mlocati / ip-lib

    public function getReverseDNSLookupName()

    {

        switch ($this->getAddressType()) {

            case AddressType::T_IPv4:

                $unitSize = 8; // bytes

                $maxUnits = 4;

                $isHex = false;

                $rxUnit = '\d+';

                break;

            case AddressType::T_IPv6:

                $unitSize = 4; // nibbles

                $maxUnits = 32;

                $isHex = false;

                $rxUnit = '\d+';

                break;

            case AddressType::T_IPv6:

                $unitSize = 4; // nibbles

                $maxUnits = 32;

                $isHex = true;

                $rxUnit = '[0-9A-Fa-f]';

                break;

        }

        $totBits = $unitSize * $maxUnits;

        $prefixUnits = (int) ($this->networkPrefix / $unitSize);