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--ACS_0.vhd  
--add-compare-select unit of viterbi 
--v0.1 
 
library ieee; 
use ieee.std_logic_1164.all; 
use ieee.std_logic_arith.all; 
 
entity ACS_0 is 
	port( 
		clk: in std_logic; 
		reset: in std_logic; 
		rc : in std_logic_vector(1 downto 0); 
		im_0: in std_logic_vector(5 downto 0); 
		im_2: in std_logic_vector(5 downto 0); 
		acs_0: out std_logic; 
		om_0: out std_logic_vector(5 downto 0) 
		); 
end ACS_0; 
 
architecture a of ACS_0 is 
 
begin 
	process(clk,reset) 
	variable mc_0: std_logic_vector(1 downto 0); 
	variable mc_2: std_logic_vector(1 downto 0); 
	variable up  : unsigned(5 downto 0); 
	variable low : unsigned(5 downto 0); 
	begin	 
		if rising_edge(clk) then 
			if reset='1' then 
				mc_0:="00"; 
				mc_2:="00"; 
				acs_0<='0'; 
				om_0<="000000"; 
			else 
			mc_0(0):=rc(0) xor rc(1);   
			mc_0(1):=rc(0) and rc(1);   
			mc_2(0):=(not rc(0)) xor (not rc(1)); 
			mc_2(1):=(not rc(0)) and (not rc(1)); 
			 
			up:=unsigned(im_0)+unsigned(mc_0); 
			low:=unsigned(im_2)+unsigned(mc_2); 
			 
				if up<=low then 
					acs_0<='0'; 
					om_0<=conv_std_logic_vector(up,6); 
				else 
					acs_0<='1'; 
					om_0<=conv_std_logic_vector(low,6); 
				end if;		 
			end if; 
		end if; 
	end process; 
end a;