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Diffstat (limited to 'media/libjxl/src/lib/jxl/enc_ans.cc')
| -rw-r--r-- | media/libjxl/src/lib/jxl/enc_ans.cc | 1682 |
1 files changed, 1682 insertions, 0 deletions
diff --git a/media/libjxl/src/lib/jxl/enc_ans.cc b/media/libjxl/src/lib/jxl/enc_ans.cc new file mode 100644 index 0000000000..31bd99bee8 --- /dev/null +++ b/media/libjxl/src/lib/jxl/enc_ans.cc @@ -0,0 +1,1682 @@ +// Copyright (c) the JPEG XL Project Authors. All rights reserved. +// +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +#include "lib/jxl/enc_ans.h" + +#include <stdint.h> + +#include <algorithm> +#include <array> +#include <cmath> +#include <limits> +#include <numeric> +#include <type_traits> +#include <unordered_map> +#include <utility> +#include <vector> + +#include "lib/jxl/ans_common.h" +#include "lib/jxl/aux_out.h" +#include "lib/jxl/aux_out_fwd.h" +#include "lib/jxl/base/bits.h" +#include "lib/jxl/dec_ans.h" +#include "lib/jxl/enc_cluster.h" +#include "lib/jxl/enc_context_map.h" +#include "lib/jxl/enc_huffman.h" +#include "lib/jxl/fast_math-inl.h" +#include "lib/jxl/fields.h" + +namespace jxl { + +namespace { + +bool ans_fuzzer_friendly_ = false; + +static const int kMaxNumSymbolsForSmallCode = 4; + +void ANSBuildInfoTable(const ANSHistBin* counts, const AliasTable::Entry* table, + size_t alphabet_size, size_t log_alpha_size, + ANSEncSymbolInfo* info) { + size_t log_entry_size = ANS_LOG_TAB_SIZE - log_alpha_size; + size_t entry_size_minus_1 = (1 << log_entry_size) - 1; + // create valid alias table for empty streams. + for (size_t s = 0; s < std::max<size_t>(1, alphabet_size); ++s) { + const ANSHistBin freq = s == alphabet_size ? ANS_TAB_SIZE : counts[s]; + info[s].freq_ = static_cast<uint16_t>(freq); +#ifdef USE_MULT_BY_RECIPROCAL + if (freq != 0) { + info[s].ifreq_ = + ((1ull << RECIPROCAL_PRECISION) + info[s].freq_ - 1) / info[s].freq_; + } else { + info[s].ifreq_ = 1; // shouldn't matter (symbol shouldn't occur), but... + } +#endif + info[s].reverse_map_.resize(freq); + } + for (int i = 0; i < ANS_TAB_SIZE; i++) { + AliasTable::Symbol s = + AliasTable::Lookup(table, i, log_entry_size, entry_size_minus_1); + info[s.value].reverse_map_[s.offset] = i; + } +} + +float EstimateDataBits(const ANSHistBin* histogram, const ANSHistBin* counts, + size_t len) { + float sum = 0.0f; + int total_histogram = 0; + int total_counts = 0; + for (size_t i = 0; i < len; ++i) { + total_histogram += histogram[i]; + total_counts += counts[i]; + if (histogram[i] > 0) { + JXL_ASSERT(counts[i] > 0); + // += histogram[i] * -log(counts[i]/total_counts) + sum += histogram[i] * + std::max(0.0f, ANS_LOG_TAB_SIZE - FastLog2f(counts[i])); + } + } + if (total_histogram > 0) { + JXL_ASSERT(total_counts == ANS_TAB_SIZE); + } + return sum; +} + +float EstimateDataBitsFlat(const ANSHistBin* histogram, size_t len) { + const float flat_bits = std::max(FastLog2f(len), 0.0f); + int total_histogram = 0; + for (size_t i = 0; i < len; ++i) { + total_histogram += histogram[i]; + } + return total_histogram * flat_bits; +} + +// Static Huffman code for encoding logcounts. The last symbol is used as RLE +// sequence. +static const uint8_t kLogCountBitLengths[ANS_LOG_TAB_SIZE + 2] = { + 5, 4, 4, 4, 4, 4, 3, 3, 3, 3, 3, 6, 7, 7, +}; +static const uint8_t kLogCountSymbols[ANS_LOG_TAB_SIZE + 2] = { + 17, 11, 15, 3, 9, 7, 4, 2, 5, 6, 0, 33, 1, 65, +}; + +// Returns the difference between largest count that can be represented and is +// smaller than "count" and smallest representable count larger than "count". +static int SmallestIncrement(uint32_t count, uint32_t shift) { + int bits = count == 0 ? -1 : FloorLog2Nonzero(count); + int drop_bits = bits - GetPopulationCountPrecision(bits, shift); + return drop_bits < 0 ? 