仿真平台内核初版 -tlib库 包含<sparc arm riscv powerPC>

lib/Packet.Net/PacketDotNet/Utils/ChecksumUtils.cs

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+/*
+This file is part of PacketDotNet.
+
+PacketDotNet is free software: you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+PacketDotNet 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 Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with PacketDotNet.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/*
+ * Copyright 2005 Tamir Gal <tamir@tamirgal.com>
+ * Copyright 2008-2009 Chris Morgan <chmorgan@gmail.com>
+ * Copyright 2008-2009 Phillip Lemon <lucidcomms@gmail.com>
+ */
+
+using System;
+using System.IO;
+
+namespace PacketDotNet.Utils
+{
+    /// <summary>
+    /// Computes the one's sum on a byte array.
+    /// Based TCP/IP Illustrated Vol. 2(1995) by Gary R. Wright and W. Richard
+    /// Stevens. Page 236. And on http://www.cs.utk.edu/~cs594np/unp/checksum.html
+    /// </summary>
+
+    /*
+    * taken from TCP/IP Illustrated Vol. 2(1995) by Gary R. Wright and W.
+    * Richard Stevens. Page 236
+    */
+    public sealed class ChecksumUtils
+    {
+        private ChecksumUtils() { }
+
+        /// <summary>
+        /// Computes the one's complement sum on a byte array
+        /// </summary>
+        public static int OnesComplementSum(byte[] bytes)
+        {
+            //just complement the one's sum
+            return OnesComplementSum(bytes, 0, bytes.Length);
+        }
+
+        /// <summary>
+        /// Computes the one's complement sum on a byte array
+        /// </summary>
+        public static int OnesComplementSum(byte[] bytes, int start, int len)
+        {
+            //just complement the one's sum
+            return (~OnesSum(bytes, start, len)) & 0xFFFF;
+        }
+
+        /// <summary>
+        /// Compute a ones sum of a byte array
+        /// </summary>
+        /// <param name="bytes">
+        /// A <see cref="System.Byte"/>
+        /// </param>
+        /// <returns>
+        /// A <see cref="System.Int32"/>
+        /// </returns>
+        public static int OnesSum(byte[] bytes)
+        {
+            return OnesSum(bytes, 0, bytes.Length);
+        }
+
+        /// <summary>
+        /// 16 bit sum of all values
+        /// http://en.wikipedia.org/wiki/Signed_number_representations#Ones.27_complement
+        /// </summary>
+        /// <param name="bytes">
+        /// A <see cref="System.Byte"/>
+        /// </param>
+        /// <param name="start">
+        /// A <see cref="System.Int32"/>
+        /// </param>
+        /// <param name="len">
+        /// A <see cref="System.Int32"/>
+        /// </param>
+        /// <returns>
+        /// A <see cref="System.Int32"/>
+        /// </returns>
+        public static int OnesSum(byte[] bytes, int start, int len)
+        {
+            MemoryStream memStream = new MemoryStream(bytes, start, len);
+            BinaryReader br = new BinaryReader(memStream);
+            Int32 sum = 0;
+
+            UInt16 val;
+
+            while (memStream.Position < memStream.Length -1)
+            {
+                val = (UInt16)System.Net.IPAddress.NetworkToHostOrder(br.ReadInt16());
+                sum += val;
+            }
+
+            // if we have a remaining byte we should add it
+            if (memStream.Position < len)
+            {
+                sum += br.ReadByte();
+            }
+
+            // fold the sum into 16 bits
+            while((sum >> 16) != 0)
+            {
+                sum = (sum & 0xffff) + (sum >> 16);
+            }
+
+            return sum;
+        }
+    }
+}