blocks|key|1225229|text|计算机不会区分这一点。计算机不关心符号，你和编译器关心。您将把这个值存储到有符号变量中，然后将其作为有符号变量使用。长数和负数在语义上没有区别。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1225230|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Computer will not distinguish this. Computer doesn't care about sign, you and compiler do. You will store this value into signed variable and then use it as signed. There is no semantic difference between long numbers and negative numbers.

blocks|key|3326171|text|如果计算机使用的是2的补码，则不需要这样做。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3326172|让我们考虑一个更简单的例子，3-+5：|3326173|++++0011+=+3
-+++0101+=+5
————————
++++1110+=+14|code-block|syntax|javascript|3326174|结果是14，但在2的补码中，这也是-2的值。因此，如果代码使用带符号的类型，它将正确地得到-2。否则，它将得到14。这完全取决于程序员如何编写代码。|3326175|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

The computer doesn't need to, if it's using 2's complement.

Let's consider a simpler example, 3 - 5:

<pre><code> 0011 = 3
- 0101 = 5
————————
 1110 = 14
</code></pre>

The result is 14, but in 2's complement, this is also the value of -2. So, if the code uses signed type, it will correctly get -2. Otherwise, it will get 14. It all depends on how the programmer write the code.

blocks|key|1918239|text|计算机不做减法运算。它做了一个负数的加法。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1918240|因此，56+-66+=+56+%2B(-+66+)|1918241|56+=+0x38+(十六进制38+)|1918242|-66+=+0xFFFFFFBE+(32位系统中0x42的补码)|1918243|如果你将这些十六进制数字相加，你将得到0xFFFFFF6，这是一个十进制10的0xA的负数。|1918244|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|N|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|O|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|P|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|K|$]]

Computer does not do a subtraction. It does the addition of a negative number.

So, 56 - 66 = 56 + ( -66 )

56 = 0x38 ( 38 in hexadecimal )

-66 = 0xFFFFFFBE ( complement of 0x42 in a 32-bit system )

If you do would add these hex numbers you will end up with 0xFFFFFFF6, which is a negative complement of 0xA, which is a decimal 10.

blocks|key|3326293|text|通常，减法被实现为否定，然后是加法。因此，对于您的示例，CPU将在内部使用56和加法66。在x86+(或大多数其他现代处理器)上，求反将使用2的补码，这意味着求反转换为“对所有位进行补码，然后加1(并忽略任何进位)”。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3326294|++++0011+1000
-+++0100+0010
++++---------|code-block|syntax|javascript|3326295|第二个操作数的转换如下：|3326296|complement+bits:+1011+1101
Increment:+++++++1011+1110|3326297|所以执行的操作是：|3326298|++++0011+1000
%2B+++1011+1110
--------------
=+++1111+0110|3326299|可以将此结果视为246+(作为无符号数字)或-10+(作为有符号数字)。|3326300|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

Normally, subtraction is implemented as a negate, then add. So for your example, the CPU would internally take 56 and add -66. On an x86 (or most other modern processors) the negate will be done with two's complement, which means negate translates to "complement all the bits, then add one (and ignore any carry out)."

<pre><code> 0011 1000
- 0100 0010
 ---------
</code></pre>

The second operand is transformed as follows:

<pre><code>complement bits: 1011 1101
Increment: 1011 1110
</code></pre>

So the operation that's carried out is:

<pre><code> 0011 1000
+ 1011 1110
--------------
= 1111 0110
</code></pre>

This result can be viewed as either 246 (as an unsigned number) or -10 (as a signed number).

blocks|key|477111|text|进位标志与符号位不同。进位标志用于执行多部分运算，其中一个加法或减法的结果需要影响下一个更高的部分。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|477112|随着多年来寄存器大小的增加和assmbler的衰落，你不会再看到这样做了。|477113|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

The carry flag is not the same as a sign bit. The carry flag is used to do multi-part arithmetic, where the result of one addition or subtraction needs to affect the next higher part.

With the increase in register sizes over the years and the waning of assmbler, you don't see this done much anymore.

If a large number is subtracted from a smaller number then borrow is needed. The carry flag plays the role of borrow during the subtraction operation.
Now suppose we want to subtract 66 from 56, obviously the borrow is needed and carry flag will be set. Now how this subtraction is performed to get the result -10, how computer will distinguish that the result is going to be a negative number. Please explain the process.

carry flag and subtraction issue

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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如果从一个较小的数字中减去一个较大的数字，则需要借用。进位标志在减法操作期间起借位的作用。现在假设我们要从56中减去66，显然需要借位，并将设置进位标志。现在如何执行减法来获得结果-10，计算机如何区分结果将是负数。请解释一下流程。

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