$quant = 15;
$repeat = 10000;

$results[1] = array(); // results of first function
$results[2] = array(); // results of second function

$b = null;

# Durchlauf
for($c=1; $c<=$quant*2; $c++){
  $time['start'] = microtime(true);
  if($c%2) // 1,3,5,...
    for($i=0; $i<$repeat; $i++){
      # first Function
      is_null($b);
      is_null($b);
      is_null($b);
      is_null($b);
      is_null($b);
      is_null($b);
      is_null($b);
      is_null($b);
      is_null($b);
      is_null($b);
      is_null($b);
      is_null($b);
    }
  else // 2,4,6,...
    for($i=0; $i<$repeat; $i++){
      # second Function
      $b===NULL;
      $b===NULL;
      $b===NULL;
      $b===NULL;
      $b===NULL;
      $b===NULL;
      $b===NULL;
      $b===NULL;
      $b===NULL;
      $b===NULL;
      $b===NULL;
      $b===NULL;
    }
  $time['end'] = microtime(true);
  $results[!($c%2)+1][] = $time['end']-$time['start'];
}


$leerlaufres = array(); // results of empty for()-loop
for($c=1; $c<=$quant*2; $c++){ # Leerlauf messen
  $time['start'] = microtime(true);
  if($c%2) // 1,3,5,...
    for($i=0; $i<$repeat; $i++){}
  else // 2,4,6,...
    for($i=0; $i<$repeat; $i++){}
  $time['end'] = microtime(true);
  $leerlaufres[] = $time['end']-$time['start'];
}
$leerlaufres = array_sum($leerlaufres)/$quant/2;


$average[1] = (array_sum($results[1])/($quant-1)-$leerlaufres)*1000; // ms 1 func
$average[2] = (array_sum($results[2])/($quant-1)-$leerlaufres)*1000; // ms 2 func