Question

I’ve been given the following PHP function and asked to write another function that reverses it.

function convertTo16bit($ipString) {
    $ipString = explode(".", $ipString);

    $ip = ($ipString[0] << 24) | ($ipString[1] << 16) | ($ipString[2] << 8) | ($ipString[3]);
    $lowNumber = $ip & 0xffff;
    $highNumber = ($ip >> 16) & 0xffff;
    return array($lowNumber , $highNumber );
}

First Question: I understand what the above code is doing but not why, can someone explain why you would need to create a lowNumber and highNumber for example?

Secondly, I need to write a function called “convertToIPAddress” which takes an array similar to the one outputted above and return a string in the form of an IP address. Can anyone point me in the right direction?

Thanks

Answer 1

I figured it out…

function convert16BitIntsToIP($startingArray) {
    $low = $startingArray[0];
    $high  = $startingArray[1];

    $base = $high << 16 | $low;

    $ip1 = $base >> 24 & 0x00ff;
    $ip2 = $base >> 16 & 0x00ff;
    $ip3 = $base >> 8 & 0x00ff;
    $ip4 = $base & 0x00ff;

    $ip = "$ip1.$ip2.$ip3.$ip4";

   return $ip;
   }