1 : (1 << drop_bits); +} + +template <bool minimize_error_of_sum> +bool RebalanceHistogram(const float* targets, int max_symbol, int table_size, + uint32_t shift, int* omit_pos, ANSHistBin* counts) { + int sum = 0; + float sum_nonrounded = 0.0; + int remainder_pos = 0; // if all of them are handled in first loop + int remainder_log = -1; + for (int n = 0; n < max_symbol; ++n) { + if (targets[n] > 0 && targets[n] < 1.0f) { + counts[n] = 1; + sum_nonrounded += targets[n]; + sum += counts[n]; + } + } + const float discount_ratio = + (table_size - sum) / (table_size - sum_nonrounded); + JXL_ASSERT(discount_ratio > 0); + JXL_ASSERT(discount_ratio <= 1.0f); + // Invariant for minimize_error_of_sum == true: + // abs(sum - sum_nonrounded) + // <= SmallestIncrement(max(targets[])) + max_symbol + for (int n = 0; n < max_symbol; ++n) { + if (targets[n] >= 1.0f) { + sum_nonrounded += targets[n]; + counts[n] = + static_cast<ANSHistBin>(targets[n] * discount_ratio); // truncate + if (counts[n] == 0) counts[n] = 1; + if (counts[n] == table_size) counts[n] = table_size - 1; + // Round the count to the closest nonzero multiple of SmallestIncrement + // (when minimize_error_of_sum is false) or one of two closest so as to + // keep the sum as close as possible to sum_nonrounded. + int inc = SmallestIncrement(counts[n], shift); + counts[n] -= counts[n] & (inc - 1); + // TODO(robryk): Should we rescale targets[n]? + const float target = + minimize_error_of_sum ? (sum_nonrounded - sum) : targets[n]; + if (counts[n] == 0 || + (target > counts[n] + inc / 2 && counts[n] + inc < table_size)) { + counts[n] += inc; + } + sum += counts[n]; + const int count_log = FloorLog2Nonzero(static_cast<uint32_t>(counts[n])); + if (count_log > remainder_log) { + remainder_pos = n; + remainder_log = count_log; + } + } + } + JXL_ASSERT(remainder_pos != -1); + // NOTE: This is the only place where counts could go negative. We could + // detect that, return false and make ANSHistBin uint32_t. + counts[remainder_pos] -= sum - table_size; + *omit_pos = remainder_pos; + return counts[remainder_pos] > 0; +} + +Status NormalizeCounts(ANSHistBin* counts, int* omit_pos, const int length, + const int precision_bits, uint32_t shift, + int* num_symbols, int* symbols) { + const int32_t table_size = 1 << precision_bits; // target sum / table size + uint64_t total = 0; + int max_symbol = 0; + int symbol_count = 0; + for (int n = 0; n < length; ++n) { + total += counts[n]; + if (counts[n] > 0) { + if (symbol_count < kMaxNumSymbolsForSmallCode) { + symbols[symbol_count] = n; + } + ++symbol_count; + max_symbol = n + 1; + } + } + *num_symbols = symbol_count; + if (symbol_count == 0) { + return true; + } + if (symbol_count == 1) { + counts[symbols[0]] = table_size; + return true; + } + if (symbol_count > table_size) + return JXL_FAILURE("Too many entries in an ANS histogram"); + + const float norm = 1.f * table_size / total; + std::vector<float> targets(max_symbol); + for (size_t n = 0; n < targets.size(); ++n) { + targets[n] = norm * counts[n]; + } + if (!RebalanceHistogram<false>(&targets[0], max_symbol, table_size, shift, + omit_pos, counts)) { + // Use an alternative rebalancing mechanism if the one above failed + // to create a histogram that is positive wherever the original one was. + if (!RebalanceHistogram<true>(&targets[0], max_symbol, table_size, shift, + omit_pos, counts)) { + return JXL_FAILURE("Logic error: couldn't rebalance a histogram"); + } + } + return true; +} + +struct SizeWriter { + size_t size = 0; + void Write(size_t num, size_t bits) { size += num; } +}; + +template <typename Writer> +void StoreVarLenUint8(size_t n, Writer* writer) { + JXL_DASSERT(n <= 255); + if (n == 0) { + writer->Write(1, 0); + } else { + writer->Write(1, 1); + size_t nbits = FloorLog2Nonzero(n); + writer->Write(3, nbits); + writer->Write(nbits, n - (1ULL << nbits)); + } +} + +template <typename Writer> +void StoreVarLenUint16(size_t n, Writer* writer) { + JXL_DASSERT(n <= 65535); + if (n == 0) { + writer->Write(1, 0); + } else { + writer->Write(1, 1); + size_t nbits = FloorLog2Nonzero(n); + writer->Write(4, nbits); + writer->Write(nbits, n - (1ULL << nbits)); + } +} + +template <typename Writer> +bool EncodeCounts(const ANSHistBin* counts, const int alphabet_size, + const int omit_pos, const int num_symbols, uint32_t shift, + const int* symbols, Writer* writer) { + bool ok = true; + if (num_symbols <= 2) { + // Small tree marker to encode 1-2 symbols. + writer->Write(1, 1); + if (num_symbols == 0) { + writer->Write(1, 0); + StoreVarLenUint8(0, writer); + } else { + writer->Write(1, num_symbols - 1); + for (int i = 0; i < num_symbols; ++i) { + StoreVarLenUint8(symbols[i], writer); + } + } + if (num_symbols == 2) { + writer->Write(ANS_LOG_TAB_SIZE, counts[symbols[0]]); + } + } else { + // Mark