Double sign bit method1. The number participating in the addition and subtraction operation is represented by the deformed complement (the two sign bits of the positive number are "00", the two sign bits of the negative number are "11", and the mantissa rule is the same as the complement)2. Participate in operation together with symbol bit3. Judge whether the result overflows according to two symbol bitsSingle sign bit method1. Participate in operation together with symbol bit2. Find the carry cfcf generated by the sign bit and the carry c0c0 generated by the most significant bit respectively3. Judge whether the result overflows according to CFC and c0c0