<?php
/*check repetition at any point in the strings*/
function checkRepetition($string1, $string2) {
  if (($length = strlen($string1)) != strlen($string2)) {
    return false;
  }
  $pos1 = 0;
  while ($pos1 < $length) {
    $pos2 = 0;
    while ($pos2 < $length) {
      if (substr($string1, $pos1, 1) == substr($string2, $pos2, 1)) {
        $maxRepetition = max($maxRepetition, checkLengthOfRepetition(substr($string1, $pos1), substr($string2, $pos2)));
      }
      $pos2++;
    }
    $pos1++;
  }
  return $maxRepetition;
}

/*check repetition of the first few chars*/
function checkLengthOfRepetition($string1, $string2) {
  global $_cr_instances;
  global $_cr_repetitions;
  if (!$_cr_instances) {
    $_cr_repetitions = 0;
  }
  $_cr_instances++;
  if (strlen($string1) == 0) {
    $_cr_instances--;
    return $_cr_repetitions;
  }
  elseif (substr($string1, 0, 1) == substr($string2, 0, 1)) {
    $_cr_repetitions++;
    $rtnVal = checkLengthOfRepetition(substr($string1, 1), substr($string2, 1));
    $_cr_instances--;
    return $rtnVal;
  }
  else {
    $_cr_instances--;
    return $_cr_repetitions;
  }
}

/*let's find some md5 recurrences!*/
$current = md5(rand());
while (true) {
  if (($blah = checkRepetition($current, $new = md5($current))) > 4) {
    echo $current . ' ' . $new . ' ' . $blah . chr(10);
  }
  $current = $new;
}
?>