GARbro-mirror/ArcFormats/Crc32.cs

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//! \file Crc32.cs
//! \date Fri Aug 19 09:18:42 2016
//! \brief Crc32 with normal polynomial representation.
//
// Copyright (C) 2016 by morkt
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to
// deal in the Software without restriction, including without limitation the
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
// sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
// IN THE SOFTWARE.
//
namespace GameRes.Utility
{
/// <summary>
/// Crc32 with normal polynomial representation.
/// </summary>
public sealed class Crc32Normal : ICheckSum
{
private static readonly uint[] crc_table = InitializeTable();
public static uint[] Table { get { return crc_table; } }
private static uint[] InitializeTable ()
{
const uint polynomial = 0x04C11DB7;
var table = new uint[256];
for (uint n = 0; n < 256; n++)
{
uint c = n << 24;
for (int k = 0; k < 8; k++)
{
if (0 != (c & 0x80000000u))
c = polynomial ^ (c << 1);
else
c <<= 1;
}
table[n] = c;
}
return table;
}
public static uint UpdateCrc (uint init_crc, byte[] data, int pos, int length)
{
uint c = init_crc;
for (int n = 0; n < length; n++)
c = crc_table[(c >> 24) ^ data[pos+n]] ^ (c << 8);
return c;
}
public static uint Compute (byte[] buf, int pos, int len)
{
return ~UpdateCrc (0xffffffff, buf, pos, len);
}
private uint m_crc = 0xffffffff;
public uint Value { get { return ~m_crc; } }
public void Update (byte[] buf, int pos, int len)
{
m_crc = UpdateCrc (m_crc, buf, pos, len);
}
}
}