PHP string concatenation benchmark

concat.php

<?php
function starttime() {
    $r = explode( ' ', microtime() );
    $r = $r[1] + $r[0];
    return $r;
}

function endtime($starttime) {
    $r = explode( ' ', microtime() );
    $r = $r[1] + $r[0];
    $r = round($r - $starttime,4);
    return '<strong>Execution Time</strong>: '.$r.' seconds<br />';
}

$times = 100000;

$start = starttime();
$s = ''; $p = 'asdfghjkl';
for($i=0;$i<$times;$i++) {
    $s = $s . '<p>' . $p . '</p>';
}
echo 'String length '.strlen($s).'<br>';
echo 'Concatenation using dot operator ' . endtime($start);

$start = starttime();
$s = ''; $p = 'asdfghjkl';
for($i=0;$i<$times;$i++) {
    $s = "{$s}<p>{$p}</p>";
}
echo 'String length '.strlen($s).'<br>';
echo 'Concatenation using variable expansion ' . endtime($start);


$start = starttime();
$s = ''; $p = 'asdfghjkl';
ob_start();
for($i=0;$i<$times;$i++) {
?><p><?=$p?></p><?php
}
$s = ob_get_clean();
echo 'String length '.strlen($s).'<br>';
echo 'Concatenation using output buffering ' . endtime($start);