PHP interception string function sharing, PHP interception string_PHP tutorial

/**
* Method library-intercept string-[The author of this function is unknown]
* @param string $string string
* @param int $length character length
* @param string $dot Whether to add after interception...
* @param string $charset encoding
* @return string
​​*/
    public function cutstr($string, $length, $dot = ' ...', $charset = 'utf-8') {
        if (strlen($string) <= $length) {
            return $string;
        }
        $string = str_replace(array('&', '"', '<', '>'), array('&', '"', '<', '>'), $string);
        $strcut = '';
        if (strtolower($charset) == 'utf-8') {
            $n = $tn = $noc = 0;
            while ($n < strlen($string)) {
                $t = ord($string[$n]);                //ASCIIֵ
                if($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;
            }
            $strcut = substr($string, 0, $n);
        } else {
            for ($i = 0; $i < $length; $i++) {
                $strcut .= ord($string[$i]) > 127 ? $string[$i].$string[++$i] : $string[$i];
            }
}
$strcut = str_replace(array('&', '"', '<', '>'), array('&', '"', '<', '>'), $strcut) ;
          return $strcut.$dot;
}