non-small tree. + writer->Write(1, 0); + // Mark non-flat histogram. + writer->Write(1, 0); + + // Precompute sequences for RLE encoding. Contains the number of identical + // values starting at a given index. Only contains the value at the first + // element of the series. + std::vector<uint32_t> same(alphabet_size, 0); + int last = 0; + for (int i = 1; i < alphabet_size; i++) { + // Store the sequence length once different symbol reached, or we're at + // the end, or the length is longer than we can encode, or we are at + // the omit_pos. We don't support including the omit_pos in an RLE + // sequence because this value may use a different amount of log2 bits + // than standard, it is too complex to handle in the decoder. + if (counts[i] != counts[last] || i + 1 == alphabet_size || + (i - last) >= 255 || i == omit_pos || i == omit_pos + 1) { + same[last] = (i - last); + last = i + 1; + } + } + + int length = 0; + std::vector<int> logcounts(alphabet_size); + int omit_log = 0; + for (int i = 0; i < alphabet_size; ++i) { + JXL_ASSERT(counts[i] <= ANS_TAB_SIZE); + JXL_ASSERT(counts[i] >= 0); + if (i == omit_pos) { + length = i + 1; + } else if (counts[i] > 0) { + logcounts[i] = FloorLog2Nonzero(static_cast<uint32_t>(counts[i])) + 1; + length = i + 1; + if (i < omit_pos) { + omit_log = std::max(omit_log, logcounts[i] + 1); + } else { + omit_log = std::max(omit_log, logcounts[i]); + } + } + } + logcounts[omit_pos] = omit_log; + + // Elias gamma-like code for shift. Only difference is that if the number + // of bits to be encoded is equal to FloorLog2(ANS_LOG_TAB_SIZE+1), we skip + // the terminating 0 in unary coding. + int upper_bound_log = FloorLog2Nonzero(ANS_LOG_TAB_SIZE + 1); + int log = FloorLog2Nonzero(shift + 1); + writer->Write(log, (1 << log) - 1); + if (log != upper_bound_log) writer->Write(1, 0); + writer->Write(log, ((1 << log) - 1) & (shift + 1)); + + // Since num_symbols >= 3, we know that length >= 3, therefore we encode + // length - 3. + if (length - 3 > 255) { + // Pretend that everything is OK, but complain about correctness later. + StoreVarLenUint8(255, writer); + ok = false; + } else { + StoreVarLenUint8(length - 3, writer); + } + + // The logcount values are encoded with a static Huffman code. + static const size_t kMinReps = 4; + size_t rep = ANS_LOG_TAB_SIZE + 1; + for (int i = 0; i < length; ++i) { + if (i > 0 && same[i - 1] > kMinReps) { + // Encode the RLE symbol and skip the repeated ones. + writer->Write(kLogCountBitLengths[rep], kLogCountSymbols[rep]); + StoreVarLenUint8(same[i - 1] - kMinReps - 1, writer); + i += same[i - 1] - 2; + continue; + } + writer->Write(kLogCountBitLengths[logcounts[i]], + kLogCountSymbols[logcounts[i]]); + } + for (int i = 0; i < length; ++i) { + if (i > 0 && same[i - 1] > kMinReps) { + // Skip symbols encoded by RLE. + i += same[i - 1] - 2; + continue; + } + if (logcounts[i] > 1 && i != omit_pos) { + int bitcount = GetPopulationCountPrecision(logcounts[i] - 1, shift); + int drop_bits = logcounts[i] - 1 - bitcount; + JXL_CHECK((counts[i] & ((1 << drop_bits) - 1)) == 0); + writer->Write(bitcount, (counts[i] >> drop_bits) - (1 << bitcount)); + } + } + } + return ok; +} + +void EncodeFlatHistogram(const int alphabet_size, BitWriter* writer) { + // Mark non-small tree. + writer->Write(1, 0); + // Mark uniform histogram. + writer->Write(1, 1); + JXL_ASSERT(alphabet_size > 0); + // Encode alphabet size. + StoreVarLenUint8(alphabet_size - 1, writer); +} + +float ComputeHistoAndDataCost(const ANSHistBin* histogram, size_t alphabet_size, + uint32_t method) { + if (method == 0) { // Flat code + return ANS_LOG_TAB_SIZE + 2 + + EstimateDataBitsFlat(histogram, alphabet_size); + } + // Non-flat: shift = method-1. + uint32_t shift = method - 1; + std::vector<ANSHistBin> counts(histogram, histogram + alphabet_size); + int omit_pos = 0; + int num_symbols; + int symbols[kMaxNumSymbolsForSmallCode] = {}; + JXL_CHECK(NormalizeCounts(counts.data(), &omit_pos, alphabet_size, + ANS_LOG_TAB_SIZE, shift, &num_symbols, symbols)); + SizeWriter writer; + // Ignore the correctness, no real encoding happens at this stage. + (void)EncodeCounts(counts.data(), alphabet_size, omit_pos, num_symbols, shift, + symbols, &writer); + return writer.size + + EstimateDataBits(histogram, counts.data(), alphabet_size); +} + +uint32_t