PHP 判断访问来自手机端还是PC端

/**
 * //判断是否手机设备
 * @return boolean
 */
function is_mobile_request()
{
  $_SERVER['ALL_HTTP'] = isset($_SERVER['ALL_HTTP']) ? $_SERVER['ALL_HTTP'] : '';
  $mobile_browser = '0';
  if(preg_match('/(up.browser|up.link|mmp|symbian|smartphone|midp|wap|phone|iphone|ipad|ipod|android|xoom)/i', strtolower($_SERVER['HTTP_USER_AGENT'])))
    $mobile_browser++;
  if((isset($_SERVER['HTTP_ACCEPT'])) and (strpos(strtolower($_SERVER['HTTP_ACCEPT']),'application/vnd.wap.xhtml+xml') !== false))
    $mobile_browser++;
  if(isset($_SERVER['HTTP_X_WAP_PROFILE']))
    $mobile_browser++;
  if(isset($_SERVER['HTTP_PROFILE']))
    $mobile_browser++;
  $mobile_ua = strtolower(substr($_SERVER['HTTP_USER_AGENT'],0,4));
  $mobile_agents = array(
      'w3c ','acs-','alav','alca','amoi','audi','avan','benq','bird','blac',
      'blaz','brew','cell','cldc','cmd-','dang','doco','eric','hipt','inno',
      'ipaq','java','jigs','kddi','keji','leno','lg-c','lg-d','lg-g','lge-',
      'maui','maxo','midp','mits','mmef','mobi','mot-','moto','mwbp','nec-',
      'newt','noki','oper','palm','pana','pant','phil','play','port','prox',
      'qwap','sage','sams','sany','sch-','sec-','send','seri','sgh-','shar',
      'sie-','siem','smal','smar','sony','sph-','symb','t-mo','teli','tim-',
      'tosh','tsm-','upg1','upsi','vk-v','voda','wap-','wapa','wapi','wapp',
      'wapr','webc','winw','winw','xda','xda-'
  );
  if(in_array($mobile_ua, $mobile_agents))
    $mobile_browser++;
  if(strpos(strtolower($_SERVER['ALL_HTTP']), 'operamini') !== false)
    $mobile_browser++;
  // Pre-final check to reset everything if the user is on Windows
  if(strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'windows') !== false)
    $mobile_browser=0;
  // But WP7 is also Windows, with a slightly different characteristic
  if(strpos(strtolower($_SERVER['HTTP_USER_AGENT']), 'windows phone') !== false)
    $mobile_browser++;
  if($mobile_browser>0)
    return "mobile";
  else
    return "pc";
}