问题
In C# I see that
-1 * int.MinValue == int.MinValue
Is this a bug? It really screwed me up when I was trying to implement a search tree. I ended up using (int.MinValue + 1) so that I could properly negate it.
回答1:
This is not a bug.
int.MinValue * -1 is 1 greater than int.MaxValue can hold. Thus, the number wraps around back to int.MinValue.
This is basically caused by an integer overflow.
Int32.MinValue:
The value of this constant is
-2,147,483,648
Int32.MaxValue:
The value of this constant is
2,147,483,647
So, -2,147,483,648 * -1 = 2,147,483,648 which is 1 greater than Int32.MaxValue.
回答2:
It's not a bug, it's an overflow.
In two's complement representation, the space of representable numbers is not symmetric. The opposite of the smallest integer cannot be represented. Computing it overflows and gives you the same number again.
回答3:
int i = -1 * int.MinValue;
This doesn't even compile unless you disable checking:
error CS0220: The operation overflows at compile time in checked mode
回答4:
No, it isn't a bug. It is the nature of twos complement integer arithmetic.
For example, let us take a signed byte value which goes between -128 and 127.
127(0x7f)+1 = 128(0x80). However, 0x80 is in fact the binary representation of -128.
Thus, for a byte, 128(0x80) = -128(0x80)
So -128(0x80) * -1 = 128(0x80) = -128(0x80)
回答5:
Put a checked region on it and see the "bug" evolve into an exception. Or try VB.NET (which as far as I recall is checked by default unlike C#).
来源：https://stackoverflow.com/questions/3622347/1-int-minvalue-int-minvalue-is-this-a-bug