public void UpdateChecksum()
{
// calculate the checksum in the file
FileInfo fi = new FileInfo(m_fileName);
byte[] fileContent = readbytesFromFile(m_fileName, 4, (int)(fi.Length - 4));
Int32 calcChecksum = 0;
foreach (byte b in fileContent)
{
calcChecksum += Convert.ToInt32(b);
}
writeInt32ToFile(m_fileName, 0, calcChecksum);
}