自己写的php中文截取函数mb_strlen和mb_substr

if ( !function_exists('mb_strlen') ) {
?function mb_strlen ($text,$encode) {
??if ($encode=='UTF-8') {
???return preg_match_all('%(?:
?????? [x09x0Ax0Dx20-x7E]?????????? # ASCII
?????| [xC2-xDF][x80-xBF]??????????? # non-overlong 2-byte
?????|? xE0[xA0-xBF][x80-xBF]?????? # excluding overlongs
?????| [xE1-xECxEExEF][x80-xBF]{2} # straight 3-byte
?????|? xED[x80-x9F][x80-xBF]?????? # excluding surrogates
?????|? xF0[x90-xBF][x80-xBF]{2}??? # planes 1-3
?????| [xF1-xF3][x80-xBF]{3}???????? # planes 4-15
?????|? xF4[x80-x8F][x80-xBF]{2}??? # plane 16
?????)%xs',$text,$out);
??}else{
???return strlen($text);
??}
?}
}

/* from Internet,author unknown */
if (!function_exists('mb_substr')) {
??? function mb_substr($str,$start,$len = '',$encoding="UTF-8"){
??????? $limit = strlen($str);
?
??????? for ($s = 0; $start > 0;--$start) {// found the real start
??????????? if ($s >= $limit)
??????????????? break;
?
??????????? if ($str[$s] <= "x7F")
??????????????? ++$s;
??????????? else {
??????????????? ++$s; // skip length
?
??????????????? while ($str[$s] >= "x80" && $str[$s] <= "xBF")
??????????????????? ++$s;
??????????? }
??????? }
?
??????? if ($len == '')
??????????? return substr($str,$s);
??????? else
??????????? for ($e = $s; $len > 0; --$len) {//found the real end
??????????????? if ($e >= $limit)
??????????????????? break;
?
??????????????? if ($str[$e] <= "x7F")
??????????????????? ++$e;
??????????????? else {
??????????????????? ++$e;//skip length
?
??????????????????? while ($str[$e] >= "x80" && $str[$e] <= "xBF" && $e < $limit)
??????????????????????? ++$e;
??????????????? }
??????????? }
?
??????? return substr($str,$s,$e - $s);
??? }
}
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