What is PHP's mt_rand() minimum value and how to calculate 32 bit interger on 32 bit Linux box

What is the minimum value allowed for mt_rand()? Is it the same value for 32 bit and 64 bit machines? How could I generate a 32 bit integer using mt_rand() (note that it doesn't need to be highly random)?

BACKGROUND WHY I AM ASKING: I have a 64 bit development physical server and a 32 bit production VPS. Just realized the production server was not generating PKs spanning the full range. To figure out what is going on, I ran the following script. The 64 bit machine never (or at least I've never witnessed) matches, but the 32 bit matches about 50% of the time.

<?php

date_default_timezone_set('America/Los_Angeles');
ini_set('display_errors', 1);
error_reporting(E_ALL);

$count=0;
for ($i = 0; $i <= 10000; $i++) {
    $rand=2147483648+mt_rand(-2147483647,2147483647); //Spans 1 to 4294967295 where 0 is reserved
    if($rand==2147483649){$count++;}
}
echo('mt_getrandmax()='.mt_getrandmax().' count='.$count);

output

mt_getrandmax()=2147483647 count=5034