public static function bytes($bytes, $precision = 2)
{
$units = array('b', 'KiB', 'MiB', 'GiB', 'TiB');
$bytes = max($bytes, 0);
$pow = floor(($bytes ? log($bytes) : 0) / log(1024));
$pow = min($pow, count($units) - 1);
$bytes /= 1 << 10 * $pow;
return round($bytes, $precision) . ' ' . $units[$pow];
}