Beispiel #1
0
        private static void EncodeInternal(Stream destination, byte[] buffer, int pos, int size)
        {
            /*
             * Here we create and populate the "LZSS graph":
             *
             * Each value in the uncompressed file forms a node in this graph.
             * The various edges between these nodes represent LZSS matches.
             *
             * Using a shortest-path algorithm, these edges can be used to
             * find the optimal combination of matches needed to produce the
             * smallest possible file.
             *
             * The outputted array only contains one edge per node: the optimal
             * one. This means, in order to produce the smallest file, you just
             * have to traverse the graph from one edge to the next, encoding
             * each match as you go along.
             */

            LZSSGraphEdge[] node_meta_array = new LZSSGraphEdge[size + 1];

            // Initialise the array
            node_meta_array[0].cost = 0;
            for (int i = 1; i < size + 1; ++i)
            {
                node_meta_array[i].cost = int.MaxValue;
            }

            // Find matches
            for (int i = 0; i < size; ++i)
            {
                int max_read_ahead  = Math.Min(0x100 + 8, size - i);
                int max_read_behind = Math.Max(0, i - 0x2000);

                // Search for dictionary matches
                for (int j = i; j-- > max_read_behind;)
                {
                    for (int k = 0; k < max_read_ahead; ++k)
                    {
                        if (buffer[pos + i + k] == buffer[pos + j + k])
                        {
                            int distance = i - j;
                            int length   = k + 1;

                            // Get the cost of the match (or bail if it can't be compressed)
                            int cost;
                            if (length >= 2 && length <= 5 && distance <= 256)
                            {
                                cost = 2 + 2 + 8;   // Descriptor bits, length bits, offset byte
                            }
                            else if (length >= 3 && length <= 9)
                            {
                                cost = 2 + 16;      // Descriptor bits, offset/length bytes
                            }
                            else if (length >= 10)
                            {
                                cost = 2 + 16 + 8;  // Descriptor bits, offset bytes, length byte
                            }
                            else
                            {
                                continue;           // In the event a match cannot be compressed
                            }
                            // Update this node's optimal edge if this one is better
                            if (node_meta_array[i + k + 1].cost > node_meta_array[i].cost + cost)
                            {
                                node_meta_array[i + k + 1].cost = node_meta_array[i].cost + cost;
                                node_meta_array[i + k + 1].previous_node_index = i;
                                node_meta_array[i + k + 1].match_length        = k + 1;
                                node_meta_array[i + k + 1].match_offset        = j;
                            }
                        }
                        else
                        {
                            break;
                        }
                    }
                }

                // Do literal match
                // Update this node's optimal edge if this one is better (or the same, since literal matches usually decode faster)
                if (node_meta_array[i + 1].cost >= node_meta_array[i].cost + 1 + 8)
                {
                    node_meta_array[i + 1].cost = node_meta_array[i].cost + 1 + 8;
                    node_meta_array[i + 1].previous_node_index = i;
                    node_meta_array[i + 1].match_length        = 0;
                }
            }

            // Reverse the edge link order, so the array can be traversed from start to end, rather than vice versa
            node_meta_array[0].previous_node_index = int.MaxValue;
            node_meta_array[size].next_node_index  = int.MaxValue;
            for (int node_index = size; node_meta_array[node_index].previous_node_index != int.MaxValue; node_index = node_meta_array[node_index].previous_node_index)
            {
                node_meta_array[node_meta_array[node_index].previous_node_index].next_node_index = node_index;
            }

            /*
             * LZSS graph complete
             */

            UInt8_NE_H_OutputBitStream bitStream = new UInt8_NE_H_OutputBitStream(destination);
            MemoryStream data = new MemoryStream();

            for (int node_index = 0; node_meta_array[node_index].next_node_index != int.MaxValue; node_index = node_meta_array[node_index].next_node_index)
            {
                int next_index = node_meta_array[node_index].next_node_index;

                int length   = node_meta_array[next_index].match_length;
                int distance = next_index - node_meta_array[next_index].match_length - node_meta_array[next_index].match_offset;

