说明：  对于带符号数的乘法运算，首先根据被乘数和乘数的符号位确定乘积的符号位，再进行无符号数乘法运算。如果积符为负，对积求补。
(Signed for the number of multiplication, first under the multiplicand and the multiplier sign bit to determine the product of the sign bit, and then carry out unsigned multiplication. If the plot symbol is negative, the right plot of Complement.)