struct UpdateFileHeader
{
   UINT16 HdrSize; // always 0x0018
   BYTE override; // 0x01 => override with new file; 0x04 => update file (bsdiff)
   BYTE version; // always 0x04
   UINT32 unknown3;
   UINT32 OldFileSize; // file size before the update (uncompressed)
   UINT32 NewFileSize; // size of the entire file after the update is applied (uncompressed)
   UINT32 unknown6; // always 0
   UINT32 unknown7; // always 0
};