如果是五个模拟开关用VHDL语言编个优先编码器 1为最高级，然后一次 怎么写啊？谢谢啊！很急很急啊！

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
entity priority is
port(I : in bit_vector(4 downto 0);
A : out bit_vector(2 downto 0));
end priority;
architecture v1 of priority is
begin
process(I)
begin
if I(4) = '1' then--最高优先级
A <= "000";
elsif I(3) = '1' then--次优先级
A <= "001";
elsif I(2) = '1' then--
A <= "010";
elsif I(1) = '1' then
A <= "011";
elsif I(0) = '1' then
A <= "100";
else A<="111"
end if;
end process;
end v1;