用VHDL设计四个开关控制一盏灯的逻辑电路，要求改变任意开关的状态能够引起灯亮灭状态的改变。（即任一开

SIGNAL sw1, sw1_r : STD_LOGIC := '0';
SIGNAL sw2, sw2_r : STD_LOGIC := '0';
SIGNAL sw3, sw3_r : STD_LOGIC := '0';
SIGNAL sw4, sw4_r : STD_LOGIC := '0';
SIGNAL status : STD_LOGIC := '0';

sw_proc: PROCESS(clk)
BEGIN
IF RISING_EDGE(clk) THEN
IF rst = '1' THEN
sw1_r <= '0';
sw2_r <= '0';
sw3_r <= '0';
sw4_r <= '0';
status <= '0';
ELSE
IF (sw1_r /= sw1) OR
(sw2_r /= sw2) OR
(sw3_r /= sw3) OR
(sw4_r /= sw4) THEN
status <= NOT status;
END IF;
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sw1_r <= sw1;
sw2_r <= sw2;
sw3_r <= sw3;
sw4_r <= sw4;
END IF;
END IF;
END PROCESS;