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);
}