PHP: マルチバイトへの移行

$strings = [
    "?????",
    "チャーミング",
    "González",
];

foreach ($strings as $string) {
    echo 'strlen:' . strlen($string) . ' vs. mb_strlen:' . mb_strlen($string) . PHP_EOL;
}

echo strpos("チャーミング", "ャ"); // gives 3
echo mb_strpos("チャーミング", "ャ"); // gives 1 because 1st position is 0

echo substr("チャーミング", 3) . PHP_EOL;// ャーミング
echo mb_substr("チャーミング", 3);// ミング

$cnt = 100000;

$strs = [
    'empty' => '',
    'short' => 'zluty kun',
    'short_with_uc' => 'zluty Kun',
    'long' => str_repeat('this is about 10000 chars long string', 270),
    'long_with_uc' => str_repeat('this is about 10000 chars long String', 270),
    'short_utf8' => 'žlutý kůň',
    'short_utf8_with_uc' => 'Žlutý kŮň',
];

foreach ($strs as $k => $str) {
    $a1 = microtime(true);
    for($i=0; $i < $cnt; ++$i){
        $res = strtolower($str);
    }
    $t1 = microtime(true) - $a1;
    // echo 'it took ' . round($t1 * 1000, 3) . ' ms for ++$i'."\n";

    $a2 = microtime(true);
    for($i=0; $i < $cnt; $i++){
        $res = mb_strtolower($str);
    }
    $t2 = microtime(true) - $a2;
    // echo 'it took ' . round($t2 * 1000, 3) . ' ms for $i++'."\n";

    echo 'strtolower is '.round($t2/$t1, 2).'x faster than mb_strtolower for ' . $k . "\n\n";
}