/*
Calculates the bit lengths for the symbols for dynamic blocks. Chooses bit
lengths that give the smallest size of tree encoding + encoding of all the
symbols to have smallest output size. This are not necessarily the ideal Huffman
bit lengths.
*/
static void GetDynamicLengths(const ZopfliLZ77Store* lz77,
size_t lstart, size_t lend,
unsigned* ll_lengths, unsigned* d_lengths) {
size_t ll_counts[ZOPFLI_NUM_LL];
size_t d_counts[ZOPFLI_NUM_D];
ZopfliLZ77GetHistogram(lz77, lstart, lend, ll_counts, d_counts);
ll_counts[256] = 1; /* End symbol. */
OptimizeHuffmanForRle(ZOPFLI_NUM_LL, ll_counts);
OptimizeHuffmanForRle(ZOPFLI_NUM_D, d_counts);
ZopfliCalculateBitLengths(ll_counts, ZOPFLI_NUM_LL, 15, ll_lengths);
ZopfliCalculateBitLengths(d_counts, ZOPFLI_NUM_D, 15, d_lengths);
PatchDistanceCodesForBuggyDecoders(d_lengths);
}
/*
Calculates the bit lengths for the symbols for dynamic blocks. Chooses bit
lengths that give the smallest size of tree encoding + encoding of all the
symbols to have smallest output size. This are not necessarily the ideal Huffman
bit lengths.
*/
static void GetDynamicLengths(const unsigned short* litlens,
const unsigned short* dists,
size_t lstart, size_t lend,
unsigned* ll_lengths, unsigned* d_lengths) {
size_t ll_counts[288];
size_t d_counts[32];
ZopfliLZ77Counts(litlens, dists, lstart, lend, ll_counts, d_counts);
OptimizeHuffmanForRle(288, ll_counts);
OptimizeHuffmanForRle(32, d_counts);
ZopfliCalculateBitLengths(ll_counts, 288, 15, ll_lengths);
ZopfliCalculateBitLengths(d_counts, 32, 15, d_lengths);
PatchDistanceCodesForBuggyDecoders(d_lengths);
}
void VP8LCreateHuffmanTree(uint32_t* const histogram, int tree_depth_limit,
uint8_t* const buf_rle,
HuffmanTree* const huff_tree,
HuffmanTreeCode* const huff_code) {
const int num_symbols = huff_code->num_symbols;
memset(buf_rle, 0, num_symbols * sizeof(*buf_rle));
OptimizeHuffmanForRle(num_symbols, buf_rle, histogram);
GenerateOptimalTree(histogram, num_symbols, huff_tree, tree_depth_limit,
huff_code->code_lengths);
// Create the actual bit codes for the bit lengths.
ConvertBitDepthsToSymbols(huff_code);
}
int VP8LCreateHuffmanTree(int* const histogram, int tree_depth_limit,
HuffmanTreeCode* const tree) {
const int num_symbols = tree->num_symbols;
if (!OptimizeHuffmanForRle(num_symbols, histogram)) {
return 0;
}
if (!GenerateOptimalTree(histogram, num_symbols,
tree_depth_limit, tree->code_lengths)) {
return 0;
}
// Create the actual bit codes for the bit lengths.
ConvertBitDepthsToSymbols(tree);
return 1;
}
/*
Tries out OptimizeHuffmanForRle for this block, if the result is smaller,
uses it, otherwise keeps the original. Returns size of encoded tree and data in
bits, not including the 3-bit block header.
*/
static double TryOptimizeHuffmanForRle(
const ZopfliLZ77Store* lz77, size_t lstart, size_t lend,
const size_t* ll_counts, const size_t* d_counts,
unsigned* ll_lengths, unsigned* d_lengths) {
size_t ll_counts2[ZOPFLI_NUM_LL];
size_t d_counts2[ZOPFLI_NUM_D];
unsigned ll_lengths2[ZOPFLI_NUM_LL];
unsigned d_lengths2[ZOPFLI_NUM_D];
double treesize;
double datasize;
double treesize2;
double datasize2;
treesize = CalculateTreeSize(ll_lengths, d_lengths);
datasize = CalculateBlockSymbolSizeGivenCounts(ll_counts, d_counts,
ll_lengths, d_lengths, lz77, lstart, lend);
memcpy(ll_counts2, ll_counts, sizeof(ll_counts2));
memcpy(d_counts2, d_counts, sizeof(d_counts2));
OptimizeHuffmanForRle(ZOPFLI_NUM_LL, ll_counts2);
OptimizeHuffmanForRle(ZOPFLI_NUM_D, d_counts2);
ZopfliCalculateBitLengths(ll_counts2, ZOPFLI_NUM_LL, 15, ll_lengths2);
ZopfliCalculateBitLengths(d_counts2, ZOPFLI_NUM_D, 15, d_lengths2);
PatchDistanceCodesForBuggyDecoders(d_lengths2);
treesize2 = CalculateTreeSize(ll_lengths2, d_lengths2);
datasize2 = CalculateBlockSymbolSizeGivenCounts(ll_counts, d_counts,
ll_lengths2, d_lengths2, lz77, lstart, lend);
if (treesize2 + datasize2 < treesize + datasize) {
memcpy(ll_lengths, ll_lengths2, sizeof(ll_lengths2));
memcpy(d_lengths, d_lengths2, sizeof(d_lengths2));
return treesize2 + datasize2;
}
return treesize + datasize;
}