Benchmark a PHP function

benchmark.php

<?php

$calibration = benchmark(function() { });
$benchmark = benchmark(function() {
    sleep(1);
});

echo "Calibration run: ".number_format($calibration)."/sec\n";
echo "Benchmark run: ".number_format($benchmark)."/sec\n";
echo 'Approximate code execution time (seconds): '.number_format((1/$benchmark) - (1/$calibration), 10);

function benchmark($x)
{
    $start = $t = microtime(true);
    $total = $c = $loop = 0;

    while (true) {
        $x();
        $c++;

        $now = microtime(true);
        if ($now - $t > 1) {
            $loop++;
            $total += $c;
            list($t, $c) = array(microtime(true), 0);
        }

        if ($now - $start > 2) {
            return round($total / $loop);
        }
    }
}