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unpack.cpp

/* 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-0-13-1/engines/cine/unpack.cpp $
 * $Id: unpack.cpp 34034 2008-08-19 11:55:20Z buddha_ $
 *
 */


#include "common/endian.h"

#include "cine/unpack.h"

namespace Cine {

00033 uint32 CineUnpacker::readSource() {
      if (_src < _srcBegin || _src + 4 > _srcEnd) {
            _error = true;
            return 0; // The source pointer is out of bounds, returning a default value
      }
      uint32 value = READ_BE_UINT32(_src);
      _src -= 4;
      return value;
}

00043 uint CineUnpacker::rcr(bool inputCarry) {
      uint outputCarry = (_chunk32b & 1);
      _chunk32b >>= 1;
      if (inputCarry) {
            _chunk32b |= 0x80000000;
      }
      return outputCarry;
}

00052 uint CineUnpacker::nextBit() {
      uint carry = rcr(false);
      // Normally if the chunk becomes zero then the carry is one as
      // the end of chunk marker is always the last to be shifted out.
      if (_chunk32b == 0) {
            _chunk32b = readSource();
            _crc ^= _chunk32b;
            carry = rcr(true); // Put the end of chunk marker in the most significant bit
      }
      return carry;
}

00064 uint CineUnpacker::getBits(uint numBits) {
      uint c = 0;
      while (numBits--) {
            c <<= 1;
            c |= nextBit();
      }
      return c;
}

00073 void CineUnpacker::unpackRawBytes(uint numBytes) {
      if (_dst >= _dstEnd || _dst - numBytes + 1 < _dstBegin) {
            _error = true;
            return; // Destination pointer is out of bounds for this operation
      }
      while (numBytes--) {
            *_dst = (byte)getBits(8);
            --_dst;
      }
}

00084 void CineUnpacker::copyRelocatedBytes(uint offset, uint numBytes) {
      if (_dst + offset >= _dstEnd || _dst - numBytes + 1 < _dstBegin) {
            _error = true;
            return; // Destination pointer is out of bounds for this operation
      }
      while (numBytes--) {
            *_dst = *(_dst + offset);
            --_dst;
      }
}

00095 bool CineUnpacker::unpack(const byte *src, uint srcLen, byte *dst, uint dstLen) {
      // Initialize variables used for detecting errors during unpacking
      _error    = false;
      _srcBegin = src;
      _srcEnd   = src + srcLen;
      _dstBegin = dst;
      _dstEnd   = dst + dstLen;

      // Handle already unpacked data here
      if (srcLen == dstLen) {
            // Source length is same as destination length so the source
            // data is already unpacked. Let's just copy it then.
            memcpy(dst, src, srcLen);
            return true;
      }

      // Initialize other variables
      _src = _srcBegin + srcLen - 4;
      uint32 unpackedLength = readSource(); // Unpacked length in bytes
      _dst = _dstBegin + unpackedLength - 1;
      _crc = readSource();
      _chunk32b = readSource();
      _crc ^= _chunk32b;

      while (_dst >= _dstBegin && !_error) {
            /*
            Bits  => Action:
            0 0   => unpackRawBytes(3 bits + 1)              i.e. unpackRawBytes(1..8)
            1 1 1 => unpackRawBytes(8 bits + 9)              i.e. unpackRawBytes(9..264)
            0 1   => copyRelocatedBytes(8 bits, 2)           i.e. copyRelocatedBytes(0..255, 2)
            1 0 0 => copyRelocatedBytes(9 bits, 3)           i.e. copyRelocatedBytes(0..511, 3)
            1 0 1 => copyRelocatedBytes(10 bits, 4)          i.e. copyRelocatedBytes(0..1023, 4)
            1 1 0 => copyRelocatedBytes(12 bits, 8 bits + 1) i.e. copyRelocatedBytes(0..4095, 1..256)
            */
            if (!nextBit()) { // 0...
                  if (!nextBit()) { // 0 0
                        uint numBytes = getBits(3) + 1;
                        unpackRawBytes(numBytes);
                  } else { // 0 1
                        uint numBytes = 2;
                        uint offset   = getBits(8);
                        copyRelocatedBytes(offset, numBytes);
                  }
            } else { // 1...
                  uint c = getBits(2);
                  if (c == 3) { // 1 1 1
                        uint numBytes = getBits(8) + 9;
                        unpackRawBytes(numBytes);
                  } else if (c < 2) { // 1 0 x
                        uint numBytes = c + 3;
                        uint offset   = getBits(c + 9);
                        copyRelocatedBytes(offset, numBytes);
                  } else { // 1 1 0
                        uint numBytes = getBits(8) + 1;
                        uint offset   = getBits(12);
                        copyRelocatedBytes(offset, numBytes);
                  }
            }
      }
      return !_error && (_crc == 0);
}

} // End of namespace Cine

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