php: ip2long returning negative val

Question

hi,

function ip_address_to_number($IPaddress) { 
 if(!$IPaddress) {
  return false;
 } else {
  $ips = split('\.',$IPaddress);
  return($ips[3] + $ips[2]*256 + $ips[1]*65536 + $ips[0]*16777216);
 }
}

that function executes the same code as the php bundled function ip2long. however, when i print these 2 values, i get 2 different returns. why? (im using php 5.2.10 on a wamp environment).

ip2long('200.117.248.17'); //returns -931792879

ip_address_to_number('200.117.248.17'); // returns 3363174417

Applied and continued here: http://stackoverflow.com/questions/3063192/php-showing-my-country-based-on-my-ip-mysql-optimized

Answer 1

Try this instead:

$ip = sprintf('%u', ip2long($_SERVER['REMOTE_ADDR']));

sprintf will then write it as an unsigned integer.

Answer 2

glopes@nebm:~$ php -r "printf('%u', -931792879);"
3363174417

There you go. My guess is that you are on a system with 32-bit ints and your ip_address_to_number is actually returning a float.

You see, with 32-bit ints, your maximum positive integer is (2^31) - 1 = 2 147 483 647, so the integer wraps around.

If you want to mimic the behaviour of the PHP function, do:

function ip_address_to_number($IPaddress) { 
 if(!$IPaddress) {
  return false;
 } else {
  $ips = split('\.',$IPaddress);
  return($ips[3] | $ips[2] << 8 | $ips[1] << 16 | $ips[0] << 24);
 }
}

(by the way, split has been deprecated)

Answer 3

  $ips[3]                             = 17
+ $ips[2] * 256 = 248 * 256           = 63488
+ $ips[1] * 65536 = 117 * 65536       = 7667712
+ $ips[0] * 16777216 = 200 * 16777216 = 3355443200
                                      = 3363174417

PHP max integer value (32-bit) is 2147483647, which is < 3363174417

Quoting from the ip2long() PHP manual page

Note: Because PHP's integer type is signed, and many IP addresses will result in negative integers, you need to use the "%u" formatter of sprintf() or printf() to get the string representation of the unsigned IP address.