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/* ScummVM - Graphic Adventure Engine
*
* ScummVM is the legal property of its developers, whose names
* are too numerous to list here. Please refer to the COPYRIGHT
* file distributed with this source distribution.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
/**********************************************************************
*
* Filename: crc.c
*
* Description: Slow implementation of the CRC standards.
*
* Notes:
*
*
* Copyright (c) 2000 by Michael Barr. This software is placed into
* the public domain and may be used for any purpose. However, this
* notice must not be changed or removed and no warranty is either
* expressed or implied by its publication or distribution.
**********************************************************************/
#ifndef COMMON_CRC_SLOW_H
#define COMMON_CRC_SLOW_H
#include "common/system.h" // For types.
namespace Common {
template <typename T>
class CRCSlow {
public:
CRCSlow(T poly, T init_remainder, T final_xor, bool need_reflect);
T crcSlow(byte const message[], int nBytes) const;
protected:
const T _poly;
const T _init_remainder;
const T _final_xor;
const int _width;
const int _topbit;
const bool _reflect;
template<typename R>
static R reflect(R data);
byte reflectData(byte x) const { return _reflect ? reflect<byte>(x) : x; }
T reflectRemainder(T x) const { return _reflect ? reflect<T>(x) : x; }
};
/*********************************************************************
*
* Function: reflect()
*
* Description: Reorder the bits of a binary sequence, by reflecting
* them about the middle position.
*
* Notes: No checking is done that nBits <= 32.
*
* Returns: The reflection of the original data.
*
*********************************************************************/
template<typename T> template<typename R>
R CRCSlow<T>::reflect(R data) {
R reflection = 0;
/*
* Reflect the data about the center bit.
*/
for (byte bit = 0; bit < sizeof(R) * 8; ++bit) {
/*
* If the LSB bit is set, set the reflection of it.
*/
if (data & 0x01) {
reflection |= (1 << ((sizeof(R) * 8 - 1) - bit));
}
data = (data >> 1);
}
return reflection;
}
/*********************************************************************
*
* Function: crcSlow()
*
* Description: Compute the CRC of a given message.
*
* Notes:
*
* Returns: The CRC of the message.
*
*********************************************************************/
template<typename T>
T CRCSlow<T>::crcSlow(byte const message[], int nBytes) const {
T remainder = _init_remainder;
/*
* Perform modulo-2 division, a byte at a time.
*/
for (int b = 0; b < nBytes; ++b) {
/*
* Bring the next byte into the remainder.
*/
remainder ^= reflectData(message[b]) << (_width - 8);
/*
* Perform modulo-2 division, a bit at a time.
*/
for (byte bit = 8; bit > 0; --bit) {
/*
* Try to divide the current data bit.
*/
if (remainder & _topbit) {
remainder = (remainder << 1) ^ _poly;
} else {
remainder = (remainder << 1);
}
}
}
/*
* The final remainder is the CRC result.
*/
return reflectRemainder(remainder) ^ _final_xor;
}
template<typename T>
CRCSlow<T>::CRCSlow(T poly, T init_remainder, T final_xor, bool need_reflect) :
_poly(poly), _init_remainder(init_remainder), _final_xor(final_xor), _width(8 * sizeof(T)), _topbit(1 << (8 * sizeof(T) - 1)), _reflect(need_reflect) {}
class CRC_CCITT_Slow : public CRCSlow<uint16> {
public:
CRC_CCITT_Slow() : CRCSlow<uint16>(0x1021, 0xFFFF, 0x0000, false) {}
};
class CRC_BINHEX_Slow : public CRCSlow<uint16> {
public:
CRC_BINHEX_Slow() : CRCSlow<uint16>(0x1021, 0x0000, 0x0000, false) {}
};
class CRC16_Slow : public CRCSlow<uint16> {
public:
CRC16_Slow() : CRCSlow<uint16>(0x8005, 0x0000, 0x0000, true) {}
};
class CRC32_Slow : public CRCSlow<uint32> {
public:
CRC32_Slow() : CRCSlow<uint32>(0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, true) {}
};
} // End of namespace Common
#endif
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