dedecms怎么重新定义cn_substr函数截取字数更准确

/** 
* 中英文截取字符串，汉字安2个字节 
* 
* @access public 
* @param string $str 需要截取的字符串 
* @param int $cutLen 截取的长度 
* @param bool $cutSlashes 是否去掉\ 
* @param bool $addSlashes 是加\ 
* @param string $oDot 截取后加的字符串，如经常用的三个点 
* @param bool $hasHtml 是否有html 
* @return string 
*/ 
if ( ! function_exists(‘cn_substr’)){ 
function cn_substr($str, $cutLen, $oDot = null, $hasHtml = false, $cutSlashes = false, $addSlashes = false) { 
global $cfg_soft_lang; 
$str = trim ( $str ); 
if ($cutSlashes) $str = stripslashes ( $str ); 
if($hasHtml){ 
$str = preg_replace ( “/(\<[^\<]*\>|\r|\n|\s|\[.+?\])/is”, ‘ ‘, $str ); 
$str = htmlspecialchars ( $str ); 
}else{ 
$str = htmlspecialchars ( $str ); 
} 
if ($cutLen && strlen ( $str ) > $cutLen) { 
$nStr = ”; 
if ($cfg_soft_lang == ‘utf-8′) { 
$n = 0; 
$tn = 0; 
$noc = 0; 
while ( $n < strlen ( $str ) ) { 
$t = ord ( $str [$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 >= $cutLen)break; 
} 
if ($noc > $cutLen) $n -= $tn; 
$nStr = substr ( $str, 0, $n ); 
} else { 
for($i = 0; $i < $cutLen – 1; $i ++) { 
if (ord ( $str [$i] ) > 127) { 
$nStr .= $str [$i] . $str [$i + 1]; 
$i ++; 
} else { 
$nStr .= $str [$i]; 
} 
} 
} 
$str = $nStr . $oDot; 
} 
if ($addSlashes) $str = addslashes ( $str ); 
$str = htmlspecialchars_decode ( $str ); 
return trim ( $str ); 
} 
}