From 4aa6a13c1de98667a208e6d3b733558b0c4345d5 Mon Sep 17 00:00:00 2001
From: Eric Vyncke <eric@vyncke.org>
Date: Tue, 30 Jan 2024 20:56:19 +0900
Subject: [PATCH] Add commonPrefixLength()

Compute the length of the longest prefix match.
---
 lib/ipaddr.js | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/lib/ipaddr.js b/lib/ipaddr.js
index d203f0e..5912a53 100644
--- a/lib/ipaddr.js
+++ b/lib/ipaddr.js
@@ -129,6 +129,30 @@
         return true;
     }
 
+    function matchLength(first, second) {
+        if (first.length !== second.length) {
+            throw new Error('ipaddr: cannot matchLength for objects with different lengths');
+        }
+	let offset = 0 ;
+	let length = 0 ;
+	while (offset < first.length && first[offset] == second[offset]) {
+		offset++ ;
+		length += 8 ;
+	}
+	let bit = 0x80 ;
+	let index = 0 ;
+	if (offset < first.length) {
+		let a = first[offset] ;
+		let b = second[offset] ;
+		while (index < 8 && (a & bit) == (b & bit)) {
+			index ++ ;
+			bit = bit >> 1 ;
+		}
+		return length + index ;
+	} else
+	    return length ;
+    }
+
     function parseIntAuto (string) {
         // Hexadedimal base 16 (0x#)
         if (hexRegex.test(string)) {
@@ -240,6 +264,15 @@
             return matchCIDR(this.octets, other.octets, 8, cidrRange);
         };
 
+	IPv4.prototype.commonPrefixLength = function (other) {
+            if (other.kind() !== 'ipv4') {
+                throw new Error('ipaddr: cannot match ipv6 address with non-ipv6 one');
+            }
+
+	    return matchLength(this.toByteArray(), other.toByteArray()) ;
+	}
+
+
         // returns a number of leading ones in IPv4 address, making sure that
         // the rest is a solid sequence of 0's (valid netmask)
         // returns either the CIDR length or null if mask is not valid
@@ -602,6 +635,14 @@
             return matchCIDR(this.parts, other.parts, 16, cidrRange);
         };
 
+	IPv6.prototype.commonPrefixLength = function (other) {
+            if (other.kind() !== 'ipv6') {
+                throw new Error('ipaddr: cannot match ipv6 address with non-ipv6 one');
+            }
+
+	    return matchLength(this.toByteArray(), other.toByteArray()) ;
+	}
+
         // returns a number of leading ones in IPv6 address, making sure that
         // the rest is a solid sequence of 0's (valid netmask)
         // returns either the CIDR length or null if mask is not valid