public static unsafe void ProduceLengths(
BitSource data,
ushort *tree,
ushort literalLengthCodeCount,
byte distanceCodeCount,
byte *literalLengths,
byte *distanceLengths)
{
var valuesToProduce = literalLengthCodeCount + distanceCodeCount;
var valuesProduced = 0;
byte lastValueProduced = 0;
while (valuesProduced < valuesToProduce)
{
byte codeLength = 0;
uint branch = 0;
while (true)
{
var bit = data.CurrentBitValue();
branch = tree[branch * 2 + bit];
if (branch >= TreeNode.Threshold)
{
// Take lower bits
codeLength = (byte)branch;
break;
}
}
//0 - 15: Represent code lengths of 0 - 15
// 16: Copy the previous code length 3 - 6 times.
// The next 2 bits indicate repeat length
// (0 = 3, ... , 3 = 6)
// Example: Codes 8, 16(+2 bits 11),
// 16(+2 bits 10) will expand to
// 12 code lengths of 8(1 + 6 + 5)
// 17: Repeat a code length of 0 for 3 - 10 times.
// (3 bits of length)
// 18: Repeat a code length of 0 for 11 - 138 times
// (7 bits of length)
if (codeLength == 18)
{
ProduceRepeat(0, 11, bitsAsRepeat: 7);
}
else if (codeLength == 17)
{
ProduceRepeat(0, 3, bitsAsRepeat: 3);
}
else if (codeLength == 16)
{
ProduceRepeat(lastValueProduced, 3, bitsAsRepeat: 2);
}
else
{
ProduceValue(codeLength);
}
}
private ushort TraverseTree(ushort *tree, BitSource bitsource)
{
uint branch = 0;
uint availableBits = 0;
ulong bits = 0;
while (branch < TreeNode.Threshold)
{
ulong consumed = 0;
availableBits = (uint)bitsource.AvailableBits();
bits = bitsource.PeekBits();
while (availableBits > consumed && branch < TreeNode.Threshold)
{
var bit = bits & 1;
bits >>= 1;
branch = tree[branch * 2 + bit];
consumed++;
}
bitsource.Consume(consumed);
if (branch < TreeNode.Threshold)
{
var bit = bitsource.CurrentBitValue();
branch = tree[branch * 2 + bit];
}
}
return((ushort)branch);
}
public HuffmanTree(BitSource data)
{
this.data = data;
// Read 5 bits for LiteralLengthCodeCount
this.LiteralLengthCodeCount = (ushort)(data.ReadBitsAsUshort(5) + 257);
// Read 5 bits for DistanceCodeCount
this.DistanceCodeCount = (byte)(data.ReadBitsAsUshort(5) + 1);
// Read 4 bits for CodeLengthCodeCount
this.CodeLengthCodeCount = (byte)(data.ReadBitsAsUshort(4) + 4);
// Read code length intermediate tree data
byte *codeLengthCodes = stackalloc byte[19];
byte *literalLengths = stackalloc byte[AlphabetSize];
byte *distanceLengths = stackalloc byte[DistanceValuesSize];
for (var i = 0; i < this.CodeLengthCodeCount; i++)
{
codeLengthCodes[CodeLengthMapping[i]] = (byte)data.ReadBitsAsUshort(3);
}
// Generate intermediate tree
uint *intermediateTree = stackalloc uint[19];
GenerateTree(codeLengthCodes, (ushort *)intermediateTree, 19);
CodeLengthHuffmanTree.ProduceLengths(
data,
(ushort *)intermediateTree,
this.LiteralLengthCodeCount,
this.DistanceCodeCount,
literalLengths,
distanceLengths);
this.literalLengthTree = NodePool.Rent(GetTreeLength(AlphabetSize), out var lenTreePtr);
this.literalLengthTreeAsUshort = (ushort *)lenTreePtr;
GenerateTree(
literalLengths,
this.literalLengthTreeAsUshort,
AlphabetSize,
DeflateConstants.LengthExtraBits,
257);
this.distanceTree = NodePool.Rent(GetTreeLength(DistanceValuesSize), out var distTreePtr);
this.distanceTreeAsUshort = (ushort *)distTreePtr;
GenerateTree(
distanceLengths,
this.distanceTreeAsUshort,
DistanceValuesSize,
DeflateConstants.DistanceExtraBits);
}
public DeflateBlock(BitSource data)
{
this.Compressed = data;
this.IsFinal = data.IsSet();
this.Type = (BlockType)data.ReadBitsAsUshort(2);
if (this.Type == BlockType.DynamicHuffmanCodes)
{
this.HuffmanTree = new HuffmanTree(data);
}
else if (this.Type == BlockType.FixedHuffmanCodes)
{
this.HuffmanTree = HuffmanTree.Fixed;
}
else
{
this.HuffmanTree = null;
}
}
private static void Consume(ulong bits, BitSource b)
{
b.availableLocalBits -= bits;
b.currentBit += bits;
b.localBits >>= (int)bits;
}