PHP substr이 한자의 절반을 잘못된 문자로 자르는 문제에 대한 솔루션

/**
* 改进的substr
* edit bbs.it-home.org
*/
function getstr($string, $length, $encoding  = 'utf-8') {
$string = trim($string);
    if($length && strlen($string) > $length) {
            //截断字符
            $wordscut = '';
            if(strtolower($encoding) == 'utf-8') {
                //utf8编码
                $n = 0;
                $tn = 0;
                $noc = 0;
                while ($n < strlen($string)) {
                    $t = ord($string[$n]);
                    if($t == 9 || $t == 10 || (32 <= $t && $t <= 126)) {
                        $tn = 1;
                        $n  ;
                        $noc  ;
                    } elseif(194 <= $t && $t <= 223) {
                        $tn = 2;
                        $n  = 2;
                        $noc  = 2;
                    } elseif(224 <= $t && $t < 239) {
                        $tn = 3;
                        $n  = 3;
                        $noc  = 2;
                    } elseif(240 <= $t && $t <= 247) {
                        $tn = 4;
                        $n  = 4;
                        $noc  = 2;
                    } elseif(248 <= $t && $t <= 251) {
                        $tn = 5;
                        $n  = 5;
                        $noc  = 2;
                    } elseif($t == 252 || $t == 253) {
                        $tn = 6;
                        $n  = 6;
                        $noc  = 2;
                    } else {
                        $n  ;
                    }
                    if ($noc >= $length) {
                        break;
                    }
                }
                if ($noc > $length) {
                    $n -= $tn;
                }
                $wordscut = substr($string, 0, $n);
            } else {
                for($i = 0; $i < $length - 1; $i  ) {
                    if(ord($string[$i]) > 127) {
                        $wordscut .= $string[$i].$string[$i   1];
                        $i  ;
                    } else {
                        $wordscut .= $string[$i];
                    }
                }
            }
            $string = $wordscut;
        }
        return trim($string);
    }
  ?>