Busca a menor máscara possível em uma lista de CIDRs

index.php

<?php

class IPv4Subnet
{
    private $address, $mask;

    function __construct($ip)
    {
        list($this->address, $this->mask) = $this->toBin($ip);
    }

    public function within($ip)
    {
        list($subjectAddress, $subjectMask) = $this->toBin($ip);

        return $this->mask !== $subjectMask &&
            ($this->mask | ($this->mask ^ $subjectMask)) === $this->mask &&
            ($this->address & $subjectMask) === $subjectAddress;
    }

    private function toBin($ip)
    {
        preg_match('#([0-9]+)\.([0-9]+)\.([0-9]+)\.([0-9]+)\/([0-9]+)#is', $ip, $bytes);

        $base = ~((~0 << 16) << 16);
        $mask = $base << (32 - $bytes[5]);

        $mask    = pack('C*', $mask >> 24 & 0xFF, $mask >> 16 & 0xFF, $mask >> 8 & 0xFF, $mask & 0xFF);
        $address = pack('C*', $bytes[1], $bytes[2], $bytes[3], $bytes[4]) & $mask;

        return [$address, $mask];
    }
}

$list = file('list.txt');

$result = [];

foreach ($list as $ip) {
    $cidr = new IPv4Subnet($ip);
    $result[$ip] = 1;

    foreach ($list as $compare) {
        if ($cidr->within($compare)) {
            unset($result[$ip]);
            break;
        }
    }
}

$result = array_keys($result);

file_put_contents('final.txt', implode($result));