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unpack.h

/* 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 2
 * 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, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * $URL: https://scummvm.svn.sourceforge.net/svnroot/scummvm/scummvm/tags/release-1-1-1/engines/cine/unpack.h $
 * $Id: unpack.h 44802 2009-10-08 21:28:57Z fingolfin $
 *
 */

#ifndef CINE_UNPACK_H
#define CINE_UNPACK_H


#include "common/scummsys.h"

namespace Cine {

/**
 * A LZ77 style decompressor for Delphine's data files
 * used in at least Future Wars and Operation Stealth.
 * @note Works backwards in the source and destination buffers.
 * @warning Having the source and destination in the same buffer when unpacking can cause errors!
 */
00040 class CineUnpacker {
public:
      /**
       * Unpacks packed data from the source buffer to the destination buffer.
       * @note You may call this on already unpacked data but then source length must be equal to destination length.
       * @warning The source and destination should not point to the same buffer. If they do, errors may occur!
       * @param src Pointer to the source buffer.
       * @param srcLen Length of the source buffer.
       * @param dst Pointer to the destination buffer.
       * @param dstLen Length of the destination buffer.
       * @return True if no errors were detected in the source data and unpacking was successful, otherwise false.
       */
      bool unpack(const byte *src, uint srcLen, byte *dst, uint dstLen);
private:
      /**
       * Reads an unsigned big endian 32-bit integer from the source stream and goes backwards 4 bytes.
       * @return If the operation is valid, an unsigned big endian 32-bit integer read from the source stream.
       * @return If the operation is invalid, zero.
       * @note Sets internal error state if the read operation would be out of source bounds.
       */
      uint32 readSource();

      /**
       * Shifts the current internal 32-bit chunk to the right by one.
       * Puts input carry into internal chunk's topmost (i.e. leftmost) bit.
       * @return The least significant bit that was shifted out from the chunk.
       */
      uint rcr(bool inputCarry);

      /**
       * Get the next bit from the source stream.
       * @note Changes the bit position in the source stream.
       * @return The next bit from the source stream.
       */
      uint nextBit();

      /**
       * Get bits from the source stream.
       * @note Changes the bit position in the source stream.
       * @param numBits Number of bits to read from the source stream.
       * @return Integer value consisting of the bits read from the source stream (In range [0, (2 ** numBits) - 1]).
       * @return Later the bit was read from the source, the less significant it is in the return value.
       */
      uint getBits(uint numBits);

      /**
       * Copy raw bytes from the input stream and write them to the destination stream.
       * This is used when no adequately long match is found in the sliding window.
       * @note Sets internal error state if the operation would be out of bounds.
       * @param numBytes Amount of bytes to copy from the input stream
       */
      void unpackRawBytes(uint numBytes);

      /**
       * Copy bytes from the sliding window in the destination buffer.
       * This is used when a match of two bytes or longer is found.
       * @note Sets internal error state if the operation would be out of bounds.
       * @param offset Offset in the sliding window
       * @param numBytes Amount of bytes to copy
       */
      void copyRelocatedBytes(uint offset, uint numBytes);
private:
00102       uint32 _crc;      ///< Error-detecting code (This should be zero after successful unpacking)
00103       uint32 _chunk32b; ///< The current internal 32-bit chunk of source data
00104       byte *_dst;       ///< Pointer to the current position in the destination buffer
00105       const byte *_src; ///< Pointer to the current position in the source buffer

      // These are used for detecting errors (e.g. out of bounds issues) during unpacking
00108       bool _error;           ///< Did an error occur during unpacking?
00109       const byte *_srcBegin; ///< Source buffer's beginning
00110       const byte *_srcEnd;   ///< Source buffer's end
00111       byte *_dstBegin;       ///< Destination buffer's beginning
00112       byte *_dstEnd;         ///< Destination buffer's end
};

} // End of namespace Cine

#endif

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