/**
* Return the network mask for the prefix given.
*
* Normally this is only useful for IPv4 addresses but you can generate a
* mask for IPv6 addresses as well, only because its mathematically
* possible.
*
* @param integer $prefix CIDR prefix bits (0-128)
* @param integer $version IP version. If null the version will be detected
* based on the prefix length given.
*/
public static function prefix_to_mask($prefix, $version = null)
{
if ($version === null) {
$version = $prefix > 32 ? 6 : 4;
}
if ($prefix < 0 or $prefix > 128) {
throw new \InvalidArgumentException("Invalid prefix length \"{$prefix}\"");
}
if ($version != 4 and $version != 6) {
throw new \InvalidArgumentException("Invalid version \"{$version}\". Must be 4 or 6");
}
if ($version == 4) {
return long2ip($prefix == 0 ? 0 : 0xffffffff >> 32 - $prefix << 32 - $prefix);
} else {
return IP::inet_dtop($prefix == 0 ? 0 : BC::bcleft(BC::bcright(BC::MAX_UINT_128, 128 - $prefix), 128 - $prefix));
}
}
