Why does right shift in PHP return a negative number?

Question

I am trying to query a bittorrent tracker and am using unpack to get the list of IPs from the response. So, something like this:

$ip = unpack("N", $peers);
$ip_add = ($ip[1]>>24) . "." . (($ip[1]&0x00FF0000)>>16) . "." . (($ip[1]&0x0000FF00)>>8) . "." . ($ip[1]&0x000000FF);

But, for some reason, I am getting the following IP addresses when I print $ip_add:

117.254.136.66
121.219.20.250
-43.7.52.163

Does anyone know what could be going wrong?

Answer 1

use long2ip() to transform number back into ip

Answer 2

As zerkms says, long2ip does what you want. To answer your question, >> is an arithmetic right shift (so named because $i >> $j is equivalent to the arithmetic expression i / 2j), which propagates the sign bit to preserve the sign of the number. That is, $i < 0 iff ($i >> $j) < 0. PHP doesn't have a logical shift (but you could define your own).