PHP Rating code problem

Hello sir i m having problem regarding my work.
i m having this warning.

Warning: Call-time pass-by-reference has been deprecated - argument passed by value; If you would like to pass it by reference, modify the declaration of ip_valid(). If you would like to enable call-time pass-by-reference, you can set allow_call_time_pass_reference to true in your INI file. However, future versions may not support this any longer. in functions.php on line 68


my code.


1: <?php
2:
3: function insert_rating($rating, $article_id)
4: {
5: if(mysql_num_rows(mysql_query("SELECT ID FROM articles_ratings
6: WHERE rater_ip='".mysql_real_escape_string(getIP())."'
7: AND ID='".mysql_real_escape_string($article_id)."'"))==0)
8: {
9: if(mysql_query("INSERT INTO articles_ratings
10: (`article_id`, `rating_value`, `rater_ip`)
11: VALUES ('".mysql_real_escape_string($article_id)."',
12: '".mysql_real_escape_string($rating)."',
13: '".mysql_real_escape_string(getIP())."')"))
14: {
15: $response = 'Thank you for voting this article!';
16: }
17: else {
18: $response = 'Ups. A problem. I was unable to save your rating!';
19: }
20: }
21: else {
22: $response = 'Sorry but you can only rate once';
23: }
24:
25: $objResponse = new xajaxResponse();
26: $objResponse->addAssign("response","innerHTML", $response);
27: return $objResponse;
28: }
29:
30: function ip_first($ips)
31: {
32: if (($pos = strpos($ips, ',')) != false)
33: {
34: return substr($ips, 0, $pos);
35: }
36: else {
37: return $ips;
38: }
39: }
40:
41: function ip_valid($ips)
42: {
43: if (isset($ips))
44: {
45: $ip = ip_first($ips);
46: $ipnum = ip2long($ip);
47: if ($ipnum !== -1 && $ipnum !== false && (long2ip($ipnum) === $ip))
48: {
49: if (($ipnum < 167772160 || $ipnum > 184549375) &&
50: ($ipnum < -1408237568 || $ipnum > -1407188993) &&
51: ($ipnum < -1062731776 || $ipnum > -1062666241))
52: return true;
53: }
54: }
55: return false;
56: }
57:
58: function getIP()
59: {
60: $check = array(
61: 'HTTP_X_FORWARDED_FOR', 'HTTP_X_FORWARDED', 'HTTP_FORWARDED_FOR',
62: 'HTTP_FORWARDED', 'HTTP_VIA', 'HTTP_X_COMING_FROM', 'HTTP_COMING_FROM',
63: 'HTTP_CLIENT_IP'
64: );
65:
66: foreach ($check as $c)
67: {
68: if (ip_valid(&$_SERVER[$c]))
69: {
70: return ip_first($_SERVER[$c]);
71: }
72: }
73: return $_SERVER['REMOTE_ADDR'];
74: }
75: ?>


plz help me to solve this...:

 

replace
68: if (ip_valid(&$_SERVER[$c]))
with
68: if (ip_valid($_SERVER[$c]))