using System;

using System.Diagnostics; 

public class Program

{

    public static int ModuloBitShiftRussianPeasant(int i, int j)

    {

        if (i <= j) //trivial modulo

            return (i == j) ? 0 : i;

        else if (j==0)

            return i;

​

        int x = j;

        int halfi = i >> 1;

        while (x < halfi)

        {

            x <<= 1;

        }

        while (i >= j)

        {

            if (i >= x)

                i -= x;

            else

                x >>= 1;

        }

        return i;

    }

    public static int ModuloDecimalMath(int i, int j)

    {

        if (i <= j) //trivial modulo

            return (i == j) ? 0 : i;

        else if (j==0)

            return i;

        decimal decresult = i/(decimal)j; 

        //Console.WriteLine("decresult="+decresult.ToString());

        //Console.WriteLine("denominator="+(decresult - (int)decresult ).ToString()); 

        //Console.WriteLine("modulo="+((decresult - (int)decresult)*j).ToString()); 

        //modulo=3.999999999999999999999999997 issue! 

        //decimal modulo = (decresult - (int)decresult)*j;      

        return (int)(((decresult - (int)decresult)*j)+0.000000000000000000000000003M); //add correction

    }

    public static int ModuloMathString(int i, int j)

    {

        if (i <= j) //trivial modulo

            return (i == j) ? 0 : i;

        else if (j==0)

            return i;

        string decresult = (i/(decimal)j).ToString();

        int idxperiod = decresult.IndexOf('.'); 

        if (idxperiod > -1 )

        {

            string denominator = decresult.Substring(idxperiod); 

            //Console.WriteLine("denominator="+Convert.ToDecimal(denominator).ToString());       

            i = (int)(j*(Convert.ToDecimal(denominator)+0.000000000000000000000000003M)); 

        }

        else 

            i = Convert.ToInt32(decresult); 

        return i;

    }

    public static int ModuloMathAdditive(int i, int j)

    {

        if (i <= j) //trivial modulo

            return (i == j) ? 0 : i;

        else if (j==0)

            return i;

       int total = 0;

       int y = 0;

        for (int x = 0; x < i; x++)

        {

            //Console.WriteLine("y {0} > {1} ",y,  (j - 1));

            if (y > (j - 1))

            {

                total += y;

                y = 0;

                //Console.WriteLine("x={0} total={1}",y, total);

            }

            y += 1;

            if ((total + y) >= i) return y;  

        }

        return total;

    }

    public static void Main()

    {

        int number = 123; 

        int div = 7; 

        int mod = 0; 

        Stopwatch sw = new Stopwatch(); 

        sw.Start(); 

        mod = number % div; 

        sw.Stop();

        Console.WriteLine("{0} % {1} mod={2}",number,div,mod);

        Console.WriteLine(sw.ElapsedTicks+" ticks");

        sw.Reset();

        sw.Start(); 

        mod = ModuloBitShiftRussianPeasant(number, div); 

        sw.Stop();

        Console.WriteLine("ModuloBitShiftRussianPeasant mod="+mod);

        Console.WriteLine(sw.ElapsedTicks+" ticks");

        sw.Reset();

        sw.Start(); 

        mod = ModuloDecimalMath(number, div); 

        sw.Stop();

        Console.WriteLine("ModuloDecimalMath mod="+mod);

        Console.WriteLine(sw.ElapsedTicks+" ticks");

        sw.Reset();

        sw.Start(); 

        mod = ModuloMathString(number, div); 

        sw.Stop();

        Console.WriteLine("ModuloMathString mod="+mod);

        Console.WriteLine(sw.ElapsedTicks+" ticks");

        sw.Reset();

        sw.Start(); 

        mod = ModuloMathAdditive(number, div); 

        sw.Stop();

        Console.WriteLine("ModuloMathAddative mod="+mod);

        Console.WriteLine(sw.ElapsedTicks+" ticks");

    }

}