for (0..($strLen - 1))
  {
  $copy .= substr $copy, 0, 1, '';
  $cycleLen = $_ + 1;
  ($str ^ $copy) =~ /^\0*/;
  return wantarray  ? ($cycleLen, substr $str, 0, $cycleLen)
                    : $cycleLen if $+[0] == $strLen;
  }