php format file size

/**
 * 格式化文件大小
 * @param int $size
 * @return varchar
 */
function formatsize($size)
{
    $prec=3;
    $size = round(abs($size));
    $units = array(0 => " B", 1 => " KB", 2 => " MB", 3 => " GB", 4 => " TB");
    if ($size==0)
    {
        return str_repeat(" ", $prec) . "0" . $units[0];
    }
    $unit = min(4, floor(log($size) / log(2) / 10));
    $size = $size * pow(2, -10 * $unit);
    $digi = $prec - 1 - floor(log($size) / log(10));
    $size = round($size * pow(10, $digi)) * pow(10, -$digi);
    return $size . $units[$unit];
}