平方根元功能?

本文介绍了平方根元功能?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

是否可以使用具有以下签名的元函数来计算整数的平方根:

Is it possible to compute the square root of an integer with a metafunction with the following signature :

template<unsigned int N> inline double sqrt();

(或者也许使用constexpr关键字，我不知道什么是最好的). 这样，sqrt<2>()将在编译时替换为1.414....

(or maybe using the constexpr keyword, I don't know what is the best). With that, sqrt<2>() would be replaced by 1.414... at compile-time.

这种功能的最佳实现是什么?

What would be the best implementation for a such function ?

推荐答案

这可能不是您想要的，但我想确保您意识到，通常情况下，通过优化，编译器无论如何都会在编译时计算结果.例如，如果您具有以下代码:

This may not be what you are looking for, but I wanted to make sure you realized that typically with optimization the compiler will calculate the result at compile time anyway. For example, if you have this code:

void g() { f(sqrt(42)); }

对于具有优化-O2的g ++ 4.6.3，生成的汇编代码为:

With g++ 4.6.3 with optimization -O2, the resulting assembly code is:

9 0000 83EC1C subl $28, %esp 11 0003 DD050000 fldl .LC0 12 0009 DD1C24 fstpl (%esp) 13 000c E8FCFFFF call _Z1fd 14 0011 83C41C addl $28, %esp 16 0014 C3 ret 73 .LC0: 74 0000 6412264A .long 1244009060 75 0004 47EC1940 .long 1075440711

sqrt函数从不实际调用，其值仅存储为程序的一部分.

The sqrt function is never actually called, and the value is just stored as part of the program.

因此，要创建一个技术上满足您要求的功能，您只需要:

Therefore to create a function that technically meets your requirements, you simply would need:

template<unsigned int N> inline double meta_sqrt() { return sqrt(N); }