private void ReadLengths(HuffmanTree preTree, uint[] lengths, int offset, int count)
{
int i = 0;
while (i < count)
{
uint value = preTree.NextSymbol(_bitStream);
if (value == 17)
{
uint numZeros = 4 + _bitStream.Read(4);
for (uint j = 0; j < numZeros; ++j)
{
lengths[offset + i] = 0;
++i;
}
}
else if (value == 18)
{
uint numZeros = 20 + _bitStream.Read(5);
for (uint j = 0; j < numZeros; ++j)
{
lengths[offset + i] = 0;
++i;
}
}
else if (value == 19)
{
uint same = _bitStream.Read(1);
value = preTree.NextSymbol(_bitStream);
if (value > 16)
{
throw new InvalidDataException("Invalid table encoding");
}
uint symbol = (17 + lengths[offset + i] - value) % 17;
for (uint j = 0; j < 4 + same; ++j)
{
lengths[offset + i] = symbol;
++i;
}
}
else
{
lengths[offset + i] = (17 + lengths[offset + i] - value) % 17;
++i;
}
}
}
private void ReadLengths(HuffmanTree preTree, uint[] lengths, int offset, int count)
{
int i = 0;
while (i < count)
{
uint value = preTree.NextSymbol(_bitStream);
if (value == 17)
{
uint numZeros = 4 + _bitStream.Read(4);
for (uint j = 0; j < numZeros; ++j)
{
lengths[offset + i] = 0;
++i;
}
}
else if (value == 18)
{
uint numZeros = 20 + _bitStream.Read(5);
for (uint j = 0; j < numZeros; ++j)
{
lengths[offset + i] = 0;
++i;
}
}
else if (value == 19)
{
uint same = _bitStream.Read(1);
value = preTree.NextSymbol(_bitStream);
if (value > 16)
{
throw new InvalidDataException("Invalid table encoding");
}
uint symbol = (17 + lengths[offset + i] - value) % 17;
for (uint j = 0; j < 4 + same; ++j)
{
lengths[offset + i] = symbol;
++i;
}
}
else
{
lengths[offset + i] = (17 + lengths[offset + i] - value) % 17;
++i;
}
}
}
private byte[] Buffer(int count)
{
byte[] buffer = new byte[count];
int numRead = 0;
HuffmanTree tree = ReadHuffmanTree();
XpressBitStream bitStream = new XpressBitStream(_compressedStream);
while (numRead < count)
{
uint symbol = tree.NextSymbol(bitStream);
if (symbol < 256)
{
// The first 256 symbols are literal byte values
buffer[numRead] = (byte)symbol;
numRead++;
}
else
{
// The next 256 symbols are 4 bits each for offset and length.
int offsetBits = (int)((symbol - 256) / 16);
int len = (int)((symbol - 256) % 16);
// The actual offset
int offset = (int)((1 << offsetBits) - 1 + bitStream.Read(offsetBits));
// Lengths up to 15 bytes are stored directly in the symbol bits, beyond that
// the length is stored in the compression stream.
if (len == 15)
{
// Note this access is directly to the underlying stream - we're not going
// through the bit stream. This makes the precise behaviour of the bit stream,
// in terms of read-ahead critical.
int b = ReadCompressedByte();
if (b == 0xFF)
{
// Again, note this access is directly to the underlying stream - we're not going
// through the bit stream.
len = ReadCompressedUShort();
}
else
{
len += b;
}
}
// Minimum length for a match is 3 bytes, so all lengths are stored as an offset
// from 3.
len += 3;
// Simply do the copy
for (int i = 0; i < len; ++i)
{
buffer[numRead] = buffer[numRead - offset - 1];
numRead++;
}
}
}
return(buffer);
}
private void DecodeCompressedBlock(BlockType blockType, int blockSize)
{
if (blockType == BlockType.AlignedOffset)
{
_alignedOffsetTree = ReadFixedHuffmanTree(8, 3);
}
ReadMainTree();
ReadLengthTree();
uint numRead = 0;
while (numRead < (uint)blockSize)
{
uint symbol = _mainTree.NextSymbol(_bitStream);
if (symbol < 256)
{
_buffer[_bufferCount + numRead++] = (byte)symbol;
}
else
{
uint lengthHeader = (symbol - 256) & 7;
uint matchLength = lengthHeader + 2 + ((lengthHeader == 7) ? _lengthTree.NextSymbol(_bitStream) : 0);
uint positionSlot = (symbol - 256) >> 3;
uint matchOffset;
if (positionSlot == 0)
{
matchOffset = _repeatedOffsets[0];
}
else if (positionSlot == 1)
{
matchOffset = _repeatedOffsets[1];
_repeatedOffsets[1] = _repeatedOffsets[0];
_repeatedOffsets[0] = matchOffset;
}
else if (positionSlot == 2)
{
matchOffset = _repeatedOffsets[2];
_repeatedOffsets[2] = _repeatedOffsets[0];
_repeatedOffsets[0] = matchOffset;
}
else
{
int extra = (int)s_extraBits[positionSlot];
uint formattedOffset;
if (blockType == BlockType.AlignedOffset)
{
uint verbatimBits = 0;
uint alignedBits = 0;
if (extra >= 3)
{
verbatimBits = _bitStream.Read(extra - 3) << 3;
alignedBits = _alignedOffsetTree.NextSymbol(_bitStream);
}
else if (extra > 0)
{
verbatimBits = _bitStream.Read(extra);
}
formattedOffset = s_positionSlots[positionSlot] + verbatimBits + alignedBits;
}
else
{
uint verbatimBits = (extra > 0) ? _bitStream.Read(extra) : 0;
formattedOffset = s_positionSlots[positionSlot] + verbatimBits;
}
matchOffset = formattedOffset - 2;
_repeatedOffsets[2] = _repeatedOffsets[1];
_repeatedOffsets[1] = _repeatedOffsets[0];
_repeatedOffsets[0] = matchOffset;
}
int destOffset = _bufferCount + (int)numRead;
int srcOffset = destOffset - (int)matchOffset;
for (int i = 0; i < matchLength; ++i)
{
_buffer[destOffset + i] = _buffer[srcOffset + i];
}
numRead += matchLength;
}
}
}