如何测试两种算法并确定哪种算法更快?

使用来自的时钟 this answer

#include <iostream>
#include <chrono>

class Timer
{
public:
    Timer() : beg_(clock_::now()) {}
    void reset() { beg_ = clock_::now(); }
    double elapsed() const { 
        return std::chrono::duration_cast<second_>
            (clock_::now() - beg_).count(); }

private:
    typedef std::chrono::high_resolution_clock clock_;
    typedef std::chrono::duration<double, std::ratio<1> > second_;
    std::chrono::time_point<clock_> beg_;
};

您可以编写一个程序来计时这两个函数。

int main() {
    const int N = 10000;
    Timer tmr;

    tmr.reset();
    for (int i = 0; i < N; i++) {
        auto value = fiborecursion(i%50);
    }
    double time1 = tmr.elapsed();

    tmr.reset();
    for (int i = 0; i < N; i++) {
        auto value = fiboconstant(i%50);
    }
    double time2 = tmr.elapsed();

    std::cout << "Recursion"
            << "\n\tTotal: " << time1
            << "\n\tAvg: " << time1 / N
            << "\n"
            << "\nConstant"
            << "\n\tTotal: " << time2
            << "\n\tAvg: " << time2 / N
            << "\n";
}

我会尝试在没有编译器优化的情况下编译( -O0 )和max编译器优化( -O3 )看看有什么不同。在最大优化时,编译器可能会完全消除循环。