IPv6::compress( string $ip ): string

97    public static function compress(string $ip)98    {99        // Prepare the IP to be compressed100        $ip = self::uncompress($ip);101        $ip_parts = self::split_v6_v4($ip);102 103        // Replace all leading zeros104        $ip_parts[0] = (string) preg_replace('/(^|:)0+([0-9])/', '\1\2', $ip_parts[0]);105 106        // Find bunches of zeros107        if (preg_match_all('/(?:^|:)(?:0(?::|$))+/', $ip_parts[0], $matches, PREG_OFFSET_CAPTURE)) {108            $max = 0;109            $pos = null;110            foreach ($matches[0] as $match) {111                if (strlen($match[0]) > $max) {112                    $max = strlen($match[0]);113                    $pos = $match[1];114                }115            }116 117            assert($pos !== null, 'For PHPStan: Since the regex matched, there is at least one match. And because the pattern is non-empty, the loop will always end with $pos ≥ 1.');118            $ip_parts[0] = substr_replace($ip_parts[0], '::', $pos, $max);119        }120 121        if ($ip_parts[1] !== '') {122            return implode(':', $ip_parts);123        }124 125        return $ip_parts[0];126    }