private static void Push(UInt16LEOutputBitStream bitStream, bool bit, Stream destination, MemoryStream data)
{
if (bitStream.Push(bit))
{
byte[] bytes = data.ToArray();
destination.Write(bytes, 0, bytes.Length);
data.SetLength(0);
}
}
private static void EncodeInternal(Stream destination, byte[] buffer, long pos, long slidingWindow, long recLength, long size)
{
UInt16LEOutputBitStream bitStream = new UInt16LEOutputBitStream(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 - 1));
}
}
bPointer += iCount;
}
}
Push(bitStream, false, destination, data);
Push(bitStream, true, destination, data);
// If the bit stream was just flushed, write an empty bit stream that will be read just before the end-of-data
// sequence below.
if (!bitStream.HasWaitingBits)
{
NeutralEndian.Write1(data, 0);
NeutralEndian.Write1(data, 0);
}
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);
}
private static void Encode(Stream input, Stream output, Endianness endianness)
{
Action <Stream, ushort> write2;
OutputBitStream <ushort> bitStream;
if (endianness == Endianness.BigEndian)
{
write2 = Write2BE;
bitStream = new UInt16BEOutputBitStream(output);
}
else
{
write2 = Write2LE;
bitStream = new UInt16LEOutputBitStream(output);
}
// To unpack source into 2-byte words.
ushort[] words = new ushort[(input.Length - input.Position) / 2];
if (words.Length == 0)
{
throw new CompressionException(Properties.Resources.EmptySource);
}
// Frequency map.
SortedList <ushort, long> counts = new SortedList <ushort, long>();
// Presence map.
HashSet <ushort> elements = new HashSet <ushort>();
// Unpack source into array. Along the way, build frequency and presence maps.
ushort maskValue = 0;
{
byte[] buffer = new byte[2];
int i = 0, bytesRead;
while ((bytesRead = input.Read(buffer, 0, 2)) == 2)
{
ushort v = (ushort)(buffer[0] << 8 | buffer[1]);
maskValue |= v;
long count;
counts.TryGetValue(v, out count);
counts[v] = count + 1;
elements.Add(v);
words[i++] = v;
}
}
var writeBitfield = GetBitfieldWriter((byte)(maskValue >> 11));
byte packetLength = (byte)(Log2((ushort)(maskValue & 0x7ff)) + 1);
// Find the most common 2-byte value.
ushort commonValue = FindMostFrequentWord(counts);
// Find incrementing (not necessarily contiguous) runs.
// The original algorithm does this for all 65536 2-byte words, while
// this version only checks the 2-byte words actually in the file.
SortedList <ushort, long> runs = new SortedList <ushort, long>();
foreach (ushort element in elements)
{
ushort next = element;
long runLength = 0;
foreach (ushort word in words)
{
if (word == next)
{
++next;
++runLength;
}
}
runs[element] = runLength;
}
// Find the starting 2-byte value with the longest incrementing run.
ushort incrementingValue = FindMostFrequentWord(runs);
// Output header.
NeutralEndian.Write1(output, packetLength);
NeutralEndian.Write1(output, (byte)(maskValue >> 11));
write2(output, incrementingValue);
write2(output, commonValue);
// Output compressed data.
List <ushort> buf = new List <ushort>();
int pos = 0;
while (pos < words.Length)
{
ushort v = words[pos];
if (v == incrementingValue)
{
FlushBuffer(buf, bitStream, writeBitfield, packetLength);
ushort next = (ushort)(v + 1);
ushort count = 0;
for (int i = pos + 1; i < words.Length && count < 0xf; i++)
{
if (next != words[i])
{
break;
}
++next;
++count;
}
bitStream.Write((ushort)(0x00 | count), 6);
incrementingValue = next;
pos += count;
}
else if (v == commonValue)
{
FlushBuffer(buf, bitStream, writeBitfield, packetLength);
ushort count = 0;
for (int i = pos + 1; i < words.Length && count < 0xf; i++)
{
if (v != words[i])
{
break;
}
++count;
}
bitStream.Write((ushort)(0x10 | count), 6);
pos += count;
}
else
{
ushort next;
int delta;
if (pos + 1 < words.Length &&
(next = words[pos + 1]) != incrementingValue &&
((delta = (int)next - (int)v) == -1 || delta == 0 || delta == 1))
{
FlushBuffer(buf, bitStream, writeBitfield, packetLength);
ushort count = 1;
next = (ushort)(next + delta);
for (int i = pos + 2; i < words.Length && count < 0xf; i++)
{
if (next != words[i])
{
break;
}
// If the word is equal to the incrementing word value, stop this run early so we can use the
// incrementing value in the next iteration of the main loop.
if (words[i] == incrementingValue)
{
break;
}
next = (ushort)(next + delta);
++count;
}
if (delta == -1)
{
delta = 2;
}
delta |= 4;
delta <<= 4;
bitStream.Write((ushort)(delta | count), 7);
writeBitfield(bitStream, v);
bitStream.Write((ushort)(v & 0x7ff), packetLength);
pos += count;
}
else
{
if (buf.Count >= 0xf)
{
FlushBuffer(buf, bitStream, writeBitfield, packetLength);
}
buf.Add(v);
}
}
++pos;
}
FlushBuffer(buf, bitStream, writeBitfield, packetLength);
// Terminator
bitStream.Write(0x7f, 7);
bitStream.Flush(false);
}