Question

已知机器字长8位,X=-61,Y=-79,试利用补码运算求X+Y的值,并判断是否发溢出

Answer 1

X = -61D = - 11 1101B

[X]原 = 1011 1101B

[X]反 = 1100 0010B

[X]补 = 1100 0011B

Y = -79D = -100 1111B

[Y]原 = 1100 1111B

[Y]反 = 1011 0000B

[Y]补 = 1011 0001B

求和：

[X]补 = 1100 0011B

[Y]补 = 1011 0001B (+

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[X+Y]补 = 10111 0100B

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↑（Cs是符号位的进位,Cp是最高数值位的进位,♁表示异或）

Cs♁Cp = 1♁0 = 1 ,负溢出

-[X+Y]反 =-0111 0011B

-[X+Y]原 =-1000 1100B

X+Y = -1000 1100B = -8CH = -140D