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/* 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.
 *
 */

#include "sherlock/decompress.h"

namespace Sherlock {

/**
 * Decompresses an LZW compressed resource. If no outSize is specified, it will
 * decompress the entire resource. If, however, an explicit size is specified,
 * it will decompress only up to that many bytes from the stream starting at
 * whatever position it was previously.
 */
Common::SeekableReadStream *decompressLZ(Common::SeekableReadStream &source, int32 outSize) {
	if (outSize == -1) {
		source.seek(5);
		outSize = source.readSint32LE();
	}

    byte lzWindow[4096];
    uint16 lzWindowPos;
    uint16 cmd;
    
    byte *outBuffer = new byte[outSize];
    byte *outBufferEnd = outBuffer + outSize;
    Common::MemoryReadStream *outS = new Common::MemoryReadStream(outBuffer, outSize, DisposeAfterUse::YES);
    
    memset(lzWindow, 0xFF, 0xFEE);
    lzWindowPos = 0xFEE;
    cmd = 0;

    while (1) {
        cmd >>= 1;
        if (!(cmd & 0x100)) {
            cmd = source.readByte() | 0xFF00;
        }
        if (cmd & 1) {
            byte literal = source.readByte();
            *outBuffer++ = literal;
            lzWindow[lzWindowPos] = literal;
            lzWindowPos = (lzWindowPos + 1) & 0x0FFF;
        } else {
            int copyPos, copyLen;
            copyPos = source.readByte();
            copyLen = source.readByte();
            copyPos = copyPos | ((copyLen & 0xF0) << 4);
            copyLen = (copyLen & 0x0F) + 3;
            while (copyLen--) {
                byte literal = lzWindow[copyPos];
                copyPos = (copyPos + 1) & 0x0FFF;
                *outBuffer++ = literal;
                lzWindow[lzWindowPos] = literal;
                lzWindowPos = (lzWindowPos + 1) & 0x0FFF;
            }
        }
        if (outBuffer >= outBufferEnd)
            break;
    }

    return outS;
}

} // namespace Sherlock