Benchmarking "strlen($string) > 25" vs "isset($string[25])" for speed

strlen_benchmark.php

<?php

/**
 * @param array $functions  An associative array of closures to benchmark
 * @param int   $iterations The number of iterations
 */
function benchmark($functions, $iterations)
{
    foreach ($functions as $name => $function) {
        $start = microtime(true);

        for ($i = 0; $i < $iterations; $i++) {
            call_user_func($function);
        }

        $delta = microtime(true) - $start;

        echo "$name: " . $delta . "\n";
    }
}

// Fill an array with 10000 strings 1 to 32 chars long
$data = array_fill(1, 10000, substr(md5(rand()), 0, rand(1, 32)));

$functions = array(
    'strlen' => function () use ($data) {
        foreach ($data as $d) {
            $result = (strlen($d) > 25);
        }
    },
    'isset' => function () use ($data) {
        foreach ($data as $d) {
            $result = isset($d[25]);
        }
    }
);


echo "Benchmarking \"strlen(\$string) > 25\" vs \"isset(\$string[25])\" ...\n";

benchmark($functions, 10000);

Results on an iMac 2.7 GHz Intel Core i5 with 12GB RAM with PHP 5.6.4 (less is better)

strlen: 18.526916980743
isset: 9.9106788635254