求多项式的值，乘方函数

#include <iostream>
#include <time.h>
#include <random>
#include <iomanip>
using namespace std;

//求指数函数
inline double myPow(double x, int y)
{
    unsigned int n;

    //指数可能为负
    if (y >= 0)
    {
        n = y;
    } 
    else
    {
        n = -y;
    }

    //每次右移，相应x*=x，若当前最低位为1，则result *= x
    for (double result = 1; ; x *= x)
    {
        if ((n & 1) != 0)
        {
            result *= x;
        }
        if ((n >>= 1) == 0)
        {
            return (y >= 0)?result:1/result;//指数为负，取倒数
        }
    }
}
double polynomial(double a[], double x, int n)
{
    double re = 0;
    for (int i = 0; i < n; i++)
    {
        re += a[i] * myPow(x, i);
    }
    return re;
}
double polynomial_horner(double a[], double x, int n)
{
    double re = 0;
    for (int i = n - 1; i > 0; i--)
    {
        re = (a[i] + re) * x;
    }
    re += a[0];
    return re;
}
int main()
{
    mt19937 eng;
    eng.seed((unsigned)time(NULL));
    uniform_real<double> unif;
    const size_t size = 10000;
    double *a = new double[size];
    for (int i = 0; i < size; i++)
    {
        a[i] = unif(eng);
    }

    clock_t start = clock();
    cout << polynomial(a, 0.9, size) << endl;
    clock_t end = clock();
    double d = double(end - start)/CLOCKS_PER_SEC;
    cout << setprecision(4) << fixed << d << endl;

    start = clock();
    cout.unsetf(ostream::floatfield);
    cout << polynomial_horner(a, 0.9, size) << endl;
    end = clock();
    d = double(end - start)/CLOCKS_PER_SEC;
    cout << setprecision(4) << fixed << d;
}