compare time to calculate power function by 1) cmath pow, 2) log & exp and 3) direct multiplication.

time_power.cpp

#include <iostream> // for cin, cout
#include <cmath> // for log, exp, pow
#include <stdio.h>  // for printf
#include "timeit.h"

using namespace std; // std::cout ,...

float pow1(float base, float exponent){ // method 1 through direct multiplication
    float result=1;
    for(int i=1;i<=exponent;i++)result*=base;
    return result;
}

float pow2(float base, float exponent){ // method 2 through logarithmic multiplication
    float result=1;
    result=exp(exponent*log(base));
    return result;
}

float pow3(float base, float exponent){ // method 3 through builtin cmath algorighm
    float result=1;
    result=pow(base,exponent);
    return result;
}

int main(){
    float x=5.4;
    float y=20;
    int loops=1000000;
    float duration_us; // duration in microseconds
    float duration_us_prev;
    duration_us=timeit(x,y,pow1,loops);
    cout << "duration: " << duration_us << " microseconds/loop" << "\n";
    duration_us_prev=duration_us;
    duration_us=timeit(x,y,pow2,loops);
    cout << "duration: " << duration_us << " microseconds/loop" << "\n";
    if(duration_us<duration_us_prev)cout << "log";else cout << "direct";
    printf(" multiplication is %g%% faster \n",fmax(duration_us,duration_us_prev)/fmin(duration_us,duration_us_prev)*100-100);
    duration_us_prev=duration_us;
    duration_us=timeit(x,y,pow3,loops);
    cout << "duration: " << duration_us << " microseconds/loop" << "\n";
    if(duration_us<duration_us_prev)cout << "cmath";else cout << "log";
    printf(" multiplication is %g%% faster \n",fmax(duration_us,duration_us_prev)/fmin(duration_us,duration_us_prev)*100-100);
    return 0;
}

timeit.h

#include <chrono>

float timeit(float base, float exponent, float pow(float,float), int loops){
    float result;
    std::chrono::system_clock::time_point t1=std::chrono::high_resolution_clock::now();
    for(int i=1;i<=loops;i++)result=pow(base,exponent);
    std::chrono::system_clock::time_point t2=std::chrono::high_resolution_clock::now();
    printf("Test %g^%g=%0.10g, performed %d loops, ",base,exponent,result,loops);
    std::chrono::system_clock::duration time_diff=t2-t1;
    float duration_us=std::chrono::duration_cast<std::chrono::microseconds>(time_diff).count();
    return duration_us/loops;
}