/// <summary>
/// For handling dynamic Huffman codes.
/// </summary>
/// <returns>A sequence of <see cref="CodeTree" /> items.</returns>
private CodeTree[] DecodeHuffmanCodes()
{
var numLitLenCodes = this.ReadInt(5) + 257; // hlit + 257
var numDistCodes = this.ReadInt(5) + 1; // hdist + 1
var numCodeLenCodes = this.ReadInt(4) + 4; // hclen + 4
var codeLenCodeLen = new int[19];
codeLenCodeLen[16] = this.ReadInt(3);
codeLenCodeLen[17] = this.ReadInt(3);
codeLenCodeLen[18] = this.ReadInt(3);
codeLenCodeLen[0] = this.ReadInt(3);
for (var i = 0; i < numCodeLenCodes - 4; i++)
{
if (i % 2 == 0)
{
codeLenCodeLen[8 + (i / 2)] = this.ReadInt(3);
}
else
{
codeLenCodeLen[7 - (i / 2)] = this.ReadInt(3);
}
}
var codeLenCode = new CanonicalCode(codeLenCodeLen).ToCodeTree();
var codeLens = new int[numLitLenCodes + numDistCodes];
var runVal = -1;
var runLen = 0;
for (var i = 0; i < codeLens.Length; i++)
{
if (runLen > 0)
{
codeLens[i] = runVal;
runLen--;
}
else
{
var sym = this.DecodeSymbol(codeLenCode);
if (sym < 16)
{
codeLens[i] = sym;
runVal = sym;
}
else
{
if (sym == 16)
{
if (runVal == -1)
{
throw new FormatException("No code length value to copy");
}
runLen = this.ReadInt(2) + 3;
}
else if (sym == 17)
{
runVal = 0;
runLen = this.ReadInt(3) + 3;
}
else if (sym == 18)
{
runVal = 0;
runLen = this.ReadInt(7) + 11;
}
else
{
throw new Exception();
}
i--;
}
}
}
if (runLen > 0)
{
throw new FormatException("Run exceeds number of codes");
}
// Create code trees
var litLenCodeLen = Arrays.CopyOf(codeLens, numLitLenCodes);
var litLenCode = new CanonicalCode(litLenCodeLen).ToCodeTree();
var distCodeLen = Arrays.CopyOfRange(codeLens, numLitLenCodes, codeLens.Length);
CodeTree distCode;
if (distCodeLen.Length == 1 && distCodeLen[0] == 0)
{
distCode = null; // Empty distance code; the block shall be all literal symbols
}
else
{
distCode = new CanonicalCode(distCodeLen).ToCodeTree();
}
return new[] { litLenCode, distCode };
}
/// <summary>
/// For handling dynamic Huffman codes.
/// </summary>
/// <returns>A sequence of <see cref="CodeTree" /> items.</returns>
private CodeTree[] DecodeHuffmanCodes()
{
var numLitLenCodes = this.ReadInt(5) + 257; // hlit + 257
var numDistCodes = this.ReadInt(5) + 1; // hdist + 1
var numCodeLenCodes = this.ReadInt(4) + 4; // hclen + 4
var codeLenCodeLen = new int[19];
codeLenCodeLen[16] = this.ReadInt(3);
codeLenCodeLen[17] = this.ReadInt(3);
codeLenCodeLen[18] = this.ReadInt(3);
codeLenCodeLen[0] = this.ReadInt(3);
for (var i = 0; i < numCodeLenCodes - 4; i++)
{
if (i % 2 == 0)
{
codeLenCodeLen[8 + (i / 2)] = this.ReadInt(3);
}
else
{
codeLenCodeLen[7 - (i / 2)] = this.ReadInt(3);
}
}
var codeLenCode = new CanonicalCode(codeLenCodeLen).ToCodeTree();
var codeLens = new int[numLitLenCodes + numDistCodes];
var runVal = -1;
var runLen = 0;
for (var i = 0; i < codeLens.Length; i++)
{
if (runLen > 0)
{
codeLens[i] = runVal;
runLen--;
}
else
{
var sym = this.DecodeSymbol(codeLenCode);
if (sym < 16)
{
codeLens[i] = sym;
runVal = sym;
}
else
{
if (sym == 16)
{
if (runVal == -1)
{
throw new FormatException("No code length value to copy");
}
runLen = this.ReadInt(2) + 3;
}
else if (sym == 17)
{
runVal = 0;
runLen = this.ReadInt(3) + 3;
}
else if (sym == 18)
{
runVal = 0;
runLen = this.ReadInt(7) + 11;
}
else
{
throw new Exception();
}
i--;
}
}
}
if (runLen > 0)
{
throw new FormatException("Run exceeds number of codes");
}
// Create code trees
var litLenCodeLen = Arrays.CopyOf(codeLens, numLitLenCodes);
var litLenCode = new CanonicalCode(litLenCodeLen).ToCodeTree();
var distCodeLen = Arrays.CopyOfRange(codeLens, numLitLenCodes, codeLens.Length);
CodeTree distCode;
if (distCodeLen.Length == 1 && distCodeLen[0] == 0)
{
distCode = null; // Empty distance code; the block shall be all literal symbols
}
else
{
distCode = new CanonicalCode(distCodeLen).ToCodeTree();
}
return(new[] { litLenCode, distCode });
}
