Does about 15 MiB/s on my machine

mtrandout.php

#!/usr/bin/env php
<?php

mt_srand(random_int(PHP_INT_MIN, PHP_INT_MAX));

while (true) {
    $a = [];
    for ($i = 0; $i < 10000; $i++) {
        $a[] = mt_rand_short();
    }
    echo pack("s*", ...$a);
}

function mt_rand_short() : int {
    return mt_rand(-2**15, 2**15 - 1);
}