Determining if an IP is within a specific range: redux

I was reading Paul Gregg’s very clear explanation of “classless” ranges comparison when I realized that his code was not as “bare metal” as could be.So, here is the code I’ve been using in nextBBS.It only accepts ranges in the form “x.x.x.x/b” but it’s short and all I needed, really.

function isSubnet($subnet, $ip) {
    // Classless (in more than one way) comparison
    $cursubnet = explode('/', $subnet);
    $longsubnet = ip2long($cursubnet[0]);
    $longip = ip2long($ip);
    if(count($cursubnet){
        // Compare IP itself
        return ($longip==$longsubnet);
    }
    // IPv4 only!
    $subnetmask = 0xffffffff << (32-$cursubnet[1]);
    return (($longip & $subnetmask) == ($longsubnet & $subnetmask));
}