让CodeIgniter的ellipsize()支持中文截断的方法

function ellipsize($codepage = 'UTF-8',
                   $str, $max_length, $position = 1, $ellipsis = '…')
{
    // Strip tags
    $str = trim(strip_tags($str));

    // Is the string long enough to ellipsize?
    if (mb_strlen($str, $codepage) <= $max_length)
    {
        return $str;
    }

    $beg = mb_substr($str, 0, floor($max_length $position), $codepage);

    $position = ($position > 1) ? 1 : $position;

    if ($position === 1)
    {
        $end = mb_substr($str, 0,
            -($max_length - mb_strlen($beg, $codepage)), $codepage);
    }
    else
    {
        $end = mb_substr($str,
            -($max_length - mb_strlen($beg, $codepage)), $max_length, $codepage);
    }

    return $beg.$ellipsis.$end;
}