PHP diff

function diff($old, $new){
    $matrix = array();
    $maxlen = 0;
    foreach($old as $oindex => $ovalue){
        $nkeys = array_keys($new, $ovalue);
        foreach($nkeys as $nindex){
            $matrix[$oindex][$nindex] = isset($matrix[$oindex - 1][$nindex - 1]) ?
                $matrix[$oindex - 1][$nindex - 1] + 1 : 1;
            if($matrix[$oindex][$nindex] > $maxlen){
                $maxlen = $matrix[$oindex][$nindex];
                $omax = $oindex + 1 - $maxlen;
                $nmax = $nindex + 1 - $maxlen;
            }
        }
    }
    if($maxlen == 0) return array(array('d'=>$old, 'i'=>$new));
    return array_merge(
        diff(array_slice($old, 0, $omax), array_slice($new, 0, $nmax)),
        array_slice($new, $nmax, $maxlen),
        diff(array_slice($old, $omax + $maxlen), array_slice($new, $nmax + $maxlen)));
}

function htmlDiff($old, $new){

    // put space in front and behind tags, or they are seen as a word when replacing the one behind it or in front
    $old = str_replace(array("<",">"), array(" <", "> "), $old);
    $new = str_replace(array("<",">"), array(" <", "> "), $new);

    $ret = '';
    $diff = diff(explode(' ', $old), explode(' ', $new));
    foreach($diff as $k){
        if(is_array($k))
            $ret .= (!empty($k['d'])?"<del>".implode(' ',$k['d'])."</del> ":'').
                (!empty($k['i'])?"<ins>".implode(' ',$k['i'])."</ins> ":'');
        else $ret .= $k . ' ';
    }
    return $ret;
}