Case-Sensitive Alphanumeric Increment Function

<?php

$time = microtime(true);

$x = 10000000;

$string = '://aoeuaosreducraouasrocduouhecudsroeudraoheucoreuoeu';

for ($i = 0; $i < $x; $i++) {
    if (strpos($string, 'http') === 0) {
    }
}

echo ((microtime(true) - $time) / $x) . PHP_EOL;

$time = microtime(true);

for ($i = 0; $i < $x; $i++) {
    if (substr($string, 0, 4) == 'http') {
    }
}

echo ((microtime(true) - $time) / $x) . PHP_EOL;