ComputeBestMethod( + const ANSHistBin* histogram, size_t alphabet_size, float* cost, + HistogramParams::ANSHistogramStrategy ans_histogram_strategy) { + size_t method = 0; + float fcost = ComputeHistoAndDataCost(histogram, alphabet_size, 0); + auto try_shift = [&](size_t shift) { + float c = ComputeHistoAndDataCost(histogram, alphabet_size, shift + 1); + if (c < fcost) { + method = shift + 1; + fcost = c; + } + }; + switch (ans_histogram_strategy) { + case HistogramParams::ANSHistogramStrategy::kPrecise: { + for (uint32_t shift = 0; shift <= ANS_LOG_TAB_SIZE; shift++) { + try_shift(shift); + } + break; + } + case HistogramParams::ANSHistogramStrategy::kApproximate: { + for (uint32_t shift = 0; shift <= ANS_LOG_TAB_SIZE; shift += 2) { + try_shift(shift); + } + break; + } + case HistogramParams::ANSHistogramStrategy::kFast: { + try_shift(0); + try_shift(ANS_LOG_TAB_SIZE / 2); + try_shift(ANS_LOG_TAB_SIZE); + break; + } + }; + *cost = fcost; + return method; +} + +} // namespace + +// Returns an estimate of the cost of encoding this histogram and the +// corresponding data. +size_t BuildAndStoreANSEncodingData( + HistogramParams::ANSHistogramStrategy ans_histogram_strategy, + const ANSHistBin* histogram, size_t alphabet_size, size_t log_alpha_size, + bool use_prefix_code, ANSEncSymbolInfo* info, BitWriter* writer) { + if (use_prefix_code) { + if (alphabet_size <= 1) return 0; + std::vector<uint32_t> histo(alphabet_size); + for (size_t i = 0; i < alphabet_size; i++) { + histo[i] = histogram[i]; + JXL_CHECK(histogram[i] >= 0); + } + size_t cost = 0; + { + std::vector<uint8_t> depths(alphabet_size); + std::vector<uint16_t> bits(alphabet_size); + BitWriter tmp_writer; + BitWriter* w = writer ? writer : &tmp_writer; + size_t start = w->BitsWritten(); + BitWriter::Allotment allotment( + w, 8 * alphabet_size + 8); // safe upper bound + BuildAndStoreHuffmanTree(histo.data(), alphabet_size, depths.data(), + bits.data(), w); + ReclaimAndCharge(w, &allotment, 0, /*aux_out=*/nullptr); + + for (size_t i = 0; i < alphabet_size; i++) { + info[i].bits = depths[i] == 0 ? 0 : bits[i]; + info[i].depth = depths[i]; + } + cost = w->BitsWritten() - start; + } + // Estimate data cost. + for (size_t i = 0; i < alphabet_size; i++) { + cost += histogram[i] * info[i].depth; + } + return cost; + } + JXL_ASSERT(alphabet_size <= ANS_TAB_SIZE); + // Ensure we ignore trailing zeros in the histogram. + if (alphabet_size != 0) { + size_t largest_symbol = 0; + for (size_t i = 0; i < alphabet_size; i++) { + if (histogram[i] != 0) largest_symbol = i; + } + alphabet_size = largest_symbol + 1; + } + float cost; + uint32_t method = ComputeBestMethod(histogram, alphabet_size, &cost, + ans_histogram_strategy); + JXL_ASSERT(cost >= 0); + int num_symbols; + int symbols[kMaxNumSymbolsForSmallCode] = {}; + std::vector<ANSHistBin> counts(histogram, histogram + alphabet_size); + if (!counts.empty()) { + size_t sum = 0; + for (size_t i = 0; i < counts.size(); i++) { + sum += counts[i]; + } + if (sum == 0) { + counts[0] = ANS_TAB_SIZE; + } + } + if (method == 0) { + counts = CreateFlatHistogram(alphabet_size, ANS_TAB_SIZE); + AliasTable::Entry a[ANS_MAX_ALPHABET_SIZE]; + InitAliasTable(counts, ANS_TAB_SIZE, log_alpha_size, a); + ANSBuildInfoTable(counts.data(), a, alphabet_size, log_alpha_size, info); + if (writer != nullptr) { + EncodeFlatHistogram(alphabet_size, writer); + } + return cost; + } + int omit_pos = 0; + uint32_t shift = method - 1; + JXL_CHECK(NormalizeCounts(counts.data(), &omit_pos, alphabet_size, + ANS_LOG_TAB_SIZE, shift, &num_symbols, symbols)); + AliasTable::Entry a[ANS_MAX_ALPHABET_SIZE]; + InitAliasTable(counts, ANS_TAB_SIZE, log_alpha_size, a); + ANSBuildInfoTable(counts.data(), a, alphabet_size, log_alpha_size, info); + if (writer != nullptr) { + bool ok = EncodeCounts(counts.data(), alphabet_size, omit_pos, num_symbols, + shift, symbols, writer); + (void)ok; + JXL_DASSERT(ok); + } + return cost; +} + +float ANSPopulationCost(const ANSHistBin* data, size_t alphabet_size) { + float c; + ComputeBestMethod(data, alphabet_size, &c, + HistogramParams::ANSHistogramStrategy::kFast); + return c; +} + +template <typename Writer> +void EncodeUintConfig(const HybridUintConfig uint_config, Writer* writer, + size_t