discuz是如何判断手机端访问的

function checkmobile() {
    global $_G;
    $mobile = array();
    //各个触控浏览器中$_SERVER['HTTP_USER_AGENT']所包含的字符串数组
    static $touchbrowser_list =array('iphone', 'android', 'phone', 'mobile', 'wap', 'netfront', 'java', 'opera mobi', 'opera mini', 'ucweb', 'windows ce', 'symbian', 'series', 'webos', 'sony', 'blackberry', 'dopod', 'nokia', 'samsung', 'palmsource', 'xda', 'pieplus', 'meizu', 'midp', 'cldc', 'motorola', 'foma', 'docomo', 'up.browser', 'up.link', 'blazer', 'helio', 'hosin', 'huawei', 'novarra', 'coolpad', 'webos', 'techfaith', 'palmsource', 'alcatel', 'amoi', 'ktouch', 'nexian', 'ericsson', 'philips', 'sagem', 'wellcom', 'bunjalloo', 'maui', 'smartphone', 'iemobile', 'spice', 'bird', 'zte-', 'longcos', 'pantech', 'gionee', 'portalmmm', 'jig browser', 'hiptop', 'benq', 'haier', '^lct', '320x320', '240x320', '176x220');
    //window手机浏览器数组【猜的】
    static $mobilebrowser_list =array('windows phone');
    //wap浏览器中$_SERVER['HTTP_USER_AGENT']所包含的字符串数组
    static $wmlbrowser_list = array('cect', 'compal', 'ctl', 'lg', 'nec', 'tcl', 'alcatel', 'ericsson', 'bird', 'daxian', 'dbtel', 'eastcom', 'pantech', 'dopod', 'philips', 'haier', 'konka', 'kejian', 'lenovo', 'benq', 'mot', 'soutec', 'nokia', 'sagem', 'sgh', 'sed', 'capitel', 'panasonic', 'sonyericsson', 'sharp', 'amoi', 'panda', 'zte');
    $pad_list = array('pad', 'gt-p1000');
    $useragent = strtolower($_SERVER['HTTP_USER_AGENT']);
    if(dstrpos($useragent, $pad_list)) {
        return false;
    }
    if(($v = dstrpos($useragent, $mobilebrowser_list, true))){
        $_G['mobile'] = $v;
        return '1';
    }
    if(($v = dstrpos($useragent, $touchbrowser_list, true))){
        $_G['mobile'] = $v;
        return '2';
    }
    if(($v = dstrpos($useragent, $wmlbrowser_list))) {
        $_G['mobile'] = $v;
        return '3'; //wml版
    }
    $brower = array('mozilla', 'chrome', 'safari', 'opera', 'm3gate', 'winwap', 'openwave', 'myop');
    if(dstrpos($useragent, $brower)) return false;
    $_G['mobile'] = 'unknown';
    //对于未知类型的浏览器，通过$_GET['mobile']参数来决定是否是手机浏览器
    if(isset($_G['mobiletpl'][$_GET['mobile']])) {
        return true;
    } else {
        return false;
    }
}

function dstrpos($string, $arr, $returnvalue = false) {
    if(empty($string)) return false;
    foreach((array)$arr as $v) {
        if(strpos($string, $v) !== false) {
        $return = $returnvalue ? $v : true;
        return $return;
    }
}
    return false;
}