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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;
}
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