log_alpha_size) { + writer->Write(CeilLog2Nonzero(log_alpha_size + 1), + uint_config.split_exponent); + if (uint_config.split_exponent == log_alpha_size) { + return; // msb/lsb don't matter. + } + size_t nbits = CeilLog2Nonzero(uint_config.split_exponent + 1); + writer->Write(nbits, uint_config.msb_in_token); + nbits = CeilLog2Nonzero(uint_config.split_exponent - + uint_config.msb_in_token + 1); + writer->Write(nbits, uint_config.lsb_in_token); +} +template <typename Writer> +void EncodeUintConfigs(const std::vector<HybridUintConfig>& uint_config, + Writer* writer, size_t log_alpha_size) { + // TODO(veluca): RLE? + for (size_t i = 0; i < uint_config.size(); i++) { + EncodeUintConfig(uint_config[i], writer, log_alpha_size); + } +} +template void EncodeUintConfigs(const std::vector<HybridUintConfig>&, + BitWriter*, size_t); + +namespace { + +void ChooseUintConfigs(const HistogramParams& params, + const std::vector<std::vector<Token>>& tokens, + const std::vector<uint8_t>& context_map, + std::vector<Histogram>* clustered_histograms, + EntropyEncodingData* codes, size_t* log_alpha_size) { + codes->uint_config.resize(clustered_histograms->size()); + + if (params.uint_method == HistogramParams::HybridUintMethod::kNone) return; + if (params.uint_method == HistogramParams::HybridUintMethod::k000) { + codes->uint_config.clear(); + codes->uint_config.resize(clustered_histograms->size(), + HybridUintConfig(0, 0, 0)); + return; + } + if (params.uint_method == HistogramParams::HybridUintMethod::kContextMap) { + codes->uint_config.clear(); + codes->uint_config.resize(clustered_histograms->size(), + HybridUintConfig(2, 0, 1)); + return; + } + + // Brute-force method that tries a few options. + std::vector<HybridUintConfig> configs; + if (params.uint_method == HistogramParams::HybridUintMethod::kBest) { + configs = { + HybridUintConfig(4, 2, 0), // default + HybridUintConfig(4, 1, 0), // less precise + HybridUintConfig(4, 2, 1), // add sign + HybridUintConfig(4, 2, 2), // add sign+parity + HybridUintConfig(4, 1, 2), // add parity but less msb + // Same as above, but more direct coding. + HybridUintConfig(5, 2, 0), HybridUintConfig(5, 1, 0), + HybridUintConfig(5, 2, 1), HybridUintConfig(5, 2, 2), + HybridUintConfig(5, 1, 2), + // Same as above, but less direct coding. + HybridUintConfig(3, 2, 0), HybridUintConfig(3, 1, 0), + HybridUintConfig(3, 2, 1), HybridUintConfig(3, 1, 2), + // For near-lossless. + HybridUintConfig(4, 1, 3), HybridUintConfig(5, 1, 4), + HybridUintConfig(5, 2, 3), HybridUintConfig(6, 1, 5), + HybridUintConfig(6, 2, 4), HybridUintConfig(6, 0, 0), + // Other + HybridUintConfig(0, 0, 0), // varlenuint + HybridUintConfig(2, 0, 1), // works well for ctx map + HybridUintConfig(7, 0, 0), // direct coding + HybridUintConfig(8, 0, 0), // direct coding + HybridUintConfig(9, 0, 0), // direct coding + HybridUintConfig(10, 0, 0), // direct coding + HybridUintConfig(11, 0, 0), // direct coding + HybridUintConfig(12, 0, 0), // direct coding + }; + } else if (params.uint_method == HistogramParams::HybridUintMethod::kFast) { + configs = { + HybridUintConfig(4, 2, 0), // default + HybridUintConfig(4, 1, 2), // add parity but less msb + HybridUintConfig(0, 0, 0), // smallest histograms + HybridUintConfig(2, 0, 1), // works well for ctx map + }; + } + + std::vector<float> costs(clustered_histograms->size(), + std::numeric_limits<float>::max()); + std::vector<uint32_t> extra_bits(clustered_histograms->size()); + std::vector<uint8_t> is_valid(clustered_histograms->size()); + size_t max_alpha = + codes->use_prefix_code ? PREFIX_MAX_ALPHABET_SIZE : ANS_MAX_ALPHABET_SIZE; + for (HybridUintConfig cfg : configs) { + std::fill(is_valid.begin(), is_valid.end(), true); + std::fill(extra_bits.begin(), extra_bits.end(), 0); + + for (size_t i = 0; i < clustered_histograms->size(); i++) { + (*clustered_histograms)[i].Clear(); + } + for (size_t i = 0; i < tokens.size(); ++i) { + for (size_t j = 0; j < tokens[i].size(); ++j) { + const Token token = tokens[i][j]; + // TODO(veluca): do not ignore lz77 commands. + if (token.is_lz77_length) continue; + size_t histo = context_map[token.context]; + uint32_t tok, nbits, bits; + cfg.Encode(token.value, &tok, &nbits, &bits); + if (tok >= max_alpha || + (codes->lz77.enabled && tok >= codes->lz77.min_symbol)) { + is_valid[histo] = false; + continue; + } + extra_bits[histo] += nbits; + (*clustered_histograms)[histo].Add(tok); + } + } + + for (size_t i = 0; i < clustered_histograms->size(); i++) { + if (!is_valid[i]) continue; + float cost = (*clustered_histograms)[i].PopulationCost() + extra_bits[i]; + // add signaling cost of the hybriduintconfig itself + cost += CeilLog2Nonzero(cfg.split_exponent + 1); + cost += CeilLog2Nonzero(cfg.split_exponent - cfg.msb_in_token + 1); + if (cost < costs[i]) { + codes->uint_config[i] = cfg; + costs[i] = cost; + } + } + } + + // Rebuild histograms. + for (size_t i = 0; i < clustered_histograms->size(); i++) { + (*clustered_histograms)[i].Clear(); + } + *log_alpha_size = 4; + for (size_t i = 0; i < tokens.size(); ++i) { + for (size_t j = 0; j < tokens[i].size(); ++j) { + const Token token = tokens[i][j]; + uint32_t tok, nbits, bits; + size_t histo = context_map[token.context]; + (token.is_lz77_length ? codes->lz77.length_uint_config + : codes->uint_config[histo]) + .Encode(token.value, &tok, &nbits, &bits); + tok += token.is_lz77_length ? codes->lz77.min_symbol : 0; + (*clustered_histograms)[histo].Add(tok); + while (tok >= (1u << *log_alpha_size)) (*log_alpha_size)++; + } + } +#if JXL_ENABLE_ASSERT + size_t max_log_alpha_size = codes->use_prefix_code ? PREFIX_MAX_BITS : 8; + JXL_ASSERT(*log_alpha_size <= max_log_alpha_size); +#endif +} + +class HistogramBuilder { + public: + explicit HistogramBuilder(const size_t num_contexts) + : histograms_(num_contexts) {} + + void VisitSymbol(int symbol, size_t histo_idx) { + JXL_DASSERT(histo_idx < histograms_.size()); + histograms_[histo_idx].Add(symbol); + } + + // NOTE: `layer` is only for clustered_entropy; caller does ReclaimAndCharge. + size_t BuildAndStoreEntropyCodes( + const HistogramParams& params, + const std::vector<std::vector<Token>>& tokens, EntropyEncodingData* codes, + std::vector<uint8_t>* context_map, bool use_prefix_code, + BitWriter* writer, size_t layer, AuxOut* aux_out) const { + size_t cost = 0; + codes->encoding_info.clear(); + std::vector<Histogram> clustered_histograms(histograms_); + context_map->resize(histograms_.size()); + if (histograms_.size() > 1) { + if (!ans_fuzzer_friendly_) { + std::vector<uint32_t> histogram_symbols; + ClusterHistograms(params, histograms_, histograms_.size(), + kClustersLimit, &clustered_histograms, + &histogram_symbols); + for (size_t c = 0; c < histograms_.size(); ++c) { + (*context_map)[c] = static_cast<uint8_t>(histogram_symbols[c]); + } + } else { + fill(context_map->begin(), context_map->end(), 0); + size_t max_symbol = 0; + for (const Histogram& h : histograms_) { + max_symbol = std::max(h.data_.size(), max_symbol); + } + size_t num_symbols = 1 << CeilLog2Nonzero(max_symbol + 1); + clustered_histograms.resize(1); + clustered_histograms[0].Clear(); + for (size_t i = 0; i < num_symbols; i++) { + clustered_histograms[0].Add(i); + } + } + if (writer != nullptr) { + EncodeContextMap(*context_map, clustered_histograms.size(), writer); + } + } + if (aux_out != nullptr) { + for (size_t i = 0; i < clustered_histograms.size(); ++i) { + aux_out->layers[layer].clustered_entropy += + clustered_histograms[i].ShannonEntropy(); + } + } + codes->use_prefix_code = use_prefix_code; + size_t log_alpha_size = codes->lz77.enabled ? 8 : 7; // Sane default. + if (ans_fuzzer_friendly_) { + codes->uint_config.clear(); + codes->uint_config.resize(1, HybridUintConfig(7, 0, 0)); + } else { + ChooseUintConfigs(params, tokens, *context_map, &clustered_histograms, + codes, &log_alpha_size); + } + if (log_alpha_size < 5) log_alpha_size = 5; + SizeWriter size_writer; // Used if writer == nullptr to estimate costs. + cost += 1; + if (writer) writer->Write(1, use_prefix_code); + + if (use_prefix_code) { + log_alpha_size = PREFIX_MAX_BITS; + } else { + cost += 2; + } + if (writer == nullptr) { + EncodeUintConfigs(codes->uint_config, &size_writer, log_alpha_size); + } else { + if (!use_prefix_code) writer->Write(2, log_alpha_size - 5); + EncodeUintConfigs(codes->uint_config, writer, log_alpha_size); + } + if (use_prefix_code) { + for (size_t c = 0; c < clustered_histograms.size(); ++c) { + size_t num_symbol = 1; + for (size_t i = 0; i < clustered_histograms[c].data_.size(); i++) { + if (clustered_histograms[c].data_[i]) num_symbol = i + 1; + } + if (writer) { + StoreVarLenUint16(num_symbol - 1, writer); + } else { + StoreVarLenUint16(num_symbol - 1, &size_writer); + } + } + } + cost += size_writer.size; + for (size_t c = 0; c < clustered_histograms.size(); ++c) { + size_t num_symbol = 1; + for (size_t i = 0; i < clustered_histograms[c].data_.size(); i++) { + if (clustered_histograms[c].data_[i]) num_symbol = i + 1; + } + codes->encoding_info.emplace_back(); + codes->encoding_info.back().resize(std::max<size_t>(1, num_symbol)); + + BitWriter::Allotment allotment(writer, 256 + num_symbol * 24); + cost += BuildAndStoreANSEncodingData( + params.ans_histogram_strategy, clustered_histograms[c].data_.data(), + num_symbol, log_alpha_size, use_prefix_code, + codes->encoding_info.back().data(), writer); + allotment.FinishedHistogram(writer); + ReclaimAndCharge(writer, &allotment, layer, aux_out); + } + return cost; + } + + const Histogram& Histo(size_t i) const { return histograms_[i]; } + + private: + std::vector<Histogram> histograms_; +}; + +class SymbolCostEstimator { + public: + SymbolCostEstimator(size_t num_contexts, bool force_huffman, + const std::vector<std::vector<Token>>& tokens, + const LZ77Params& lz77) { + HistogramBuilder builder(num_contexts); + // Build histograms for estimating lz77 savings. + HybridUintConfig uint_config; + for (size_t i = 0; i < tokens.size(); ++i) { + for (size_t j = 0; j < tokens[i].size(); ++j) { + const Token token = tokens[i][j]; + uint32_t tok, nbits, bits; + (token.is_lz77_length ? lz77.length_uint_config : uint_config) + .Encode(token.value, &tok, &nbits, &bits); + tok += token.is_lz77_length ? lz77.min_symbol : 0; + builder.VisitSymbol(tok, token.context); + } + } + max_alphabet_size_ = 0; + for (size_t i = 0; i < num_contexts; i++) { + max_alphabet_size_ = + std::max(max_alphabet_size_, builder.Histo(i).data_.size()); + } + bits_.resize(num_contexts * max_alphabet_size_); + // TODO(veluca): SIMD? + add_symbol_cost_.resize(num_contexts); + for (size_t i = 0; i < num_contexts; i++) { + float inv_total = 1.0f / (builder.Histo(i).total_count_ + 1e-8f); + float total_cost = 0; + for (size_t j = 0; j < builder.Histo(i).data_.size(); j++) { + size_t cnt = builder.Histo(i).data_[j]; + float cost = 0; + if (cnt != 0 && cnt != builder.Histo(i).total_count_) { + cost = -FastLog2f(cnt * inv_total); + if (force_huffman) cost = std::ceil(cost); + } else if (cnt == 0) { + cost = ANS_LOG_TAB_SIZE; // Highest possible cost. + } + bits_[i * max_alphabet_size_ + j] = cost; + total_cost += cost * builder.Histo(i).data_[j]; + } + // Penalty for adding a lz77 symbol to this contest (only used for static + // cost model). Higher penalty for contexts that have a very low + // per-symbol entropy. + add_symbol_cost_[i] = std::max(0.0f, 6.0f - total_cost * inv_total); + } + } + float Bits(size_t ctx, size_t sym) const { + return bits_[ctx * max_alphabet_size_ + sym]; + } + float LenCost(size_t ctx, size_t len, const LZ77Params& lz77) const { + uint32_t nbits, bits, tok; + lz77.length_uint_config.Encode(len, &tok, &nbits, &bits); + tok += lz77.min_symbol; + return nbits + Bits(ctx, tok); + } + float DistCost(size_t len, const LZ77Params& lz77) const { + uint32_t nbits, bits, tok; + HybridUintConfig().Encode(len, &tok, &nbits, &bits); + return nbits + Bits(lz77.nonserialized_distance_context, tok); + } + float AddSymbolCost(size_t idx) const { return add_symbol_cost_[idx]; } + + private: + size_t max_alphabet_size_; + std::vector<float> bits_; + std::vector<float> add_symbol_cost_; +}; + +void ApplyLZ77_RLE(const HistogramParams& params, size_t num_contexts, + const std::vector<std::vector<Token>>& tokens, + LZ77Params& lz77, + std::vector<std::vector<Token>>& tokens_lz77) { + // TODO(veluca): tune heuristics here. + SymbolCostEstimator sce(num_contexts, params.force_huffman, tokens, lz77); + float bit_decrease = 0; + size_t total_symbols = 0; + tokens_lz77.resize(tokens.size()); + std::vector<float> sym_cost; + HybridUintConfig uint_config; + for (size_t stream = 0; stream < tokens.size(); stream++) { + size_t distance_multiplier = + params.image_widths.size() > stream ? params.image_widths[stream] : 0; + const auto& in = tokens[stream]; + auto& out = tokens_lz77[stream]; + total_symbols += in.size(); + // Cumulative