for $t from 1 to int(length(string) / 2):
  next unless the first $t chars equal the last $t;
  # i.e. "$t" must be a plausible tail-size.

  $r = length - $t;
  
  $incr = int($r / 2);
  while( $incr > 0) {
     next unless ($incr % $r == 0);
     # i.e. must be a possible repeated-block size in this space
     solution is found if string(0, $incr) eq string($incr, $incr);
     # i.e. if we find one repetition then it must be the answer.
     $incr--;
  }
}