PHPで単語数によってインターセプトして置換する方法

function substr_format($text, $length, $replace='..', $encoding='UTF-8') 
{
if ($text && mb_strlen($text, $encoding)>$length)
{
return mb_substr($text, 0, $length, $encoding).$replace;
}
return $text;
}

function cut_string($str, $len)
{
// 检查长度
if (mb_strwidth($str, &#39;UTF-8&#39;)<=$len)
{
return $str;
}
// 截取
$i = 0;
$tlen = 0;
$tstr = &#39;&#39;;
while ($tlen < $len)
{
$chr = mb_substr($str, $i, 1, &#39;UTF-8&#39;);
$chrLen = ord($chr) > 127 ? 2 : 1;
if ($tlen + $chrLen > $len) break;
$tstr .= $chr;
$tlen += $chrLen;
$i ++;
}
if ($tstr != $str)
{
$tstr .= &#39;...&#39;;
}
return $tstr;
}