/**
* Read and decode the block's Huffman tables
* @return A decoder for the Huffman stage that uses the decoded tables
* Exception if the input stream reaches EOF before all table data has been read
*/
private BZip2HuffmanStageDecoder ReadHuffmanTables()
{
var tableCodeLengths = new byte[HUFFMAN_MAXIMUM_TABLES, BZip2MTFAndRLE2StageEncoder.HUFFMAN_MAXIMUM_ALPHABET_SIZE];
/* Read Huffman symbol to output byte map */
uint huffmanUsedRanges = bitInputStream.ReadBits(16);
int huffmanSymbolCount = 0;
for (int i = 0; i < 16; i++)
{
if ((huffmanUsedRanges & ((1 << 15) >> i)) == 0)
continue;
for (int j = 0, k = i << 4; j < 16; j++, k++)
{
if (bitInputStream.ReadBoolean())
{
huffmanSymbolMap[huffmanSymbolCount++] = (byte)k;
}
}
}
var endOfBlockSymbol = huffmanSymbolCount + 1;
this.huffmanEndOfBlockSymbol = endOfBlockSymbol;
/* Read total number of tables and selectors*/
uint totalTables = bitInputStream.ReadBits(3);
uint totalSelectors = bitInputStream.ReadBits(15);
if ((totalTables < HUFFMAN_MINIMUM_TABLES)
|| (totalTables > HUFFMAN_MAXIMUM_TABLES)
|| (totalSelectors < 1)
|| (totalSelectors > HUFFMAN_MAXIMUM_SELECTORS))
{
throw new Exception("BZip2 block Huffman tables invalid");
}
/* Read and decode MTFed Huffman selector list */
var tableMTF = new MoveToFront();
var selectors = new byte[totalSelectors];
for (var selector = 0; selector < totalSelectors; selector++)
{
selectors[selector] = tableMTF.IndexToFront((int)bitInputStream.ReadUnary());
}
/* Read the Canonical Huffman code lengths for each table */
for (var table = 0; table < totalTables; table++)
{
int currentLength = (int)bitInputStream.ReadBits(5);
for (var i = 0; i <= endOfBlockSymbol; i++)
{
while (bitInputStream.ReadBoolean())
{
currentLength += bitInputStream.ReadBoolean() ? -1 : 1;
}
tableCodeLengths[table, i] = (byte)currentLength;
}
}
return new BZip2HuffmanStageDecoder(bitInputStream, endOfBlockSymbol + 1, tableCodeLengths, selectors);
}
/**
* Reads the Huffman encoded data from the input stream, performs Run-Length Decoding and
* applies the Move To Front transform to reconstruct the Burrows-Wheeler Transform array
* @param huffmanDecoder The Huffman decoder through which symbols are read
* Exception if an end-of-block symbol was not decoded within the declared block size
*/
private void DecodeHuffmanData(BZip2HuffmanStageDecoder huffmanDecoder)
{
var symbolMTF = new MoveToFront();
int _bwtBlockLength = 0;
int repeatCount = 0;
int repeatIncrement = 1;
int mtfValue = 0;
while (true)
{
var nextSymbol = huffmanDecoder.NextSymbol();
if (nextSymbol == BZip2MTFAndRLE2StageEncoder.RLE_SYMBOL_RUNA)
{
repeatCount += repeatIncrement;
repeatIncrement <<= 1;
}
else if (nextSymbol == BZip2MTFAndRLE2StageEncoder.RLE_SYMBOL_RUNB)
{
repeatCount += repeatIncrement << 1;
repeatIncrement <<= 1;
}
else
{
byte nextByte;
if (repeatCount > 0)
{
if (_bwtBlockLength + repeatCount > this.bwtBlock.Length)
throw new Exception("BZip2 block exceeds declared block size");
nextByte = huffmanSymbolMap[mtfValue];
bwtByteCounts[nextByte & 0xff] += repeatCount;
while (--repeatCount >= 0)
{
bwtBlock[_bwtBlockLength++] = nextByte;
}
repeatCount = 0;
repeatIncrement = 1;
}
if (nextSymbol == huffmanEndOfBlockSymbol)
break;
if (_bwtBlockLength >= this.bwtBlock.Length)
throw new Exception("BZip2 block exceeds declared block size");
mtfValue = symbolMTF.IndexToFront(nextSymbol - 1) & 0xff;
nextByte = huffmanSymbolMap[mtfValue];
bwtByteCounts[nextByte & 0xff]++;
bwtBlock[_bwtBlockLength++] = nextByte;
}
}
this.bwtBlockLength = _bwtBlockLength;
}