using System;

using System.Diagnostics;

using System.Numerics;

using System.Threading.Tasks;

using System.Threading; // For ThreadLocal<T>

​

class Program

{

    static void Main(string[] args)

    {

        Console.Write("Enter the number of decimal places to calculate Pi: ");

        if (int.TryParse(Console.ReadLine(), out int decimalPlaces))

        {

            if (decimalPlaces < 0)

            {

                Console.WriteLine("Please enter a non-negative number.");

                return;

            }

​

            Stopwatch stopwatch = new Stopwatch();

            stopwatch.Start();

​

            string pi = CalculatePi(decimalPlaces);

​

            stopwatch.Stop();

            Console.WriteLine($"Pi to {decimalPlaces} decimal places: {pi}");

            Console.WriteLine($"Time taken: {stopwatch.ElapsedMilliseconds} ms");

        }

        else

        {

            Console.WriteLine("Invalid input. Please enter a valid number.");

        }

    }

​

    static string CalculatePi(int decimalPlaces)

    {

        // Use ThreadLocal to store intermediate results for each thread

        // Set trackAllValues to true to allow access to the Values property

        ThreadLocal<BigInteger> localPi = new ThreadLocal<BigInteger>(() => 0, trackAllValues: true);

​

        BigInteger sixteen = 16;

        BigInteger one = 1;

​

        // Parallel calculation using all CPU cores

        Parallel.For(0, decimalPlaces, i =>

        {

            BigInteger term1 = 4 / (8 * (BigInteger)i + 1);

            BigInteger term2 = 2 / (8 * (BigInteger)i + 4);

            BigInteger term3 = 1 / (8 * (BigInteger)i + 5);

            BigInteger term4 = 1 / (8 * (BigInteger)i + 6);

​

            BigInteger term = term1 - term2 - term3 - term4;

            term *= BigInteger.Pow(sixteen, decimalPlaces - 1 - i);

​

            // Add the term to the thread-local result

            localPi.Value += term;

        });

​

        // Combine results from all threads

        BigInteger pi = 0;

        foreach (var threadResult in localPi.Values)

        {

            pi += threadResult;

        }

​

        string piString = pi.ToString();

        return piString.Insert(1, "."); // Insert the decimal point

    }

}