PHP benchmark with heap sort

<?php

define('N', 10000000);

$h = array_fill(0, N, 0);

main();

function down($pos, $n) {
    global $h;
    while (true) {
        $j = 2 * $pos + 1;
        if ($j >= $n) {
            break;
        }
        if ($j + 1 < $n && $h[$j + 1] > $h[$j]) {
            $j++;
        }
        $t = $h[$pos];
        if ($t >= $h[$j]) {
            break;
        }
        $h[$pos] = $h[$j];
        $h[$j] = $t;
        $pos = $j;
    }
}

function main() {
    global $h;

    $start = round(microtime(true) * 1000);

    for ($i = 0; $i < N; $i++) {
        $h[$i] = $i;
    }

    for ($i = (int) (N / 2); $i >= 0; $i--) {
        down($i, N);
    }

    $n = N;

    while ($n > 1) {
        $n--;
        $t = $h[0];
        $h[0] = $h[$n];
        $h[$n] = $t;
        down(0, $n);
    }

    foreach ($h as $i => $v) {
        if ($i !== $v) {
            echo "Sorting failed at index $i!\n";
            return;
        }
    }

    $finish = round(microtime(true) * 1000);
    $delta = $finish - $start;

    echo "Done in $delta ms!\n";
}