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357249fb5a
They have almost nothing in common. And we probably want to kill slow implementation anyway now that we have tests
174 lines
4.5 KiB
C++
174 lines
4.5 KiB
C++
/* ScummVM - Graphic Adventure Engine
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*
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* ScummVM is the legal property of its developers, whose names
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* are too numerous to list here. Please refer to the COPYRIGHT
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* file distributed with this source distribution.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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/**********************************************************************
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*
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* Filename: crc.c
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*
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* Description: Slow implementation of the CRC standards.
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*
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* Notes:
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*
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*
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* Copyright (c) 2000 by Michael Barr. This software is placed into
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* the public domain and may be used for any purpose. However, this
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* notice must not be changed or removed and no warranty is either
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* expressed or implied by its publication or distribution.
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**********************************************************************/
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#ifndef COMMON_CRC_SLOW_H
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#define COMMON_CRC_SLOW_H
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#include "common/system.h" // For types.
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namespace Common {
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template <typename T>
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class CRCSlow {
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public:
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CRCSlow(T poly, T init_remainder, T final_xor, bool need_reflect);
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T crcSlow(byte const message[], int nBytes) const;
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protected:
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const T _poly;
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const T _init_remainder;
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const T _final_xor;
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const int _width;
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const int _topbit;
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const bool _reflect;
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template<typename R>
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static R reflect(R data);
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byte reflectData(byte x) const { return _reflect ? reflect<byte>(x) : x; }
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T reflectRemainder(T x) const { return _reflect ? reflect<T>(x) : x; }
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};
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/*********************************************************************
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*
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* Function: reflect()
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*
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* Description: Reorder the bits of a binary sequence, by reflecting
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* them about the middle position.
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*
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* Notes: No checking is done that nBits <= 32.
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*
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* Returns: The reflection of the original data.
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*
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*********************************************************************/
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template<typename T> template<typename R>
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R CRCSlow<T>::reflect(R data) {
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R reflection = 0;
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/*
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* Reflect the data about the center bit.
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*/
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for (byte bit = 0; bit < sizeof(R) * 8; ++bit) {
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/*
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* If the LSB bit is set, set the reflection of it.
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*/
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if (data & 0x01) {
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reflection |= (1 << ((sizeof(R) * 8 - 1) - bit));
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}
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data = (data >> 1);
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}
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return reflection;
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}
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/*********************************************************************
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*
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* Function: crcSlow()
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*
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* Description: Compute the CRC of a given message.
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*
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* Notes:
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*
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* Returns: The CRC of the message.
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*
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*********************************************************************/
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template<typename T>
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T CRCSlow<T>::crcSlow(byte const message[], int nBytes) const {
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T remainder = _init_remainder;
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/*
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* Perform modulo-2 division, a byte at a time.
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*/
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for (int b = 0; b < nBytes; ++b) {
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/*
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* Bring the next byte into the remainder.
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*/
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remainder ^= reflectData(message[b]) << (_width - 8);
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/*
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* Perform modulo-2 division, a bit at a time.
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*/
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for (byte bit = 8; bit > 0; --bit) {
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/*
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* Try to divide the current data bit.
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*/
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if (remainder & _topbit) {
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remainder = (remainder << 1) ^ _poly;
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} else {
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remainder = (remainder << 1);
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}
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}
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}
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/*
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* The final remainder is the CRC result.
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*/
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return reflectRemainder(remainder) ^ _final_xor;
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}
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template<typename T>
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CRCSlow<T>::CRCSlow(T poly, T init_remainder, T final_xor, bool need_reflect) :
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_poly(poly), _init_remainder(init_remainder), _final_xor(final_xor), _width(8 * sizeof(T)), _topbit(1 << (8 * sizeof(T) - 1)), _reflect(need_reflect) {}
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class CRC_CCITT_Slow : public CRCSlow<uint16> {
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public:
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CRC_CCITT_Slow() : CRCSlow<uint16>(0x1021, 0xFFFF, 0x0000, false) {}
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};
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class CRC_BINHEX_Slow : public CRCSlow<uint16> {
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public:
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CRC_BINHEX_Slow() : CRCSlow<uint16>(0x1021, 0x0000, 0x0000, false) {}
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};
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class CRC16_Slow : public CRCSlow<uint16> {
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public:
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CRC16_Slow() : CRCSlow<uint16>(0x8005, 0x0000, 0x0000, true) {}
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};
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class CRC32_Slow : public CRCSlow<uint32> {
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public:
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CRC32_Slow() : CRCSlow<uint32>(0x04C11DB7, 0xFFFFFFFF, 0xFFFFFFFF, true) {}
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};
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} // End of namespace Common
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#endif
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