问题描述

关于8086CPU标志寄存器溢出的问题

文章说，对于溢出只是针对于有符号数，但是对于无符号数，比如8为寄存器，表示的
范围是0~255，如果两个正数相加超过了255，不叫溢出了吗？为什么这里只讨论的是有
符号的数

解决方案

手头没有8086的文档，模糊记得eflags里面有CF和OF两个标记，你说的“溢出”应该对应CF，即产生了进位。OF对于有符号数。

The status flags (bits 0 2 4 6 7 and 11) of the EFLAGS register indicate the results of arithmetic instructions
such as the ADD SUB MUL and DIV instructions. The status flag functions are:
CF (bit 0) Carry flag — Set if an arithmetic operation generates a carry or a borrow out of the mostsignificant
bit of the result; cleared otherwise. This flag indicates an overflow condition for
unsigned-integer arithmetic.
OF (bit 11) Overflow flag — Set if the integer result is too large a positive number or too small a negative
number (excluding the sign-bit) to fit in the destination operand; cleared otherwise. This
flag indicates an overflow condition for signed-integer (two’s complement) arithmetic.