using System;

public class Program

{

    public static decimal Truncate(decimal d, byte decimals)

    {

        decimal r = Math.Round(d, decimals);

​

        if (d > 0 && r > d)

        {

            return r - new decimal(1, 0, 0, false, decimals);

        }

        else if (d < 0 && r < d)

        {

            return r + new decimal(1, 0, 0, false, decimals);

        }

        return r;

    }

    public static decimal Truncate2(decimal d, int decimals)

    {

        decimal step = (decimal)Math.Pow(10, decimals);

        decimal tmp = Math.Truncate(step * d);

        return tmp / step;      

    }

    public static void Assert(decimal expected, decimal value, byte precission)

    {

        var actual = Truncate(value, precission);

        var actual2 = Truncate2(value, precission);

        Console.WriteLine(String.Format("M1: {0}\t{1}\t{2}\t{3}", value, precission, actual, expected));

        Console.WriteLine(String.Format("M2: {0}\t{1}\t{2}\t{3}", value, precission, actual2, expected));

        Console.WriteLine();

    }

    public static void Main()

    {

        Assert(-1.12m, -1.129m, 2);

        Assert(-1.12m, -1.120m ,2);

        Assert(-1.12m, -1.125m ,2);

        Assert(-1.12m, -1.1255m,2);

        Assert(-1.12m, -1.1254m,2);

        Assert(0m,      0.0001m,3);

        Assert(0m,     -0.0001m,3);

        Assert(0m,     -0.0000m,3);

        Assert(0m,      0.0000m,3);

        Assert(1.1m,    1.12m  ,1);

        Assert(1.1m,    1.15m  ,1);

        Assert(1.1m,    1.19m  ,1);

        Assert(1.1m,    1.111m ,1);

        Assert(1.1m,    1.199m ,1);

        Assert(1.2m,    1.2m   ,1);

        Assert(0.1m,    0.14m  ,1);

        Assert(0,      -0.05m  ,1);

        Assert(0,      -0.049m ,1);

        Assert(0,      -0.051m ,1);

        Assert(-0.1m,  -0.14m  ,1);

        Assert(-0.1m,  -0.15m  ,1);

        Assert(-0.1m,  -0.16m  ,1);

        Assert(-0.1m,  -0.19m  ,1);

        Assert(-0.1m,  -0.199m ,1);

        Assert(-0.1m,  -0.101m ,1);

        Assert(0m,     -0.099m ,1);

        Assert(0m,     -0.001m ,1);

        Assert(1m,      1.99m  ,0);

        Assert(1m,      1.01m  ,0);

        Assert(-1m,    -1.99m  ,0);

        Assert(-1m,    -1.01m  ,0);     

    }

}