discuz的cutstr函数

function cutstr($string, $length, $dot = ' ...') {
if(strlen($string) <= $length) {
return $string;
}

$pre = chr(1);
$end = chr(1);
$string = str_replace(array('&', '"', '<', '>'), array($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 {
$_length = $length - 1;
for($i = 0; $i < $length; $i++) {
if(ord($string[$i]) <= 127) {
$strcut .= $string[$i];
} else if($i < $_length) {
$strcut .= $string[$i].$string[++$i];
}
}
}

$strcut = str_replace(array($pre.'&'.$end, $pre.'"'.$end, $pre.'<'.$end, $pre.'>'.$end), array('&', '"', '<', '>'), $strcut);

$pos = strrpos($strcut, chr(1));
if($pos !== false) {
$strcut = substr($strcut,0,$pos);
}
return $strcut.$dot;
}