Arkadaşlar admin girişi yaparken bu hatayı alıyorum

Fatal error: Call to undefined function return_bytes() in /home/public_html/admin/functions.php on line 1558

hatanın bulunudu yer :

function get_true_max_filesize()
{
$upload_max_filesize = return_bytes(ini_get('upload_max_filesize'));
$post_max_size = return_bytes(ini_get('post_max_size'));
// uploads shouldn't exceed the size limit of the total post
$post_max_size = (70 * $post_max_size) / 100;

$max_size = 0;
$max_size = ($upload_max_filesize < $post_max_size) ? $upload_max_filesize : $post_max_size;

return $max_size;
}

yardımlarınızı bekliyorum.