scummvm/engines/prince/decompress.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.
 *
 */

// John_Doe's implementation

#include "prince/decompress.h"

namespace Prince {

static const uint16 table1[] = {
    0x8000, 0x0002,
    0x4000, 0x0004,
    0x2000, 0x0008,
    0x1000, 0x0010,
    0x0800, 0x0020,
    0x0400, 0x0040,
    0x0200, 0x0080,
    0x0100, 0x0100,
    0x0080, 0x0200,
    0x0040, 0x0400
};

static const uint32 table2[] = {
    0x0000F000,
    0x0020FC00,
    0x00A0FF00,
    0x02A0FF80,
    0x06A0FFC0,
    0x0EA0FFE0,
    0x1EA0FFF0,
    0x3EA0FFF8
};

static const uint16 table3[] = {
    0x8000, 0x0000,
    0x4000, 0x0002,
    0x2000, 0x0006,
    0x1000, 0x000E,
    0x0800, 0x001E,
    0x0400, 0x003E,
    0x0200, 0x007E,
    0x0100, 0x00FE,
    0x0080, 0x01FE,
    0x0040, 0x03FE,
    0x0020, 0x07FE,
    0x0010, 0x0FFE,
    0x0008, 0x1FFE,
    0x0004, 0x3FFE,
    0x0002, 0x7FFE,
    0x0001, 0xFFFE
};

void Decompressor::decompress(byte *source, byte *dest, uint32 destSize) {
    byte *destEnd = dest + destSize;
    int more;
    _src = source;
    _dst = dest;
    _bitBuffer = 0x80;
    while (_dst < destEnd) {
        uint32 ebp;
        uint16 offset, length;
        if (getBit()) {
            if (getBit()) {
                if (getBit()) {
                    if (getBit()) {
                        if (getBit()) {
                            if (getBit()) {
                                uint32 tableIndex = 0;
                                while (getBit())
                                    tableIndex++;
                                length = table3[tableIndex * 2 + 0];
                                do {
                                    more = !(length & 0x8000);
                                    length = (length << 1) | getBit();
                                } while (more);
                                length += table3[tableIndex * 2 + 1];
                                length++;
                                memcpy(_dst, _src, length);
                                _src += length;
                                _dst += length;
                            }
                            *_dst++ = *_src++;
                        }
                        *_dst++ = *_src++;
                    }
                    *_dst++ = *_src++;
                }
                *_dst++ = *_src++;
            }
            *_dst++ = *_src++;
        }
        if (!getBit()) {
            if (getBit()) {
                uint32 tableIndex = getBit();
                tableIndex = (tableIndex << 1) | getBit();
                tableIndex = (tableIndex << 1) | getBit();
                ebp = table2[tableIndex];
                length = 1;
            } else {
                ebp = 0x0000FF00;
                length = 0;
            }
        } else {
            uint32 tableIndex = 0;
            while (getBit())
                tableIndex++;
            length = table1[tableIndex * 2 + 0];
            do {
                more = !(length & 0x8000);
                length = (length << 1) | getBit();
            } while (more);
            length += table1[tableIndex * 2 + 1];
            tableIndex = getBit();
            tableIndex = (tableIndex << 1) | getBit();
            tableIndex = (tableIndex << 1) | getBit();
            ebp = table2[tableIndex];
        }
        offset = ebp & 0xFFFF;
        do {
            if (_bitBuffer == 0x80) {
                if (offset >= 0xFF00) {
                    offset = (offset << 8) | *_src++;
                }
            }
            more = offset & 0x8000;
            offset = (offset << 1) | getBit();
        } while (more);
        offset += (ebp >> 16);
        length += 2;
        while (length--) {
            if (_dst >= destEnd) {
                return;
            }
            *_dst = *(_dst - offset);
            _dst++;
        }
    }
}

int Decompressor::getBit() {
    int bit = (_bitBuffer & 0x80) >> 7;
    _bitBuffer <<= 1;
    if (_bitBuffer == 0) {
        _bitBuffer = *_src++;
        bit = (_bitBuffer & 0x80) >> 7;
        _bitBuffer <<= 1;
        _bitBuffer |= 1;
    }
    return bit;
}

} // End of namespace Prince