C# - Unicode-Encoding ermitteln

using System;

public class EncodingHelper
{
    public static System.Text.Encoding DetectUnicodeEncoding(
	    System.IO.Stream s)
    {
	    if (s.CanSeek == false)
	        throw new InvalidOperationException();

    /*  EF BB BF 	UTF-8
        FF FE 	        UTF-16, little endian
        FE FF 	        UTF-16, big endian
        FF FE 00 00 	UTF-32, little endian
        00 00 FE FF 	UTF-32, big-endian */
        
        byte[] byteOrder = new byte[4];
        
        s.Read(byteOrder, 0, byteOrder.Length);
        
        s.Seek(0, System.IO.SeekOrigin.Begin);
        
        if ((byteOrder[0] == 0xEF) && (byteOrder[1] == 0xBB) && (byteOrder[2] == 0xBF))
            return System.Text.Encoding.UTF8;
        
        else if ((byteOrder[0] == 0xFF) && (byteOrder[1] == 0xFE))
            return System.Text.Encoding.Unicode;
        
        else if ((byteOrder[0] == 0xFE) && (byteOrder[1] == 0xFF))
            throw new NotSupportedException();
        
        else if ((byteOrder[0] == 0xFF) && (byteOrder[1] == 0xFE) && (byteOrder[2] == 0x0) && (byteOrder[3] == 0x0))
            return System.Text.Encoding.UTF32;
        
        else if ((byteOrder[0] == 0x0) && (byteOrder[1] == 0x0) && (byteOrder[2] == 0xFE) && (byteOrder[3] == 0xFF))
            throw new NotSupportedException(); 
            
        return null;
    }
}