How do I Base58 Checked encode / decode an address in C#? What does "normalize leading zeros" mean?

I am trying to encode and decode a Base58 address in C#. The following function is a start, but it has a few issues:

• This code does not normalize leading zeros (what does that look like?)

• If this method is repeatedly called in rapid succession many string objects will be created, putting pressure on the GC

.NET 4.5 Code

Note add a reference to System.Numerics

BigInteger  bi =  System.Numerics.BigInteger.Parse("00010966776006953D5567439E5E39F86A0D273BEED61967F6", NumberStyles.HexNumber);string b58 = EncodeBase58(bi);Console.WriteLine(b58 + Environment.NewLine +"16UwLL9Risc3QfPqBUvKofHmBQ7wMtjvM");   /// .... SNIP   public static String sBase58Alphabet = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";    public static String EncodeBase58(BigInteger numberToShorten)    {        // WARNING: Beware of bignumber implementations that clip leading 0x00 bytes, or prepend extra 0x00         // bytes to indicate sign - your code must handle these cases properly or else you may generate valid-looking        // addresses which can be sent to, but cannot be spent from - which would lead to the permanent loss of coins.)        // Base58Check encoding is also used for encoding private keys in the Wallet Import Format. This is formed exactly        // the same as a Bitcoin address, except that 0x80 is used for the version/application byte, and the payload is 32 bytes        // instead of 20 (a private key in Bitcoin is a single 32-byte unsigned big-endian integer). Such encodings will always        // yield a 51-character string that starts with '5', or more specifically, either '5H', '5J', or '5K'.   https://en.bitcoin.it/wiki/Base58Check_encoding        const int sizeWalletImportFormat = 51;        char[] result = new char[33];        int i = 0;        while (numberToShorten >= 0 && result.Length > i)        {            var lNumberRemainder = BigInteger.Remainder(numberToShorten, (BigInteger)sBase58Alphabet.Length);            numberToShorten = numberToShorten / (BigInteger)sBase58Alphabet.Length;           result[result.Length - 1- i] = sBase58Alphabet[(int)lNumberRemainder] ;           i++;        }        return new string(result);    }    //public static long DecodeBase58(String base58StringToExpand)    //{    //    long lConverted = 0;    //    long lTemporaryNumberConverter = 1;    //    while (base58StringToExpand.Length > 0)    //    {    //        String sCurrentCharacter = base58StringToExpand.Substring(base58StringToExpand.Length - 1);    //        lConverted = lConverted + (lTemporaryNumberConverter * sBase58Alphabet.IndexOf(sCurrentCharacter));    //        lTemporaryNumberConverter = lTemporaryNumberConverter * sBase58Alphabet.Length;    //        base58StringToExpand = base58StringToExpand.Substring(0, base58StringToExpand.Length - 1);    //    }    //}