XOR checksum of four bytes — parity and checksum

Why this example is worth doing

XORing all the bytes together gives a one-byte longitudinal redundancy check — cheap, and used in simple serial protocols. It is also weak in a specific and predictable way: it cannot detect reordering at all, because XOR is commutative, and it misses any error that flips the same bit position in two bytes. The page names those blind spots explicitly rather than presenting it as adequate.

Try your own input in the Parity & checksum. Even and odd parity, one’s-complement sums and the Internet checksum, step by step.