//  CRC32 function
//  To create a CRC from a new buffer, use this:
//      crc = MakeCRC32(mydata, data_len, 0);
//  If you need to continue the CRC (e.g. your data is in multiple buffers),
//  continue like this:
//      crc = MakeCRC32(moredata, more_len, crc);
//      
//  Your desired CRC should be the complement of the CRC generated by
//  MakeCRC32:
//      desired = crc
//      desired - crc = 0

unsigned long MakeCRC32(char *data, unsigned int len, unsigned long CRC);