PHP: Differenz zwischen 2 Timestamps berechnen

function date_diff($d1, $d2){
/* This is correctly working time differentiating function. It's resistant to problems with 
   leap year and different days of month. Inputs are two timestamps and function returns array 
   with differences in year, month, day, hour, minute a nd second.
 
   Compares two timestamps and returns array with differencies (year, month, day, hour, minute, second)
 
   More infos at http://de2.php.net/manual/de/function.date-diff.php#93915
*/
        //check higher timestamp and switch if neccessary
        if ($d1 < $d2) {
                $temp = $d2;
                $d2 = $d1;
                $d1 = $temp;
        } else {
                $temp = $d1; //temp can be used for day count if required
        }
        $d1 = date_parse(date("Y-m-d H:i:s",$d1));
        $d2 = date_parse(date("Y-m-d H:i:s",$d2));
        //seconds
        if ($d1['second'] >= $d2['second']){
                $diff['second'] = $d1['second'] - $d2['second'];
        } else {
                $d1['minute']--;
                $diff['second'] = 60-$d2['second']+$d1['second'];
        }
        //minutes
        if ($d1['minute'] >= $d2['minute']){
                $diff['minute'] = $d1['minute'] - $d2['minute'];
        } else {
                $d1['hour']--;
                $diff['minute'] = 60-$d2['minute']+$d1['minute'];
        }
        //hours
        if ($d1['hour'] >= $d2['hour']){
                $diff['hour'] = $d1['hour'] - $d2['hour'];
        } else {
                $d1['day']--;
                $diff['hour'] = 24-$d2['hour']+$d1['hour'];
        }
        //days
        if ($d1['day'] >= $d2['day']){
                $diff['day'] = $d1['day'] - $d2['day'];
        } else {
                $d1['month']--;
                $diff['day'] = date("t",$temp)-$d2['day']+$d1['day'];
        }
        //months
        if ($d1['month'] >= $d2['month']){
                $diff['month'] = $d1['month'] - $d2['month'];
        } else {
                $d1['year']--;
                $diff['month'] = 12-$d2['month']+$d1['month'];
        }
        //years
        $diff['year'] = $d1['year'] - $d2['year'];
        return $diff;   
}

define(BIRTHDAY, strtotime('1980-08-26 15:25:00')); // geburtsdatum
$now  = time(); // aktuelles datum
 
// geburtsdatum dieses jahr:
$birthdayThisYear = mktime(date('H',BIRTHDAY),date('i',BIRTHDAY),date('s',BIRTHDAY),date('n',BIRTHDAY),date('j',BIRTHDAY),date('Y',$now));
 
// geburtsdatum nächstes jahr:
$birthdayNextYear = mktime(date('H',BIRTHDAY),date('i',BIRTHDAY),date('s',BIRTHDAY),date('n',BIRTHDAY),date('j',BIRTHDAY),date('Y',$now)+1);
 
// geburtsdatum letztes jahr:
$birthdayLastYear = mktime(date('H',BIRTHDAY),date('i',BIRTHDAY),date('s',BIRTHDAY),date('n',BIRTHDAY),date('j',BIRTHDAY),date('Y',$now)-1);                                                                                                                              
 
// der nächste geburtstag:
$nextBirthday     = ($now<$birthdayThisYear)?$birthdayThisYear:$birthdayNextYear;                           
 
// der letzte geburtstag:
$lastBirthday     = ($now<=$birthdayThisYear)?$birthdayLastYear:$birthdayThisYear;
 
// wie viel prozent des jahres bis zum nächsten geburtstag sind schon um? 
$percent          = ($now-$lastBirthday) / ($nextBirthday-$lastBirthday) * 100;
 
// wie viele tage sind es noch bis zum nächsten geburtstag?
$days2Birthday    = floor(($nextBirthday - $now) / 86400);
 
// alter als array  (jahre, monate, tage, stunden, minuten, sekunden - schaltjahre werde berücksichtigt!)
$age              = date_diff(BIRTHDAY, $now);