/// <summary>
/// Get the actual bit values for a tree of bit depths.
/// </summary>
/// <param name="tree">The huffman tree.</param>
private static void ConvertBitDepthsToSymbols(HuffmanTreeCode tree)
{
// 0 bit-depth means that the symbol does not exist.
uint[] nextCode = new uint[WebpConstants.MaxAllowedCodeLength + 1];
int[] depthCount = new int[WebpConstants.MaxAllowedCodeLength + 1];
int len = tree.NumSymbols;
for (int i = 0; i < len; i++)
{
int codeLength = tree.CodeLengths[i];
depthCount[codeLength]++;
}
depthCount[0] = 0; // ignore unused symbol.
nextCode[0] = 0;
uint code = 0;
for (int i = 1; i <= WebpConstants.MaxAllowedCodeLength; i++)
{
code = (uint)((code + depthCount[i - 1]) << 1);
nextCode[i] = code;
}
for (int i = 0; i < len; i++)
{
int codeLength = tree.CodeLengths[i];
tree.Codes[i] = (short)ReverseBits(codeLength, nextCode[codeLength]++);
}
}
public static int CreateCompressedHuffmanTree(HuffmanTreeCode tree, HuffmanTreeToken[] tokensArray)
{
int depthSize = tree.NumSymbols;
int prevValue = 8; // 8 is the initial value for rle.
int i = 0;
int tokenPos = 0;
while (i < depthSize)
{
int value = tree.CodeLengths[i];
int k = i + 1;
while (k < depthSize && tree.CodeLengths[k] == value)
{
k++;
}
int runs = k - i;
if (value == 0)
{
tokenPos += CodeRepeatedZeros(runs, tokensArray.AsSpan(tokenPos));
}
else
{
tokenPos += CodeRepeatedValues(runs, tokensArray.AsSpan(tokenPos), value, prevValue);
prevValue = value;
}
i += runs;
}
return(tokenPos);
}
public static void CreateHuffmanTree(uint[] histogram, int treeDepthLimit, bool[] bufRle, HuffmanTree[] huffTree, HuffmanTreeCode huffCode)
{
int numSymbols = huffCode.NumSymbols;
bufRle.AsSpan().Clear();
OptimizeHuffmanForRle(numSymbols, bufRle, histogram);
GenerateOptimalTree(huffTree, histogram, numSymbols, treeDepthLimit, huffCode.CodeLengths);
// Create the actual bit codes for the bit lengths.
ConvertBitDepthsToSymbols(huffCode);
}