<?php

$foo = '112312312312323';

$start_time = microtime(true);

for ($i = 0; $i < 10000; $i++) {
    $foo = $foo.'1';
    preg_match('/^[a-zA-Z0-9]+$/', $foo);
}

$end_time = microtime(true);

echo 'preg_match Result: ' . ($end_time - $start_time).PHP_EOL;

$foo = '112312312312323';

$start_time = microtime(true);

for ($i = 0; $i < 10000; $i++) {
    $foo = $foo.'1';
    ctype_alnum($foo);
}

$end_time = microtime(true);

echo 'ctype Result: ' . ($end_time - $start_time).PHP_EOL;