// Initialize One’s Complement Fletcher Checksum
uns16 checksum = “initial value”;
...
// Loop through all data bytes, each stored at oneByte
// Update lower checksum byte
checksum.low8 += oneByte;
if ( Carry )
checksum.low8++;
// Update higher checksum byte
checksum.high8 += checksum.low8;
if ( Carry )
checksum.high8++;