--------------------------------------------------
-- 8-bit Barrel Shifter implemented as a
-- tree shifter with three stages
--
-- Alan R. Martello, University of Pittsburgh
--------------------------------------------------
entity BARREL is
port (data_in: in bit_vector(7 downto 0);
shift: in bit_vector(7 downto 0);
data_out: out bit_vector(7 downto 0)
);
end BARREL;
architecture logic of BARREL is
signal buffer_a, buffer_b: bit_vector(7 downto 0);
begin
--
-- stage one, shift one bit if needed
--
buffer_a(7 downto 0) <=
data_in(6 downto 0) & data_in(7) when shift(0)
else data_in(7 downto 0);
--
-- stage two, shift two bits if needed
--
buffer_b(7 downto 0) <=
buffer_a(5 downto 0) & buffer_a(7 downto 6)
when shift(1) else buffer_a(7 downto 0);
--
-- stage three, shift four bits if needed
--
data_out(7 downto 0) <=
buffer_b(3 downto 0) & buffer_b(7 downto 4)
when shift(2) else buffer_b(7 downto 0);
end logic;
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