Generate unique IDs from microtime and calculate collisions

unique_id_microtime.php

<?php
$iterations = 100000;
$orderNrLen = 6;

for ($secondsLen = 0; $secondsLen < 6; $secondsLen++) {
    $numbers = [];
    $collisions = 0;

    for ($i = 0; $i < $iterations; $i++) {
        if ($i % 1000 == 0) sleep(1);

        list($micro, $seconds) = explode(' ', microtime(false));
        $micro = strval(intval($micro * 10000000000));

        $nr = substr($seconds, -$secondsLen) . substr($micro, 0, $orderNrLen = $secondsLen);
        if (!empty($numbers[$nr])) {
            $collisions++;
        } else {
            $numbers[$nr] = $nr;
        }
    }

    echo sprintf("Seconds: %d; collisions: %d [ %.4f%% ]\n", $secondsLen, $collisions, $collisions / $iterations);
    flush();
}