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); }
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); }