Subversion Repositories xucpu

LIBRARY IEEE;

USE IEEE.STD_LOGIC_1164.ALL;

USE IEEE.NUMERIC_STD.ALL;

ENTITY shift IS

  GENERIC (

    w_data : NATURAL RANGE 1 TO 32 := 16);

  PORT (

    A  : IN  STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0);

    OP : IN  STD_LOGIC_VECTOR(1 DOWNTO 0);

    Y  : OUT STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0));

END shift;

ARCHITECTURE Behavioral OF shift IS

  CONSTANT ZERO : STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0)

    := (OTHERS => '0');

  CONSTANT ONE  : STD_LOGIC_VECTOR(w_data - 1 DOWNTO 0)

    := STD_LOGIC_VECTOR(to_unsigned(1, w_data));

BEGIN  -- Behavioral

  SH1: PROCESS (A,OP)

  BEGIN  -- PROCESS SH1

    CASE OP IS

      WHEN "00" =>

        Y <= A(14 DOWNTO 0) & '0';

      WHEN "01" =>

        Y <= '0' & A(15 DOWNTO 1);

      WHEN "10" =>

        Y <= ZERO;

      WHEN "11" =>

        Y <= ONE;

      WHEN OTHERS =>

        NULL;

    END CASE;

  END PROCESS SH1;

END Behavioral;