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library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use ieee.math_real.all;
-------------------------------------------------------------------------------
entity barrel_shifter is
generic (
NBITS : positive := 8);
port (
din, d : in std_logic_vector(NBITS-1 downto 0); -- data in, shift distance
dout : out std_logic_vector(NBITS-1 downto 0)); -- data out
end entity barrel_shifter;
-------------------------------------------------------------------------------
architecture dfl of barrel_shifter is
-- TODO: Calculate the number of required shift stages as a constant.
constant nshift : natural := natural(log2(real(NBITS)));
-- custom vector for the shift stages
type my_vec is array(0 to nshift) of std_logic_vector(NBITS-1 downto 0);
signal vector : my_vec;
-- vector of zeros
constant ZEROS : std_logic_vector(NBITS-1 downto 0) := (others => '0');
begin -- architecture dfl
vector(0) <= din;
gen: for i in 0 to nshift-1 generate
vector(i+1) <= (vector(i)(NBITS-1-2**i downto 0)
& ZEROS(2**i-1 downto 0))
when d(i) = '1'
else vector(i);
end generate gen;
dout <= vector(nshift);
end architecture dfl;
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