private static void CreateNodesFromCommand(int command, int byteCount, ChunkNodeCollection nodeCollection, int i, ChunkNode parentNode)
{
byteCount = Codec.GetValidatedSuperCommandSize(byteCount);
if (byteCount > Codec.NormalCommandMax)
{
int reducedByteCount = Math.Min(byteCount, Codec.NormalCommandMax);
nodeCollection.Add(i + reducedByteCount, new ChunkNode(parentNode, command, i, reducedByteCount));
}
nodeCollection.Add(i + byteCount, new ChunkNode(parentNode, command, i, byteCount));
}
private static void CreateChildNodes(byte[] buffer, ChunkNodeCollection nodeCollection, int i, ChunkNode parentNode, ByteDictionary byteDictionary)
{
// NOTE: Command 5 (ie: the same as command 4 except it inverts each byte)
// is not implemented, because it's almost never used.
// Implementing it would complicate the code and slow down the compression for little to no benefit.
// NOTE: Checking out command 0 every time (ie: putting it out of the if conditions)
// can improve compression a tiny bit (like just one byte) in some rare cases,
// but it's not worth the huge hit on compression speed.
OptimalCompressor.CreateNodesFromBackCommands(nodeCollection, i, parentNode, byteDictionary);
int command;
int byteCount;
if ((i + 1) < buffer.Length &&
buffer[i] == buffer[i + 1])
{
command = 1;
byteCount = OptimalCompressor.GetCommand1ByteCount(buffer, i);
}
else if ((i + 2) < buffer.Length &&
buffer[i] == buffer[i + 2])
{
command = 2;
byteCount = OptimalCompressor.GetCommand2ByteCount(buffer, i);
}
else if ((i + 1) < buffer.Length &&
((buffer[i] + 1) & 0xFF) == buffer[i + 1])
{
command = 3;
byteCount = OptimalCompressor.GetCommand3ByteCount(buffer, i);
}
else
{
command = 0;
byteCount = OptimalCompressor.GetCommand0ByteCount(buffer, i);
}
OptimalCompressor.CreateNodesFromCommand(command, byteCount, nodeCollection, i, parentNode);
}
public byte[] Compress(byte[] buffer)
{
ByteDictionary byteDictionary = new ByteDictionary(buffer);
ChunkNodeCollection nodeCollection = new ChunkNodeCollection();
while (nodeCollection.Count > 0)
{
if (nodeCollection.IsNextNodeOptimal())
{
KeyValuePair <int, ChunkNode> parentNode = nodeCollection.GetNextNode();
if (parentNode.Key < buffer.Length)
{
OptimalCompressor.CreateChildNodes(buffer, nodeCollection, parentNode.Key, parentNode.Value, byteDictionary);
}
}
}
ChunkNode bestNode = nodeCollection[buffer.Length];
return(bestNode.GetCompressedBuffer(buffer));
}
private static void CreateNodesFromBackCommands(ChunkNodeCollection nodeCollection, int i, ChunkNode parentNode, ByteDictionary byteDictionary)
{
Range[] ranges = byteDictionary.GetMaxBackRanges(i);
if (ranges[0].Length > 0)
{
nodeCollection.Add(i + ranges[0].Length, new ChunkNode(parentNode, 4, ranges[0].Start, ranges[0].Length));
}
if (ranges[1].Length > 0)
{
nodeCollection.Add(i + ranges[1].Length, new ChunkNode(parentNode, 4, ranges[1].Start, ranges[1].Length));
}
if (ranges[2].Length > 0)
{
nodeCollection.Add(i + ranges[2].Length, new ChunkNode(parentNode, 6, i - ranges[2].Start, ranges[2].Length));
}
if (ranges[3].Length > 0)
{
nodeCollection.Add(i + ranges[3].Length, new ChunkNode(parentNode, 6, i - ranges[3].Start, ranges[3].Length));
}
}
