按位OR用于签名增强操作数 [英] Bitwise OR used for signature enhanced operand

问题描述

我有这个片段，.net编译器输出上面提到的警告。

Hi,
I have this snippet where the .net compiler outputs the above mentioned warning.

private static int BitwiseRotate(int x, int c)
{
	var num = (uint) x;
	return (int) (x << c | num >> 32 - c);
}

如果可能的话，我会更正此信息以获取警告。我不想放置任何编译器提示来省略此警告。



我想这个警告是因左右移位而来，但我不知道是否铸造会丢失数据。所以，如果有人有一些建设性意见，那就太棒了。



提前谢谢。

If possible I would correct this to get no warning. I do not want to place any compiler hint to ommit this warning.

I guess this warning comes because of the left- and right shifts, but I do not know if casting would loose data. So if anyone has some constructive advice it would be great.

Thanks in advance.

推荐答案

问题在于num和c的类型...

c是一个int（有符号），其中num是uint（unsigned）所以num>> 32-c将强制编译器将num扩展为int（unsigned）并且警告的原因...

The problem is with the types of num and c...
c is a int (signed) where num is uint (unsigned) so num >> 32- c will force the compiler to extend num to int (unsigned) and that the reason for the warning...

使用num变量有什么好处？ />


您的代码可缩短为：

What is the benefit of the use of the num variable?

Your code could be shortened to:

private static int BitwiseRotate(int x, int c) {
   return (x << c) | (x >> (32 - c));
}

无需在int和uint之间交叉演员。



我认为你首先遇到的问题是你忘记了一些括号：

No need to cross cast between int and uint.

I think the problem you had in the first place was that you forgot some parenthesis:

x >> 32 - c

应该是

should have been

x >> (32 - c)

因为右移运算符优先于减法运算;因此编译器理解

because the right-shift operator has precedence over subtraction; thus the compiler understood

(x >> 32) - c

它在逻辑上报告可能有问题。



希望这是有道理的。

which it logically reported as potentially problematic.

Hope this makes sense.

在C＃中，移位运算符不合逻辑，如果操作数为负数，则移位1.



private static int BitwiseRotate（int x，int c）// rotate left

{

var num =（uint）x;

return（int）（（num<< c）| num> ;>（32 - c））;

}

In C#, shift operators are not logical and if operand is negative, shifts 1.

private static int BitwiseRotate(int x, int c) // rotate left
{
var num = (uint) x;
return (int) ((num << c) | num >> (32 - c));
}

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