在性能方面，按位运算符与标准模数有多快? [英] Performance wise, how fast are Bitwise Operators vs. Normal Modulus?

问题描述

在普通流或诸如for，if之类的条件语句中使用按位运算会提高整体性能，并且在可能的情况下使用它们会更好吗?例如:

Does using bitwise operations in normal flow or conditional statements like for, if, and so on increase overall performance and would it be better to use them where possible? For example:

if(i++ & 1) {

}

vs.

if(i % 2) {

}

推荐答案

除非您使用的是古老的编译器，否则它已经可以自行处理此级别的转换.也就是说，现代编译器可以并且将使用按位AND指令来实现i % 2，前提是可以在目标CPU上这样做(公平地说，通常会这样做).

Unless you're using an ancient compiler, it can already handle this level of conversion on its own. That is to say, a modern compiler can and will implement i % 2 using a bitwise AND instruction, provided it makes sense to do so on the target CPU (which, in fairness, it usually will).

换句话说，至少在使用具有合理能力的优化程序的现代编译器的情况下，不要期望它们之间在性能上有任何差异.在这种情况下，合理地"也有相当宽泛的定义-即使几十年前的相当多的编译器也可以毫不费力地处理这种微优化.

In other words, don't expect to see any difference in performance between these, at least with a reasonably modern compiler with a reasonably competent optimizer. In this case, "reasonably" has a pretty broad definition too--even quite a few compilers that are decades old can handle this sort of micro-optimization with no difficulty at all.

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