C# - Erkennen ob eine EXE (oder DLL) als 64bit kompiliert wurde

private bool CheckIsFile64bit(FileStream filestream)
{
    bool ret = false;

    Byte[] _data = new Byte[4];
    filestream.Seek(0x3c, SeekOrigin.Begin);
    filestream.Read(_data, 0, 4);
    int _offset = BitConverter.ToInt32(_data, 0);

    if (_offset > 0x3c)
    {
        _data = new Byte[4];
        filestream.Seek(_offset, SeekOrigin.Begin);
        filestream.Read(_data, 0, 4);

        if ((_data[0] == 0x50)
            && (_data[1] == 0x45)
            && (_data[2] == 0x00)
            && (_data[3] == 0x00))
        {

            // Read COFF File Header
            _data = new Byte[20];
            filestream.Read(_data, 0, 20);
            int _machine = BitConverter.ToInt16(_data, 0);
            //richTextBox_Output.Text += string.Format("Machine: 0x{0}" + System.Environment.NewLine, _machine.ToString("X4"));
            //int _numberOfSections = BitConverter.ToInt16(_data, 2);
            //richTextBox_Output.Text += string.Format("NumberOfSections: 0x{0}" + System.Environment.NewLine, _numberOfSections.ToString("X4"));
            //int _timeDateStamp = BitConverter.ToInt32(_data, 4);
            //double _secs = Convert.ToDouble(_timeDateStamp);
            //DateTime _dt = new DateTime(1970, 1, 1, 0, 0, 0).AddSeconds(_secs);
            //DateTime _tds = System.TimeZone.CurrentTimeZone.ToLocalTime(_dt);
            //richTextBox_Output.Text += string.Format("TimeDateStamp: {0} (0x{1})" + System.Environment.NewLine, _tds.ToString(), _timeDateStamp.ToString("X8"));
            //int _pointerToSymbolTable = BitConverter.ToInt32(_data, 8);
            //richTextBox_Output.Text += string.Format("PointerToSymbolTable: 0x{0}" + System.Environment.NewLine, _pointerToSymbolTable.ToString("X8"));
            //int _numberOfSymbols = BitConverter.ToInt32(_data, 12);
            //richTextBox_Output.Text += string.Format("NumberOfSymbols: 0x{0}" + System.Environment.NewLine, _numberOfSymbols.ToString("X4"));
            //int _sizeOfOptionalHeader = BitConverter.ToInt16(_data, 16);
            //richTextBox_Output.Text += string.Format("SizeOfOptionalHeader: 0x{0}" + System.Environment.NewLine, _sizeOfOptionalHeader.ToString("X4"));
            //int _characteristics = BitConverter.ToInt16(_data, 18);
            //richTextBox_Output.Text += string.Format("Characteristics: 0x{0}" + System.Environment.NewLine, _characteristics.ToString("X4"));

            // Read Optional Header
            _data = new Byte[2];
            filestream.Read(_data, 0, 2);
            int _magicNumber = BitConverter.ToInt16(_data, 0);
            //richTextBox_Output.Text += string.Format("Magic Number: 0x{0}" + System.Environment.NewLine, _magicNumber.ToString("X4"));
            if (_magicNumber == 0x010b)
                richTextBox_Output.Text += String.Format("File {0} is 32bit!" + System.Environment.NewLine, filestream.Name);
            else if (_magicNumber == 0x020b)
            {
                richTextBox_Output.Text += String.Format("File {0} is 64bit!" + System.Environment.NewLine, filestream.Name);
                ret = true;
            }
        }
        else
            richTextBox_Output.Text = "No PE File!";
    }
    else
        richTextBox_Output.Text = "Wrong Offset or no PE File!";

    return ret;
}