MOV AH,F(xiàn)FH MOV BL,[B] SUB AH,BL MOV BH,[A] SUB BH,AH MOV [C],BH
MOV DX,7FH SUB AX,DX MOV DX,0FFH SUB DX,BX MOV BX,DX
MOV BL,0FH AND BL,AL SAL 4 SHR 4 XOR AL,BL