规则
假定了A,B都是正数
加法:
整数: [A]补 + [B]补 = [A+B]补 (mod 2^(n+1))
小数: [A]补 + [B]补 = [A+B]补 (mod 2)
减法:
整数: [A-B]补 = [A]补 + [-B]补 (mod 2^(n+1))
小数: [A-B]补 = [A]补 + [-B]补(mod 2)
[-B]补的求法就是 [B]补的连同符号位在内,每位求反加一
例子
A = +15, B = +24,求[A-B]补
换成二进制原码:
A = +15 = 00001111;
B = +24 = 00011000
换成补码:(正数的原码补码相同)
[A]补 = 00001111,
[B]补 = 00011000,
[-B]补 = 11101000
[A-B]补 = [A]补 + [-B]补 = 00001111 +11101000 = 11110111