php摘要生成函数(无乱码)

function cutstr($string, $length,$charset,$dot) {//字符，截取长度，字符集，结尾符 
if(strlen($string) <= $length) { 
return $string; 
} 
$pre = chr(1); 
$end = chr(1); 
//保护特殊字符串 
$string = str_replace(array('&', '"', '<', '>'), array($pre.'&'.$end, $pre.'"'.$end, $pre.'<'.$end, $pre.'>'.$end), $string); 
$strcut = ''; 
if(strtolower($charset) == 'utf-8') { 
$n = $tn = $noc = 0; 
while($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; 
} 
$strcut = substr($string, 0, $n); 
} else { 
for($i = 0; $i < $length; $i++) { 
$strcut .= ord($string[$i]) > 127 ? $string[$i].$string[++$i] : $string[$i]; 
} 
} 
//还原特殊字符串 
$strcut = str_replace(array($pre.'&'.$end, $pre.'"'.$end, $pre.'<'.$end, $pre.'>'.$end), array('&', '"', '<', '>'), $strcut); 
//修复出现特殊字符串截段的问题 
$pos = strrpos($s, chr(1)); 
if($pos !== false) { 
$strcut = substr($s,0,$pos); 
} 
return $strcut.$dot; 
}