Centering multibyte string

centeringString.php

<?php

/**
 * Multibyte String Centering
 *
 * Сhanges the received strings centered relative to each other
 *
 * @param string $str1 The first string.
 * @param string $str2 The second string.
 * @param string $encoding The encoding to use, defaults to UTF-8.
 *
 * @return void Returns nothing, all strings are changed by links.
 */
function centering(string &$str1, string &$str2, string $encoding = 'UTF-8')
{
    $len1 = mb_strlen($str1, $encoding);
    $len2 = mb_strlen($str2, $encoding);

    if ($len1 > $len2) {
        $str2 = str_repeat("\x20", ($len1 - $len2) >> 1) . $str2;
    } else if ($len1 < $len2) {
        $str1 = str_repeat("\x20", ($len2 - $len1) >> 1) . $str1;
    }
}

///////////////////// TESTS /////////////////////


$str1 = 'Привет мир!';
$str2 = 'тест тест тест тест';

centering($str1, $str2);

echo $str1 . PHP_EOL . $str2;

//     Привет мир!    
// тест тест тест тест

echo PHP_EOL . PHP_EOL;

$str1 = '充';
$str2 = '煻充Nhiều byte string đệm煻充煻';

centering($str1, $str2);

echo $str1 . PHP_EOL . $str2;

//             充             
// 煻充Nhiều byte string đệm煻充煻