コード例 #1
0
        private void Initialize(int maxSymbols)
        {
            int numTrees = (int)_bitstream.Read(3);

            if (numTrees < 2 || numTrees > 6)
            {
                throw new InvalidDataException("Invalid number of tables");
            }

            int numSelectors = (int)_bitstream.Read(15);

            if (numSelectors < 1)
            {
                throw new InvalidDataException("Invalid number of selectors");
            }

            _selectors = new byte[numSelectors];
            MoveToFront mtf = new MoveToFront(numTrees, true);

            for (int i = 0; i < numSelectors; ++i)
            {
                _selectors[i] = mtf.GetAndMove(CountSetBits(numTrees));
            }

            _trees = new HuffmanTree[numTrees];
            for (int t = 0; t < numTrees; ++t)
            {
                uint[] lengths = new uint[maxSymbols];

                uint len = _bitstream.Read(5);
                for (int i = 0; i < maxSymbols; ++i)
                {
                    if (len < 1 || len > 20)
                    {
                        throw new InvalidDataException("Invalid length constructing Huffman tree");
                    }

                    while (_bitstream.Read(1) != 0)
                    {
                        len = (_bitstream.Read(1) == 0) ? len + 1 : len - 1;

                        if (len < 1 || len > 20)
                        {
                            throw new InvalidDataException("Invalid length constructing Huffman tree");
                        }
                    }

                    lengths[i] = len;
                }

                _trees[t] = new HuffmanTree(lengths);
            }

            _symbolsToNextSelector = 0;
            _nextSelector          = 0;
        }
コード例 #2
0
        private static int ReadBuffer(BitStream bitstream, byte[] buffer, int offset)
        {
            // The MTF state
            int         numInUse           = 0;
            MoveToFront moveFrontTransform = new MoveToFront();

            bool[] inUseGroups = new bool[16];
            for (int i = 0; i < 16; ++i)
            {
                inUseGroups[i] = bitstream.Read(1) != 0;
            }

            for (int i = 0; i < 256; ++i)
            {
                if (inUseGroups[i / 16])
                {
                    if (bitstream.Read(1) != 0)
                    {
                        moveFrontTransform.Set(numInUse, (byte)i);
                        numInUse++;
                    }
                }
            }

            // Initialize 'virtual' Huffman tree from bitstream
            BZip2CombinedHuffmanTrees huffmanTree = new BZip2CombinedHuffmanTrees(bitstream, numInUse + 2);

            // Main loop reading data
            int readBytes = 0;

            while (true)
            {
                uint symbol = huffmanTree.NextSymbol();

                if (symbol < 2)
                {
                    // RLE, with length stored in a binary-style format
                    uint runLength = 0;
                    int  bitShift  = 0;
                    while (symbol < 2)
                    {
                        runLength += (symbol + 1) << bitShift;
                        bitShift++;

                        symbol = huffmanTree.NextSymbol();
                    }

                    byte b = moveFrontTransform.Head;
                    while (runLength > 0)
                    {
                        buffer[offset + readBytes] = b;
                        ++readBytes;
                        --runLength;
                    }
                }

                if (symbol <= numInUse)
                {
                    // Single byte
                    byte b = moveFrontTransform.GetAndMove((int)symbol - 1);
                    buffer[offset + readBytes] = b;
                    ++readBytes;
                }
                else if (symbol == numInUse + 1)
                {
                    // End of block marker
                    return(readBytes);
                }
                else
                {
                    throw new InvalidDataException("Invalid symbol from Huffman table");
                }
            }
        }