问制作用VHDL语言显示月数和月日的日历？

EN

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

entity Days_In_Month is
   port (
      I_MONTH         : in  unsigned(3 downto 0);
      I_LEAP_YEAR     : in  std_logic;
      O_DAYS_IN_MONTH : out unsigned(4 downto 0)
      );
end entity Days_In_Month;

architecture Days_In_Month_combinatorial of Days_In_Month is

   signal month_30d : std_logic;
   signal month_28d : std_logic;
   signal month_31d : std_logic;
   signal month_29d : std_logic;

begin

   month_30d <= '1' when I_MONTH = 9 or
                         I_MONTH = 4 or
                         I_MONTH = 6 or
                         I_MONTH = 11
                    else '0';

   month_28d <= '1' when I_MONTH = 2 and
                         I_LEAP_YEAR = '0'
                    else '0';
   month_29d <= '1' when I_MONTH = 2 and
                         I_LEAP_YEAR = '1'
                    else '0';
   month_31d <= '1' when month_30d = '0' and
                         month_28d = '0' and
                         month_29d = '0'
                    else '0';

   O_DAYS_IN_MONTH <= to_unsigned(30,O_DAYS_IN_MONTH'length) when month_30d = '1' else
                      to_unsigned(28,O_DAYS_IN_MONTH'length) when month_28d = '1' else
                      to_unsigned(29,O_DAYS_IN_MONTH'length) when month_29d = '1' else
                      to_unsigned(31,O_DAYS_IN_MONTH'length) when month_31d = '1'
                      else to_unsigned(0,O_DAYS_IN_MONTH'length);                   

end architecture Days_In_Month_combinatorial;