Base36 Encoding

Base36.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace Minimize.Models.Utils
{
    public class Base36
    {
        private const string Base36CharSet = "0123456789abcdefghijklmnopqrstuvwxyz";

        public static string Encode(ulong raw)
        {
            char[] base36Chars = Base36CharSet.ToCharArray();
            var result = new Stack<char>();
            while (raw != 0)
            {
                result.Push(base36Chars[raw % 36]);
                raw /= 36;
            }
            return new string(result.ToArray());
        }

        public static ulong Decode(string encoded)
        {
            ulong decoded = 0;

            uint pos = 0;
            foreach (var charSetIdx in encoded.ToLower().Reverse().Select(c => Base36CharSet.IndexOf(c)))
            {
                if (charSetIdx < 0)
                {
                    throw new ArgumentOutOfRangeException("encoded", encoded, "Value to decode must be in base 36 (i.e. only contain characters \"" + Base36CharSet + "\".");
                }

                decoded += (ulong)(charSetIdx * (int)Math.Pow(36, pos++));
            }

            return decoded;
        }
    }
}