/**
* Return a contiguous list of true CIDR blocks that span the range given.
*
* Note: It's not a good idea to call this with IPv6 addresses. While it may
* work for certain ranges this can be very slow. Also an IPv6 list won't be
* as accurate as an IPv4 list.
*
* @example
* range_to_cidrlist(192.168.0.0, 192.168.0.15) ==
* 192.168.0.0/28
* range_to_cidrlist(192.168.0.0, 192.168.0.20) ==
* 192.168.0.0/28
* 192.168.0.16/30
* 192.168.0.20/32
*/
public static function range_to_cidrlist($start, $end)
{
$ver = false === filter_var($start, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4) ? 6 : 4;
$start = IP::inet_ptod($start);
$end = IP::inet_ptod($end);
$len = $ver == 4 ? 32 : 128;
$log2 = $ver == 4 ? log(2) : BC::bclog(2);
$list = array();
while (BC::cmp($end, $start) >= 0) {
// $end >= $start
$prefix = self::max_prefix(IP::inet_dtop($start), $len);
if ($ver == 4) {
$diff = $len - floor(log($end - $start + 1) / $log2);
} else {
// this is not as accurate due to the bclog function
$diff = bcsub($len, BC::bcfloor(bcdiv(BC::bclog(bcadd(bcsub($end, $start), '1')), $log2)));
}
if ($prefix < $diff) {
$prefix = $diff;
}
$list[] = IP::inet_dtop($start) . "/" . $prefix;
if ($ver == 4) {
$start += pow(2, $len - $prefix);
} else {
$start = bcadd($start, bcpow(2, $len - $prefix));
}
}
return $list;
}