Jetpack::staticize_subdomain PHP Method

    public static function staticize_subdomain($url)
    {
        // Extract hostname from URL
        $host = parse_url($url, PHP_URL_HOST);
        // Explode hostname on '.'
        $exploded_host = explode('.', $host);
        // Retrieve the name and TLD
        if (count($exploded_host) > 1) {
            $name = $exploded_host[count($exploded_host) - 2];
            $tld = $exploded_host[count($exploded_host) - 1];
            // Rebuild domain excluding subdomains
            $domain = $name . '.' . $tld;
        } else {
            $domain = $host;
        }
        // Array of Automattic domains
        $domain_whitelist = array('wordpress.com', 'wp.com');
        // Return $url if not an Automattic domain
        if (!in_array($domain, $domain_whitelist)) {
            return $url;
        }
        if (is_ssl()) {
            return preg_replace('|https?://[^/]++/|', 'https://s-ssl.wordpress.com/', $url);
        }
        srand(crc32(basename($url)));
        $static_counter = rand(0, 2);
        srand();
        // this resets everything that relies on this, like array_rand() and shuffle()
        return preg_replace('|://[^/]+?/|', "://s{$static_counter}.wp.com/", $url);
    }