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Simple barrel shifter
Figure below shows the barrel shifter. In this case, the circuit shifts the input vector either 0 or 1 position to the left. When shift = 1, the LSB bit filled with '0' and when shift = 0, then outp = inp. When shift = 1, then outp(0) = '0' and outp(i) = inp(i - 1). The VHDL code of barrel shifter is shown bellow.
LIBRARY ieee;
USE ieee.std_logic_1164.all;
ENTITY barrel IS
GENERIC (n: INTEGER := 8);
PORT ( inp: IN STD_LOGIC_VECTOR (n-1 DOWNTO 0);
shift: IN INTEGER RANGE 0 TO 1;
outp: OUT STD_LOGIC_VECTOR (n-1 DOWNTO 0));
END barrel;
ARCHITECTURE RTL OF barrel IS
BEGIN
PROCESS (inp, shift)
BEGIN
IF (shift=0) THEN
outp <= inp;
ELSE
outp(0) <= '0';
FOR i IN 1 TO inp'HIGH LOOP
outp(i) <= inp(i-1);
END LOOP;
END IF;
END PROCESS;
END RTL;