对于负整数，返回零 [英] Return zero for negative integers

问题描述

一个朋友只是抛出了一些类似于以下C#代码的代码:

A friend just throw some code similar to following C# code:

int i = ...;
return i < 0 ? 0 : i;

这让我思考.有什么不同"的方法可以为负整数返回零，或者为当前正值返回零?更具体地说，如果可能的话，我正在寻找按位运算.

That made me think. There's any "different" way to return zero for negative integers, or current positive value? More specifically I'm looking for bitwise operations, if possible.

顺便说一句，我知道Math.Max(0, i);

推荐答案

Math.Max怎么了?

您可以使用按位操作执行等效操作而无需分支:

You can do the equivalent without a branch using bitwise operations:

r = x ^ ((x ^ y) & -(x < y)); // == max(x, y)

如果替换为零，它将折叠为:

If you substitute zero, it collapses to:

r = (y & -(0 < y)); // == max(0, y)

(来源:此列表按位技巧).

如果分支机构在您的平台上非常昂贵，那么我认为在某些内部循环中可能是值得的，但这是相当模糊的，不是我想在外部遇到的那种事情时间敏感功能.

If branches were extremely expensive on your platform, that might be worthwhile in some inner loop, I suppose, but it's pretty obscure and not the kind of thing I'd like to come across outside of an extremely time-sensitive function.

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