entity SHIFTER is
  generic(DEL: TIME);
  port(DATA_IN: in BIT_VECTOR(3 downto 0);
       SR,SL: in BIT; IL,IR: in BIT;
       DATA_OUT: out BIT_VECTOR(3 downto 0));
end SHIFTER;

architecture  ALG of SHIFTER is
begin
  process(SR,SL,DATA_IN,IL,IR)
    variable CON: BIT_VECTOR(0 to 1);
  begin
    CON := SR&SL;
    case CON is
      when "00" => DATA_OUT <= DATA_IN after DEL;
      when "01" => DATA_OUT <= DATA_IN(2 downto 0) & IL
                   after DEL;
      when "10" => DATA_OUT <= IR & DATA_IN(3 downto 1)
                   after DEL;
      when "11" => DATA_OUT <= DATA_IN after DEL;
    end case;
  end process;
end ALG;
--Figure 4.25 Shifter primitive.