Change endianness of a decimal number in PHP

num_endianness.php

<?php

/**
 * Change endianness of the given decimal number.
 *
 * @param int $num
 *
 * @return int
 */
function num_endianness($num) {
    $hex = dechex($num);

    if (strlen($hex) <= 2) {
        return $num;
    }
    
    return hexdec(unpack('H*', strrev(pack('H*', $hex)))[1]);
}