pack_fun.vhd

来自「VHDL子程序集,包括各种例程资料以及源码.」· VHDL 代码 · 共 53 行

--****************************************
--*     PACKAGE FUNCTION DECLARATION     *
--****************************************

library IEEE;
use IEEE.std_logic_1164.all;

PACKAGE PACK_FUN is

function MUL4 (
               I: std_logic_vector (0 to 3);
	       S: std_logic_vector (1 downto 0)
	      ) return std_logic;
function MUL2 (
               I: std_logic_vector (0 to 1);
               S: std_logic
	      ) return std_logic;
end PACK_FUN;

PACKAGE BODY PACK_FUN IS

function MUL4 (
               I: std_logic_vector (0 to 3);
	       S: std_logic_vector (1 downto 0)
	      ) return std_logic is 
         variable F: std_logic;
begin
    case S is
         when "00"   => F := I(0);
         when "01"   => F := I(1);
	 when "11"   => F := I(3);
         when others => null;
    end case;
    return F;   
end MUL4;

function MUL2 (
               I: std_logic_vector (0 to 1);
               S: std_logic
	      ) return std_logic is
         variable F: std_logic;
begin 
    case S is
         when '0'    => F := I(0);
         when '1'    => F := I(1);
         when others => null;
    end case;
    return F;   
end MUL2;

end PACK_FUN;