Use memcpy instead of strncpy when we know the length anyway. Modern gcc seems to think it knows how to detect misuse of strncpy, but it's wrong (in fact: very, very wrong) and the path of least resistance is to not try to fight with it.

grammar
  -> '0-9':d, !printf("%d\n", d);, '0-9':i = 10*d + 1;
  -> 'a-f':d, !printf("%d\n", d);, '0-9'