怎么指定组合逻辑门的分布方式

LIBRARY IEEE;

USE IEEE.STD_LOGIC_1164.ALL;

USE IEEE.STD_LOGIC_UNSIGNED.ALL;

USE IEEE.STD_LOGIC_ARITH.ALL;



ENTITY com_8 IS

PORT

(

    datax : in std_logic_vector(7 downto 0);        --比较数据x

    datay : in std_logic_vector(7 downto 0);        --比较数据y

    c_out : out std_logic;                          --比较结果，x>y 输出1，否则输出0

    e_out : out std_logic;                          --比较结果，x=y 输出1，否则输出0

    c_in : in std_logic;                            --比较结果输入，用于级联 --大于

    e_in : in std_logic;                             --比较结构输入，用于级联 --相等

    --clk : in std_logic

);

END com_8;



ARCHITECTURE behavior OF com_8 IS



signal b_c, b_e : std_logic;

signal buff_e : std_logic_vector(7 downto 0);

signal equ : std_logic_vector(7 downto 0);



BEGIN



        process(clk)



        begin

                if(clk'event and clk='1') then

                        e_out <= b_e;

                        c_out <= b_c;

                end if;

        

        end process;

        

        buff_e(0) <= datax(0) xnor datay(0);

        buff_e(1) <= datax(1) xnor datay(1);

        buff_e(2) <= datax(2) xnor datay(2);

        buff_e(3) <= datax(3) xnor datay(3);

        buff_e(4) <= datax(4) xnor datay(4);

        buff_e(5) <= datax(5) xnor datay(5);

        buff_e(6) <= datax(6) xnor datay(6);

        buff_e(7) <= datax(7) xnor datay(7);

        

        

--        equ(0) <= (buff_e(7) and (datax(6) and(not datay(6))));

--        equ(1) <= (buff_e(7) and buff_e(6) and (datax(5) and(not datay(5))));

--        equ(2) <= (buff_e(7) and buff_e(6) and buff_e(5) and (datax(4) and(not datay(4))));

--        equ(3) <= (buff_e(7) and buff_e(6) and buff_e(5) and buff_e(4) and (datax(3) and(not datay(3))));

--        equ(4) <= (buff_e(7) and buff_e(6) and buff_e(5) and buff_e(4) and buff_e(3) and (datax(2) and(not datay(2))));

--        equ(5) <= (buff_e(7) and buff_e(6) and buff_e(5) and buff_e(4) and buff_e(3) and buff_e(2) and (datax(1)and(not datay(1))));

--        equ(6) <= (buff_e(7) and buff_e(6) and buff_e(5) and buff_e(4) and buff_e(3) and buff_e(2) and buff_e(1) and (datax(0)and(not datay(0))));

--        equ(7) <= (buff_e(7) and buff_e(6) and buff_e(5) and buff_e(4) and buff_e(3) and buff_e(2) and buff_e(1) and buff_e(0) and c_in);

        

        b_e <= buff_e(0) and buff_e(1) and buff_e(2) and buff_e(3) and buff_e(4) and buff_e(5) and buff_e(6) and buff_e(7) and e_in;

        

        --b_c <= (datax(7)and(not datay(7))) or equ(0) or equ(1) or equ(2) or equ(3) or equ(4) or equ(5) or equ(6) or equ(7);

        

        

        b_c <= (datax(7)and(not datay(7))) or 

                        (buff_e(7) and (datax(6) and(not datay(6)))) or 

                        (buff_e(7) and buff_e(6) and (datax(5) and(not datay(5)))) or 

                        (buff_e(7) and buff_e(6) and buff_e(5) and (datax(4) and(not datay(4)))) or

                        (buff_e(7) and buff_e(6) and buff_e(5) and buff_e(4) and (datax(3) and(not datay(3)))) or

                        (buff_e(7) and buff_e(6) and buff_e(5) and buff_e(4) and buff_e(3) and (datax(2) and(not datay(2)))) or

                        (buff_e(7) and buff_e(6) and buff_e(5) and buff_e(4) and buff_e(3) and buff_e(2) and (datax(1)and(not datay(1)))) or

                        (buff_e(7) and buff_e(6) and buff_e(5) and buff_e(4) and buff_e(3) and buff_e(2) and buff_e(1) and (datax(0)and(not datay(0)))) or

                        (buff_e(7) and buff_e(6) and buff_e(5) and buff_e(4) and buff_e(3) and buff_e(2) and buff_e(1) and buff_e(0) and c_in);



END behavior;