And think of the classic code for copying a NUL-terminated string. Unless I'm missing some clever optimization, replacing it with a length-based version would

And think of the classic code for copying a NUL-terminated string. Unless I'm missing some clever optimization, replacing it with a length-based version would require another counter variable -- meaning the algorithm would use another register (or even possibly two on an 8-bit machine) and require another operation for each character. Not such a big deal now, but it would have been a big advantage for NUL-termination back in when C was designed.