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delphine-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-0-11-1/engines/cruise/delphine-unpack.cpp $
 * $Id: delphine-unpack.cpp 30944 2008-02-23 22:50:18Z sev $
 *
 */


#include "common/endian.h"

namespace Cruise {

struct UnpackCtx {
      int size, datasize;
      uint32 crc;
      uint32 chk;
      byte *dst;
      const byte *src;
};

static int rcr(UnpackCtx *uc, int CF) {
      int rCF = (uc->chk & 1);
      uc->chk >>= 1;
      if (CF) {
            uc->chk |= 0x80000000;
      }
      return rCF;
}

static int nextChunk(UnpackCtx *uc) {
      int CF = rcr(uc, 0);
      if (uc->chk == 0) {
            uc->chk = READ_BE_UINT32(uc->src); uc->src -= 4;
            uc->crc ^= uc->chk;
            CF = rcr(uc, 1);
      }
      return CF;
}

static uint16 getCode(UnpackCtx *uc, byte numChunks) {
      uint16 c = 0;
      while (numChunks--) {
            c <<= 1;
            if (nextChunk(uc)) {
                  c |= 1;
            }
      }
      return c;
}

static void unpackHelper1(UnpackCtx *uc, byte numChunks, byte addCount) {
      uint16 count = getCode(uc, numChunks) + addCount + 1;
      uc->datasize -= count;
      while (count--) {
            *uc->dst = (byte)getCode(uc, 8);
            --uc->dst;
      }
}

static void unpackHelper2(UnpackCtx *uc, byte numChunks) {
      uint16 i = getCode(uc, numChunks);
      uint16 count = uc->size + 1;
      uc->datasize -= count;
      while (count--) {
            *uc->dst = *(uc->dst + i);
            --uc->dst;
      }
}

bool delphineUnpack(byte *dst, const byte *src, int len) {
      UnpackCtx uc;
      uc.src = src + len - 4;
      uc.datasize = READ_BE_UINT32(uc.src); uc.src -= 4;
      uc.dst = dst + uc.datasize - 1;
      uc.size = 0;
      uc.crc = READ_BE_UINT32(uc.src); uc.src -= 4;
      uc.chk = READ_BE_UINT32(uc.src); uc.src -= 4;
      uc.crc ^= uc.chk;
      do {
            if (!nextChunk(&uc)) {
                  uc.size = 1;
                  if (!nextChunk(&uc)) {
                        unpackHelper1(&uc, 3, 0);
                  } else {
                        unpackHelper2(&uc, 8);
                  }
            } else {
                  uint16 c = getCode(&uc, 2);
                  if (c == 3) {
                        unpackHelper1(&uc, 8, 8);
                  } else if (c < 2) {
                        uc.size = c + 2;
                        unpackHelper2(&uc, c + 9);
                  } else {
                        uc.size = getCode(&uc, 8);
                        unpackHelper2(&uc, 12);
                  }
            }
      } while (uc.datasize > 0);
      return uc.crc == 0;
}

} // End of namespace Cruise

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