Checks if ipv6 address is inside a range.

ipv6_cidr.php

<?php
function ipv6_cidr($subnet, $range, $ip)
{
    $bit_mask = mask_bits(128, $range);
    $subnet = inet_pton($subnet) &  $bit_mask;

    return (inet_pton($ip) & $bit_mask) == $subnet;
}

function mask_bits($total_length, $mask_length)
{
    $one_bits = ((int) $mask_length / 8) * 8;
    $part_bits = 8 - ($mask_length % 8);
    $zero_bits = $total_length - $one_bits - 1;

    $mask = str_repeat(chr(0xff), $one_bits / 8) . chr(256 - pow(2, $part_bits)) . str_repeat(chr(0), $zero_bits / 8);
    return $mask;
}