如何在C ++中展开短循环 [英] How to unroll a short loop in C++

问题描述

我想知道如何获得这样的东西:

I wonder how to get something like this:

1. 写

copy(a, b, 2, 3)

然后得到

And then get

a[2] = b[2];
a[3] = b[3];
a[4] = b[4];

我知道C #defines不能递归使用以获得这种效果.但是我使用的是C ++，所以我认为模板元编程可能是合适的.

I know that C #defines can't be used recursively to get that effect. But I'm using C++, so I suppose that template meta-programming might be appropriate.

我知道有一个 Boost 库，但我只想要这种简单"的技巧，而Boost太混乱".

I know there is a Boost library for that, but I only want that "simple" trick, and Boost is too "messy".

推荐答案

对此最简单的解决方案是编写一个循环，在该循环中，开始值和结束值是已知的:

The most straightforward solution to this is to write a loop where the start and end values are known:

for(int i = 2; i <= 4; i++) {
  a[i]=b[i]; 
}

我认为这比任何种类的模板/运行时调用混合物都更好:编写的循环对于编译器的优化器是完全清楚的，并且没有层次的函数调用可以深入了解正在发生的事情.

I think this is better than any sort of template/runtime-call mixture: The loop as written is completely clear to the compilers' optimizer, and there are no levels of function calls to dig through just to see what's going on.

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