#include <iostream>
#include <iomanip>
#include <cmath>
 
// fast pow for int, credit to https://stackoverflow.com/a/101613/13188071
int ipow(int base, int exp)
{
    int result = 1;
    while (true)
    {
        if (exp & 1)
            result *= base;
        exp >>= 1;
        if (exp == 0)
            break;
        base *= base;
    }
 
    return result;
}
 
double round_prec(double n, int prec)
{
    return std::round(n * ipow(10, prec)) / ipow(10, prec);
}
 
int main()
{
    std::cout << std::setprecision(20) << round_prec(3.1415, 2) << '\n';
}

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