什么情况下最好使用无条件AND（&而不是&&） [英] What are the cases in which it is better to use unconditional AND (& instead of &&)

问题描述

我想知道Java中的一些情况（或更一般地说：编程中的
）当布尔表达式中首选使用无条件 AND 时（& ）而不是条件版本（&& ）。

I'd like to know some cases in Java (or more generally: in programming) when it is preferred in boolean expressions to use the unconditional AND (&) instead of the conditional version (&&).

我知道它们是如何工作的，但我不能考虑使用单个& 值得的情况。

I know how they work, but I cannot think about a case when use the single & is worth it.

推荐答案

我在现实生活中找到了表达式两边都非常便宜的案例，所以它削减了一两纳秒以避免分支和使用无条件& 而不是&& 。 （但这些是非常高性能的数学实用程序;我几乎从不在其他代码中使用它，如果没有详尽的基准测试来证明它更好，我也不会这样做。）

I have found cases in real life where both sides of the expression were really cheap, so it shaved off a nanosecond or two to avoid the branch and to use the unconditional & instead of &&. (These were extremely high-performance math utilities, though; I would almost never use this in other code, and I wouldn't have done it anyway without exhaustive benchmarking to prove it was better.)

（举个具体的例子， x> 0 将是超级廉价和无副作用。为什么要冒险分支错误预测以避免一个测试会变得如此便宜吗？当然，因为它是一个 boolean 最终结果将在分支中使用，但如果（x> = 0&& x< = 10）涉及两个分支， if（x> = 0& x< = 10）只涉及一个。）

(To give specific examples, x > 0 is going to be super cheap and side-effect-free. Why bother risking a branch misprediction to avoid a test that's going to be so cheap anyway? Sure, since it's a boolean the end result is going to be used in a branch anyway, but if (x >= 0 && x <= 10) involves two branches, and if (x >= 0 & x <= 10) involves only one.)

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