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一.补码加减运算
二.判断溢出方法
1.符号位判溢出方法
对于加减运算,两个异号数相加或者两个同号数相减,结果的绝对值一定比任何一个数的绝对值要小,不会发生上溢出。两个异号数相减或者两个同号数相加的绝对值肯定比任何一个数要大,可能发生溢出。
当两个符号相同的数补码相加时:
①结果符号位和操作数符号位相同:无溢出
②结果符号位和操作数相反:溢出
2.进位位判断溢出方法
两个符号位相同的数采用补码相加时,看结果的最高有效数值位和符号位。
①如果二者同时进位或者同时不进位,无溢出
②如果二者一个进位一个不进位则发生溢出
假设最高有效位进位Cn,符号位进位Cf,判断溢出标志位V,则有:
V=CnCf
3.双符号位判断溢出方法
双符号位顾名思义有两个符号位,且00为正,11为负
两个符号位相同的数补码相加时,若两符号位相同,则无溢出,两符号位不同则溢出.
且: 00正数 11负数
01正上溢 10负上溢