From a3f979febf0a3ff63feea95a47cae71e35da3c84 Mon Sep 17 00:00:00 2001
From: Piotr Jurkiewicz <piotr.jerzy.jurkiewicz@gmail.com>
Date: Tue, 19 Nov 2013 06:36:55 -0800
Subject: [PATCH] bug 1776: improve Csma CRC performance

---
 src/csma/model/csma-net-device.cc     |  1 -
 src/network/utils/ethernet-trailer.cc | 25 +++----------------------
 src/network/utils/ethernet-trailer.h  |  2 --
 src/network/wscript                   |  2 ++
 4 files changed, 5 insertions(+), 25 deletions(-)

diff --git a/src/csma/model/csma-net-device.cc b/src/csma/model/csma-net-device.cc
index 5a4bcc93c..f98d0686e 100644
--- a/src/csma/model/csma-net-device.cc
+++ b/src/csma/model/csma-net-device.cc
@@ -700,7 +700,6 @@ CsmaNetDevice::Receive (Ptr<Packet> packet, Ptr<CsmaNetDevice> senderDevice)
       trailer.EnableFcs (true);
     }
 
-  trailer.CheckFcs (packet);
   bool crcGood = trailer.CheckFcs (packet);
   if (!crcGood)
     {
diff --git a/src/network/utils/ethernet-trailer.cc b/src/network/utils/ethernet-trailer.cc
index df769f832..ed5e50e66 100644
--- a/src/network/utils/ethernet-trailer.cc
+++ b/src/network/utils/ethernet-trailer.cc
@@ -22,6 +22,7 @@
 #include "ns3/log.h"
 #include "ns3/trailer.h"
 #include "ethernet-trailer.h"
+#include "crc32.h"
 
 NS_LOG_COMPONENT_DEFINE ("EthernetTrailer");
 
@@ -59,7 +60,7 @@ EthernetTrailer::CheckFcs (Ptr<const Packet> p) const
 
   buffer = new uint8_t[len];
   p->CopyData (buffer, len);
-  crc = DoCalcFcs (buffer, len);
+  crc = CRC32Calculate (buffer, len);
   delete[] buffer;
   return (m_fcs == crc);
 }
@@ -78,7 +79,7 @@ EthernetTrailer::CalcFcs (Ptr<const Packet> p)
 
   buffer = new uint8_t[len];
   p->CopyData (buffer, len);
-  m_fcs = DoCalcFcs (buffer, len);
+  m_fcs = CRC32Calculate (buffer, len);
   delete[] buffer;
 }
 
@@ -152,24 +153,4 @@ EthernetTrailer::Deserialize (Buffer::Iterator end)
   return size;
 }
 
-// This code is copied from /lib/crc32.c in the linux kernel.
-// It assumes little endian ordering.
-uint32_t
-EthernetTrailer::DoCalcFcs (uint8_t const *buffer, size_t len) const
-{
-  NS_LOG_FUNCTION (this << &buffer << len);
-  uint32_t crc = 0xffffffff;
-  int i;
-
-  while (len--)
-    {
-      crc ^= *buffer++;
-      for (i = 0; i < 8; i++)
-        {
-          crc = (crc >> 1) ^ ((crc & 1) ? 0xedb88320 : 0);
-        }
-    }
-  return ~crc;
-}
-
 } // namespace ns3
diff --git a/src/network/utils/ethernet-trailer.h b/src/network/utils/ethernet-trailer.h
index c7de33fc5..f523744e9 100644
--- a/src/network/utils/ethernet-trailer.h
+++ b/src/network/utils/ethernet-trailer.h
@@ -104,8 +104,6 @@ private:
   bool m_calcFcs;
   uint32_t m_fcs; /// Value of the fcs contained in the trailer
 
-  uint32_t DoCalcFcs (uint8_t const *buffer, size_t len) const;
-
 };
 
 } // namespace ns3
diff --git a/src/network/wscript b/src/network/wscript
index 850aab833..2d96f8853 100644
--- a/src/network/wscript
+++ b/src/network/wscript
@@ -25,6 +25,7 @@ def build(bld):
         'model/trailer.cc',
         'utils/address-utils.cc',
         'utils/ascii-file.cc',
+        'utils/crc32.cc',
         'utils/data-rate.cc',
         'utils/drop-tail-queue.cc',
         'utils/error-model.cc',
@@ -102,6 +103,7 @@ def build(bld):
         'utils/address-utils.h',
         'utils/ascii-file.h',
         'utils/ascii-test.h',
+        'utils/crc32.h',
         'utils/data-rate.h',
         'utils/drop-tail-queue.h',
         'utils/error-model.h',