gentoo-overlay/net-misc/mcproxy/files/fix_checksum_calculation.patch

From 93b5ace42268160ebbfff4c61818fb15fa2d9b99 Mon Sep 17 00:00:00 2001
From: Sebastian Woelke <Sebastian.Woelke@posteo.de>
Date: Thu, 24 Aug 2017 14:41:50 +0200
Subject: [PATCH] Fix checksum calculation

---
 mcproxy/src/utils/mroute_socket.cpp | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/mcproxy/src/utils/mroute_socket.cpp b/mcproxy/src/utils/mroute_socket.cpp
index 61289dd..3a55359 100644
--- a/src/utils/mroute_socket.cpp
+++ b/src/utils/mroute_socket.cpp
@@ -157,17 +157,23 @@ u_int16_t mroute_socket::calc_checksum(const unsigned char* buf, int buf_size) c
 
     u_int16_t* b = (u_int16_t*)buf;
     int sum = 0;
+    int csum;
 
     for (int i = 0; i < buf_size / 2; i++) {
-        ADD_SIGNED_NUM_U16(sum, b[i]);
-        //sum +=b[i];
+        sum +=b[i];
     }
 
     if (buf_size % 2 == 1) {
-        //sum += buf[buf_size-1];
-        ADD_SIGNED_NUM_U16(sum, buf[buf_size - 1]);
+        sum += buf[buf_size-1];
     }
 
+    // fold checksum 
+    csum = sum & 0xFFFF;
+    sum = sum >> 16;
+    sum += csum;
+    // fold again in case of overflow.
+    sum += sum >> 16;
+
     return ~sum;
 }