define('LOOP',1000000);
function f1() {
  ob_start();
  for($i=0; $i<LOOP; ++$i) {
    echo '123456';
    echo '123456';
    echo '123456';
    echo '123456';
    echo '123456';
  }
  ob_end_clean();
}
 
function f2() {
  ob_start();
  for($i=0; $i<LOOP; ++$i) {
    echo "123456";
    echo "123456";
    echo "123456";
    echo "123456";
    echo "123456";
  }
  ob_end_clean();
}
 
$start = microtime(true);
f1();
$stop = microtime(true);
$time1 = $stop - $start;
 
$start = microtime(true);
f2();
$stop = microtime(true);
$time2 = $stop - $start;
 
echo $time1 . "\t";
echo $time2 . "\n";