140 lines
4.8 KiB
C#
140 lines
4.8 KiB
C#
/*
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* Copyright (c) Contributors, http://opensimulator.org/
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* See CONTRIBUTORS.TXT for a full list of copyright holders.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* * Neither the name of the OpenSimulator Project nor the
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* names of its contributors may be used to endorse or promote products
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* derived from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
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* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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using System;
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using System.Security.Cryptography;
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namespace OpenSim.Framework
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{
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// this is more generic than openmetaverse CRC32
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public class Crc32 : HashAlgorithm
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{
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public const UInt32 DefaultPolynomial = 0xedb88320;
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public const UInt32 DefaultSeed = 0xffffffff;
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private UInt32 hash;
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private UInt32 seed;
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private UInt32[] table;
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private static UInt32[] defaultTable;
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public Crc32()
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{
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table = InitializeTable(DefaultPolynomial);
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seed = DefaultSeed;
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Initialize();
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}
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public Crc32(UInt32 polynomial, UInt32 seed)
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{
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table = InitializeTable(polynomial);
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this.seed = seed;
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Initialize();
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}
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public override void Initialize()
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{
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hash = seed;
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}
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protected override void HashCore(byte[] buffer, int start, int length)
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{
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hash = CalculateHash(table, hash, buffer, start, length);
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}
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protected override byte[] HashFinal()
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{
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byte[] hashBuffer = UInt32ToBigEndianBytes(~hash);
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this.HashValue = hashBuffer;
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return hashBuffer;
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}
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public override int HashSize
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{
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get { return 32; }
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}
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public static UInt32 Compute(byte[] buffer)
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{
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return ~CalculateHash(InitializeTable(DefaultPolynomial), DefaultSeed, buffer, 0, buffer.Length);
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}
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public static UInt32 Compute(UInt32 seed, byte[] buffer)
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{
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return ~CalculateHash(InitializeTable(DefaultPolynomial), seed, buffer, 0, buffer.Length);
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}
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public static UInt32 Compute(UInt32 polynomial, UInt32 seed, byte[] buffer)
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{
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return ~CalculateHash(InitializeTable(polynomial), seed, buffer, 0, buffer.Length);
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}
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private static UInt32[] InitializeTable(UInt32 polynomial)
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{
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if (polynomial == DefaultPolynomial && defaultTable != null)
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return defaultTable;
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UInt32[] createTable = new UInt32[256];
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for (int i = 0; i < 256; i++)
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{
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UInt32 entry = (UInt32)i;
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for (int j = 0; j < 8; j++)
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if ((entry & 1) == 1)
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entry = (entry >> 1) ^ polynomial;
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else
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entry = entry >> 1;
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createTable[i] = entry;
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}
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if (polynomial == DefaultPolynomial)
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defaultTable = createTable;
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return createTable;
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}
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private static UInt32 CalculateHash(UInt32[] table, UInt32 seed, byte[] buffer, int start, int size)
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{
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UInt32 crc = seed;
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for (int i = start; i < size; i++)
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unchecked
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{
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crc = (crc >> 8) ^ table[buffer[i] ^ crc & 0xff];
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}
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return crc;
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}
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private byte[] UInt32ToBigEndianBytes(UInt32 x)
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{
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return new byte[] {
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(byte)((x >> 24) & 0xff),
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(byte)((x >> 16) & 0xff),
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(byte)((x >> 8) & 0xff),
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(byte)(x & 0xff) };
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}
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}
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}
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