                if (length != 0)
                {
                    if (length >= 2 && length <= 5 && distance <= 256)
                    {
                        Push(bitStream, false, destination, data);
                        Push(bitStream, false, destination, data);
                        NeutralEndian.Write1(data, (byte)-distance);
                        Push(bitStream, ((length - 2) & 2) != 0, destination, data);
                        Push(bitStream, ((length - 2) & 1) != 0, destination, data);
                    }
                    else if (length >= 3 && length <= 9)
                    {
                        Push(bitStream, false, destination, data);
                        Push(bitStream, true, destination, data);
                        NeutralEndian.Write1(data, (byte)(((-distance >> (8 - 3)) & 0xF8) | ((10 - length) & 7)));
                        NeutralEndian.Write1(data, (byte)(-distance & 0xFF));
                    }
                    else //if (length >= 3)
                    {
                        Push(bitStream, false, destination, data);
                        Push(bitStream, true, destination, data);
                        NeutralEndian.Write1(data, (byte)((-distance >> (8 - 3)) & 0xF8));
                        NeutralEndian.Write1(data, (byte)(-distance & 0xFF));
                        NeutralEndian.Write1(data, (byte)(length - 9));
                    }
                }
                else
                {
                    Push(bitStream, true, destination, data);
                    NeutralEndian.Write1(data, buffer[pos + node_index]);
                }
            }

            Push(bitStream, false, destination, data);
            Push(bitStream, true, destination, data);

            NeutralEndian.Write1(data, 0xF0);
            NeutralEndian.Write1(data, 0);
            NeutralEndian.Write1(data, 0);
            bitStream.Flush(true);

            byte[] bytes = data.ToArray();
            destination.Write(bytes, 0, bytes.Length);
        }
Beispiel #2
0
        private static void EncodeInternal(Stream destination, byte[] buffer, long pos, long slidingWindow, long recLength, long size)
        {
            UInt8_NE_H_OutputBitStream bitStream = new UInt8_NE_H_OutputBitStream(destination);
            MemoryStream data = new MemoryStream();

            if (size > 0)
            {
                long bPointer = 1, iOffset = 0;
                bitStream.Push(true);
                NeutralEndian.Write1(data, buffer[pos]);

                while (bPointer < size)
                {
                    long iCount = Math.Min(recLength, size - bPointer);
                    long iMax   = Math.Max(bPointer - slidingWindow, 0);
                    long k      = 1;
                    long i      = bPointer - 1;

                    do
                    {
                        long j = 0;
                        while (buffer[pos + i + j] == buffer[pos + bPointer + j])
                        {
                            if (++j >= iCount)
                            {
                                break;
                            }
                        }

                        if (j > k)
                        {
                            k       = j;
                            iOffset = i;
                        }
                    } while (i-- > iMax);

                    iCount = k;

                    if (iCount == 1)
                    {
                        Push(bitStream, true, destination, data);
                        NeutralEndian.Write1(data, buffer[pos + bPointer]);
                    }
                    else if (iCount == 2 && bPointer - iOffset > 256)
                    {
                        Push(bitStream, true, destination, data);
                        NeutralEndian.Write1(data, buffer[pos + bPointer]);
                        --iCount;
                    }
                    else if (iCount < 6 && bPointer - iOffset <= 256)
                    {
                        Push(bitStream, false, destination, data);
                        Push(bitStream, false, destination, data);
                        Push(bitStream, (((iCount - 2) >> 1) & 1) != 0, destination, data);
                        Push(bitStream, ((iCount - 2) & 1) != 0, destination, data);
                        NeutralEndian.Write1(data, (byte)(~(bPointer - iOffset - 1)));
                    }
                    else
                    {
                        Push(bitStream, false, destination, data);
                        Push(bitStream, true, destination, data);

                        long   off  = bPointer - iOffset - 1;
                        ushort info = (ushort)(~((off << 8) | (off >> 5)) & 0xFFF8);

                        if (iCount < 10) // iCount - 2 < 8
                        {
                            info |= (ushort)(iCount - 2);
                            BigEndian.Write2(data, info);
                        }
                        else
                        {
                            BigEndian.Write2(data, info);
                            NeutralEndian.Write1(data, (byte)(iCount - 9));
                        }
                    }

                    bPointer += iCount;
                }
            }

            Push(bitStream, false, destination, data);
            Push(bitStream, true, destination, data);

            NeutralEndian.Write1(data, 0);
            NeutralEndian.Write1(data, 0xF0);
            NeutralEndian.Write1(data, 0);
            bitStream.Flush(true);

            byte[] bytes = data.ToArray();
            destination.Write(bytes, 0, bytes.Length);
        }