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