汇编-进位标志VS溢出标志
我有下一个代码：
mov al, -5
add al, 132
add al, 1
当我检查它时，溢出标志和进位标志将在第一个操作中设置，而在第二个操作中，仅设置溢出。
但我不明白为什么：
- 在无符号数中，结果是143（8FH），因此适合8位无符号数（小于255）=>不应设置进位标志。在有符号数中，结果为127，适合8位有符号，不应设置溢出。
怎么了？谢谢。
I have the next code:
mov al, -5
add al, 132
add al, 1
As I check it, the overflow flag and the carry flag will set in the first operation, and in the second, only the overflow will set.
But I don't understand why:
- In unsigned number, the result is 143 (8FH), and for that is fit 8-bit unsigned number (is smaller than 255) => the carry flag shouldn't be set. In signed number, the result is 127, It's fit to 8-bit signed, and the overflow shouldn't be set.
Whats wrong? Thanks.
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当两个正数相加的结果为负数或
两个负数相加的结果是正数。
例如：
+127+1=?当我们查看两个操作数的符号位和
结果发现发生了溢出，答案不正确。
Overflow occurs when the result of adding two positive numbers is negative or
the result of adding two negative numbers is positive.
For instance:
+127+1=?As we look at the sign bits of the two operands and the sign bit of
the result, we find out that Overflow occurred and the answer is incorrect.
在无符号算术中，您将
0xFB添加到0x84，即251 + 132，它确实大于8位，因此设置了进位标志。在第二种情况下，您将+127 加到1，这确实超出了有符号的8 位范围，因此设置了溢出标志。
In unsigned arithmetic, you have added
0xFBto0x84, i.e. 251 + 132, which indeed is larger than 8-bit, and so the carry flag is set.In the second case, you are adding +127 to 1, which indeed exceeds a signed 8-bit range, and so the overflow flag is set.