lzssdecoder.cpp

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/***************************************************************************
 *   Copyright (C) 2005-2019 by the FIFE team                              *
 *   http://www.fifengine.net                                              *
 *   This file is part of FIFE.                                            *
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 *   FIFE is free software; you can redistribute it and/or                 *
 *   modify it under the terms of the GNU Lesser General Public            *
 *   License as published by the Free Software Foundation; either          *
 *   version 2.1 of the License, or (at your option) any later version.    *
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 *   This library 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     *
 *   Lesser General Public License for more details.                       *
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 *   Free Software Foundation, Inc.,                                       *
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// Standard C++ library includes
#include <algorithm>

// 3rd party library includes

// FIFE includes
#include "vfs/raw/rawdata.h"
#include "util/base/exception.h"

#include "lzssdecoder.h"

// just a quick&dirty wrapper around anchorites implementation - needs to be replaced with our own LZSS implementation
namespace FIFE {

    LZSSDecoder::LZSSDecoder() {}
    LZSSDecoder::~LZSSDecoder() {}


    void LZSSDecoder::decode(RawData* input, uint8_t* output, const uint32_t outputsize) {

        m_outindex = 0;
        m_outlen = outputsize;

        while (m_outindex < outputsize) {
            uint16_t blockdesc = input->read16Big();
            uint16_t bytesToRead = blockdesc & 0x7fff;

            if (blockdesc & 0x8000) { // uncompressed
                input->readInto(output + m_outindex, bytesToRead);
                m_outindex += bytesToRead;
            } else {
                // Allocate +2 bytes so that on corrupt data the LZSS
                // decoder won't crash the input buffer.
                std::vector<uint8_t> indata(bytesToRead + 2);
                input->readInto(&indata[0], bytesToRead);
                LZSSDecode(&indata[0], bytesToRead, output);
                // Note outindex is advanced inside LZSSDecode.
            }

        }
    }

    void LZSSDecoder::LZSSDecode(uint8_t* in , int64_t len, uint8_t* out) {
        const int64_t c_nRingBufferSize        = 4096;
        const int64_t c_nMatchLengthUpperLimit =   18;
        const int64_t c_nThreshold             =    2;

        char buffer[c_nRingBufferSize + c_nMatchLengthUpperLimit - 1];
        int32_t ibuf = 0;
        int32_t c;

        int32_t i;
        int32_t j;
        int32_t k;
        int32_t r;

        uint32_t flags;

        for (i = 0; i < c_nRingBufferSize - c_nMatchLengthUpperLimit; i++) {
            buffer[i] = ' ';
        }

        r = c_nRingBufferSize - c_nMatchLengthUpperLimit;
        flags = 0;
        while ( ibuf < len ) {
            if (((flags >>= 1) & 256) == 0) {
                c = in[ibuf++];
                flags = c | 0xff00;/* uses higher byte cleverly to count eight */
            }

            if (flags & 1) {
                c = in[ibuf++];
                out[m_outindex++] = c;

                buffer[r++] = c;
                r &= (c_nRingBufferSize - 1);
            } else {
                i = in[ibuf++];
                j = in[ibuf++];

                i |= ((j & 0xf0) << 4);
                j = (j & 0x0f) + c_nThreshold;

                for (k = 0; k <= j; k++) {
                    c = buffer[(i + k) & (c_nRingBufferSize - 1)];

                    out[m_outindex++] = c;

                    buffer[r++] = c;
                    r &= (c_nRingBufferSize - 1);
                }
            }
        }
    }


}