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 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;
}