syndrom(0) and syndrom(1) and (not syndrom(2)) );
  data( 1) <= code( 4) xor
                (syndrom(0) and (not syndrom(1)) and syndrom(2) );
  data( 2) <= code( 5) xor
                ((not syndrom(0)) and syndrom(1) and syndrom(2) );
  data( 3) <= code( 6) xor
                (syndrom(0) and syndrom(1) and syndrom(2) );

  -- STATUS -------------------------------------------------------------------
  status <= syndrom_nez;    -- "0" : everything ok
                            -- "1" : data corrected
end Behavioural;