--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/internet-stack/ipv4-checksum.cc	Mon Jun 09 15:40:22 2008 -0700
@@ -0,0 +1,52 @@
+/* -*-  Mode: C++; c-file-style: "gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2005,2006,2007 INRIA
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
+ */
+#include "ipv4-checksum.h"
+
+namespace ns3 {
+
+uint16_t 
+Ipv4ChecksumCalculate (uint16_t checksum, uint8_t *buffer, uint16_t size)
+{
+  /* see RFC 1071 to understand this code. */
+  uint32_t sum = checksum;
+  uint16_t *data = (uint16_t *) buffer;
+  for (uint16_t i = 0; i < (size/2); i++) {
+    sum += data[i];
+  }
+  if ((size % 2) != 0) {
+    uint8_t tmpBuf[2];
+    tmpBuf[0] = buffer[size-1];
+    tmpBuf[1] = 0;
+    data = (uint16_t *)tmpBuf;
+    sum += *data;
+  }
+  while (sum >> 16) {
+    sum = (sum & 0xffff) + (sum >> 16);
+  }
+  return sum;
+}
+
+uint16_t 
+Ipv4ChecksumComplete (uint16_t checksum)
+{
+  return ~checksum;
+}
+
+}; //namespace ns3