/*
VIM: let b:cf5build="clang -std=c++20 -O2 -pthread -lstdc++ -I. {SRC} -o {OUT}"
VIM: let b:cf5run="{OUT}"
*/
#include <iostream>
#include <exception>
#include <chrono>

/* This is from "The C++ Programming Language, Fourth Edition 
 * by Bjarne Stroustrup"*/
constexpr int sqrt2(int x, int i = 3, int i_sq = 1){
    return i_sq <= x ? sqrt2(x, i+2, i_sq + i) : i/2-1;
}

/* My simplified version:
 * Basically sum(1+2*i) where i==0..n-1 == n^2
 */
constexpr int sqrt(int x, int i = 1, int i_sq = 1){
    return i_sq <= x ? sqrt(x, i+1, i_sq + (1+2*i)) : i-1;
}


int main ( void )
{try{
    auto begin = std::chrono::high_resolution_clock::now();

    std::cout << "sqrt(-1)=" << sqrt(-1) << " vs " << sqrt2(-1) << std::endl;
    std::cout << "sqrt(0)=" << sqrt(0) << " vs " << sqrt2(0) << std::endl;
    std::cout << "sqrt(1)=" << sqrt(1) << " vs " << sqrt2(1) << std::endl;
    std::cout << "sqrt(2)=" << sqrt(2) << " vs " << sqrt2(2) << std::endl;
    std::cout << "sqrt(3)=" << sqrt(3) << " vs " << sqrt2(3) << std::endl;
    std::cout << "sqrt(4)=" << sqrt(4) << " vs " << sqrt2(4) << std::endl;
    std::cout << "sqrt(5)=" << sqrt(5) << " vs " << sqrt2(5) << std::endl;
    std::cout << "sqrt(6)=" << sqrt(6) << " vs " << sqrt2(6) << std::endl;
    std::cout << "sqrt(9)=" << sqrt(9) << " vs " << sqrt2(9) << std::endl;
    std::cout << "sqrt(16)=" << sqrt(16) << " vs " << sqrt2(16) << std::endl;
    std::cout << "sqrt(24)=" << sqrt(24) << " vs " << sqrt2(24) << std::endl;
    std::cout << "sqrt(25)=" << sqrt(25) << " vs " << sqrt2(25) << std::endl;
    std::cout << "sqrt(26)=" << sqrt(26) << " vs " << sqrt2(26) << std::endl;
    std::cout << "sqrt(36)=" << sqrt(36) << " vs " << sqrt2(36) << std::endl;

    //......

    auto end = std::chrono::high_resolution_clock::now();
    std::chrono::duration<double> seconds = end - begin;
    std::cout << "Time: " << seconds.count() << std::endl;
    return 0;
}
catch ( const std::exception& e )
{
    std::cerr << std::endl
            << "std::exception(\"" << e.what() << "\")." << std::endl;
    return 2;
}
catch ( ... )
{
    std::cerr  << std::endl
            << "unknown exception." << std::endl;
    return 1;
}}