How can I improve the processing speed to generate a unique code - php

Question

I need to generate about 100000 unique code. I have tried following code. But it is getting slower. Can anybody suggest me how can I make it faster, soon I have to generate unique code of 1M.
$uniqueArray = array();
for($i = 1; $i <= 100000; $i++) {
$pass = substr(md5(uniqid(mt_rand(), true)) , 0, 6);
if (!in_array($pass, $uniqueArray)) {
$uniqueArray[] = 'AB' . $pass;
}
}

Answer 1

As is, your code is not guaranteed to generate a given amount of unique values. You would need to keep track of the actual number of values in $uniqueArray to be sure.
That said, you can speed up the generation by not searching in the array but by using the array as a map (key => value), e.g.:
<?php
declare(strict_types=1);
error_reporting(-1);
ini_set('display_errors', 'On');
/**
* #return string
*/
function createUniqueCode(): string
{
// ...or any other implementation
return 'AB' . substr(md5(uniqid((string)mt_rand(), true)), 0, 6);
}
$uniqueMap = [];
$n = 10000;
while ($n > 0) {
$pass = createUniqueCode();
if (!isset($uniqueMap[$pass])) {
$uniqueMap[$pass] = true;
$n--;
}
}
$codes = array_keys($uniqueMap);
echo count($codes);

Answer 2

<?php
$count = 100000;
$uniqueArray = range(0,$count-1);
shuffle($uniqueArray);
array_walk($uniqueArray,function(&$v,$k){$v = "AB".sprintf("%06d",$v);});
Runtime <100ms for 100000 values.
Note: If you need the full uniqueness of the values then use the pure uniqueid and dont reduce the results with substr() or other functions.