在Java中，以下哪段代码更快？ [英] Which of these pieces of code is faster in Java

问题描述

我想知道哪段代码会运行得更快，因为我想尽可能地优化。

I was wondering which piece of code is going to run faster since I want to optimize as much as possible.

代码A：

if(((a & 0x0FFF) + (b & 0x0FFF)) & 0x1000 != 0)
{
    Register.setHCarryFlag(true);
}
else
{
    Register.setHCarryFlag(false);
}

代码B：

Register.setHCarryFlag(((a & 0x0FFF) + (b & 0x0FFF))& 0x1000 != 0);

我问的原因是我怀疑代码B没有分支，但我不知道确保将它们分别转换为机器代码。

The reason I ask is I suspect that code B doesn't branch, but I don't know for sure how each is converted to machine code.

更好的是，有没有办法查看每段代码生成的机器代码？

Better yet, is there a way to see the machine code that is produced from each piece of code?

推荐答案

无论如何，使用第二种方法都将更加安全，因为从根本上讲，这里没有分支，只有纯粹的计算。一个好的JIT编译器可能会认识到可以消除您在第一个示例中的分支，但是为什么对JIT和人类读者来说却变得更加困难。

However you turn it, you'll be safer with the second approach because there is fundamentally no branching there, just pure calculation. A good JIT compiler may recognize that your branch in the first example can be eliminated, but why make it more difficult for JIT—and for a human reader.

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