From 2ab42e81ff959e31d846e6b2f7dc33fa9414042b Mon Sep 17 00:00:00 2001
From: Neale Pickett <neale@lanl.gov>
Date: Wed, 30 Jan 2013 15:08:04 -0700
Subject: [PATCH] fix IP checksum routine, finally

---
 ip.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/ip.py b/ip.py
index e4832a1..02acd1e 100644
--- a/ip.py
+++ b/ip.py
@@ -213,9 +213,9 @@ class TCP_Recreate:
                             0,      # Header checksum
                             sip,
                             dip)
-        shorts = struct.unpack('!hhhhhhhhhh', iphdr)
+        shorts = struct.unpack('!HHHHHHHHHH', iphdr)
         shsum = sum(shorts)
-        ipsum = struct.pack('!h', (~shsum & 0xffff) - 2) # -2? WTF?
+        ipsum = struct.pack('!H', ((shsum + (shsum >> 16)) & 0xffff) ^ 0xffff)
         iphdr = iphdr[:10] + ipsum + iphdr[12:]
 
         tcphdr = struct.pack('!HHLLBBHHH',