PHP判断是否为手机访问

/**
 * 判断是否为手机访问
 * @return  boolean
 */
function sp_is_mobile() {
	static $sp_is_mobile;

	if ( isset($sp_is_mobile) )
		return $sp_is_mobile;

	if ( empty($_SERVER['HTTP_USER_AGENT']) ) {
		$sp_is_mobile = false;
	} elseif ( strpos($_SERVER['HTTP_USER_AGENT'], 'Mobile') !== false // many mobile devices (all iPhone, iPad, etc.)
			|| strpos($_SERVER['HTTP_USER_AGENT'], 'Android') !== false
			|| strpos($_SERVER['HTTP_USER_AGENT'], 'Silk/') !== false
			|| strpos($_SERVER['HTTP_USER_AGENT'], 'Kindle') !== false
			|| strpos($_SERVER['HTTP_USER_AGENT'], 'BlackBerry') !== false
			|| strpos($_SERVER['HTTP_USER_AGENT'], 'Opera Mini') !== false
			|| strpos($_SERVER['HTTP_USER_AGENT'], 'Opera Mobi') !== false ) {
		$sp_is_mobile = true;
	} else {
		$sp_is_mobile = false;
	}

	return $sp_is_mobile;
}