PHP puzzler

gistfile1.php

$size = 512*1024;
$keys = range(1, $size);
//shuffle($keys);

$arr = [];
foreach ($keys as $k) {
	$arr[$k] = $k;
}

$s = microtime(1);

for ($round = 0; $round < 200; $round++) {
	for ($i = 1; $i < $size; $i++) {
		$arr[$i];
	}
}

echo microtime(1) - $s, "\n";

// PHP 5
// without shuffle     4.7s
// with shuffle       14.1s
//
// PHP 7
// without shuffle     2.6s
// with shuffle        8.4s