From 6e9af3bb2973cf34e6d5fa2fb86420e2a9ce95af Mon Sep 17 00:00:00 2001
From: Tyler Cosgrove <Vivalldi@users.noreply.github.com>
Date: Sat, 20 Apr 2019 04:29:19 +1200
Subject: [PATCH] Add getSubnet util to Grav\Common\Utils (#2465)

---
 system/src/Grav/Common/Utils.php | 40 ++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/system/src/Grav/Common/Utils.php b/system/src/Grav/Common/Utils.php
index 42f1fbe69..c254009e5 100644
--- a/system/src/Grav/Common/Utils.php
+++ b/system/src/Grav/Common/Utils.php
@@ -1469,4 +1469,44 @@ abstract class Utils
 
         return $string;
     }
+
+    /**
+     * Find the subnet of an ip with CIDR prefix size
+     *
+     * @param string $ip
+     * @param int $prefix
+     *
+     * @return string
+     * @throws \InvalidArgumentException if provided an invalid IP
+     */
+    public static function getSubnet($ip, $prefix = 64)
+    {
+        if (!filter_var($ip, FILTER_VALIDATE_IP)) {
+            throw new \InvalidArgumentException('Invalid IP: ' . $ip);
+        }
+
+        // Packed representation of IP
+        $ip = inet_pton($ip);
+
+        // Maximum netmask length = same as packed address
+        $len = 8*strlen($ip);
+        if ($prefix > $len) $prefix = $len;
+
+        $mask  = str_repeat('f', $prefix>>2);
+
+        switch($prefix & 3)
+        {
+            case 3: $mask .= 'e'; break;
+            case 2: $mask .= 'c'; break;
+            case 1: $mask .= '8'; break;
+        }
+        $mask = str_pad($mask, $len>>2, '0');
+
+        // Packed representation of netmask
+        $mask = pack('H*', $mask);
+        // Bitwise - Take all bits that are both 1 to generate subnet
+        $subnet = inet_ntop($ip & $mask);
+
+        return $subnet;
+    }
 }