sum of bit costs. + sym_cost.resize(in.size() + 1); + for (size_t i = 0; i < in.size(); i++) { + uint32_t tok, nbits, unused_bits; + uint_config.Encode(in[i].value, &tok, &nbits, &unused_bits); + sym_cost[i + 1] = sce.Bits(in[i].context, tok) + nbits + sym_cost[i]; + } + out.reserve(in.size()); + for (size_t i = 0; i < in.size(); i++) { + size_t num_to_copy = 0; + size_t distance_symbol = 0; // 1 for RLE. + if (distance_multiplier != 0) { + distance_symbol = 1; // Special distance 1 if enabled. + JXL_DASSERT(kSpecialDistances[1][0] == 1); + JXL_DASSERT(kSpecialDistances[1][1] == 0); + } + if (i > 0) { + for (; i + num_to_copy < in.size(); num_to_copy++) { + if (in[i + num_to_copy].value != in[i - 1].value) { + break; + } + } + } + if (num_to_copy == 0) { + out.push_back(in[i]); + continue; + } + float cost = sym_cost[i + num_to_copy] - sym_cost[i]; + // This subtraction might overflow, but that's OK. + size_t lz77_len = num_to_copy - lz77.min_length; + float lz77_cost = num_to_copy >= lz77.min_length + ? CeilLog2Nonzero(lz77_len + 1) + 1 + : 0; + if (num_to_copy < lz77.min_length || cost <= lz77_cost) { + for (size_t j = 0; j < num_to_copy; j++) { + out.push_back(in[i + j]); + } + i += num_to_copy - 1; + continue; + } + // Output the LZ77 length + out.emplace_back(in[i].context, lz77_len); + out.back().is_lz77_length = true; + i += num_to_copy - 1; + bit_decrease += cost - lz77_cost; + // Output the LZ77 copy distance. + out.emplace_back(lz77.nonserialized_distance_context, distance_symbol); + } + } + + if (bit_decrease > total_symbols * 0.2 + 16) { + lz77.enabled = true; + } +} + +// Hash chain for LZ77 matching +struct HashChain { + size_t size_; + std::vector<uint32_t> data_; + + unsigned hash_num_values_ = 32768; + unsigned hash_mask_ = hash_num_values_ - 1; + unsigned hash_shift_ = 5; + + std::vector<int> head; + std::vector<uint32_t> chain; + std::vector<int> val; + + // Speed up repetitions of zero + std::vector<int> headz; + std::vector<uint32_t> chainz; + std::vector<uint32_t> zeros; + uint32_t numzeros = 0; + + size_t window_size_; + size_t window_mask_; + size_t min_length_; + size_t max_length_; + + // Map of special distance codes. + std::unordered_map<int, int> special_dist_table_; + size_t num_special_distances_ = 0; + + uint32_t maxchainlength = 256; // window_size_ to allow all + + HashChain(const Token* data, size_t size, size_t window_size, + size_t min_length, size_t max_length, size_t distance_multiplier) + : size_(size), + window_size_(window_size), + window_mask_(window_size - 1), + min_length_(min_length), + max_length_(max_length) { + data_.resize(size); + for (size_t i = 0; i < size; i++) { + data_[i] = data[i].value; + } + + head.resize(hash_num_values_, -1); + val.resize(window_size_, -1); + chain.resize(window_size_); + for (uint32_t i = 0; i < window_size_; ++i) { + chain[i] = i; // same value as index indicates uninitialized + } + + zeros.resize(window_size_); + headz.resize(window_size_ + 1, -1); + chainz.resize(window_size_); + for (uint32_t i = 0; i < window_size_; ++i) { + chainz[i] = i; + } + // Translate distance to special distance code. + if (distance_multiplier) { + // Count down, so if due to small distance multiplier multiple distances + // map to the same code, the smallest code will be used in the end. + for (int i = kNumSpecialDistances - 1; i >= 0; --i) { + int xi = kSpecialDistances[i][0]; + int yi = kSpecialDistances[i][1]; + int distance = yi * distance_multiplier + xi; + // Ensure that we map distance 1 to the lowest symbols. + if (distance < 1) distance = 1; + special_dist_table_[distance] = i; + } + num_special_distances_ = kNumSpecialDistances; + } + } + + uint32_t GetHash(size_t pos) const { + uint32_t result = 0; + if (pos + 2 < size_) { + // TODO(lode): take the MSB's of the uint32_t values into account as well, + // given that the hash code itself is less than 32 bits. + result ^= (uint32_t)(data_[pos + 0] << 0u); + result ^= (uint32_t)(data_[pos + 1] << hash_shift_); + result ^= (uint32_t)(data_[pos + 2] << (hash_shift_ * 2)); + } else { + // No need to compute hash of last 2 bytes, the length 2 is too short. + return 0; + } + return result & hash_mask_; + } + + uint32_t CountZeros(size_t pos, uint32_t prevzeros) const { + size_t end = pos + window_size_; + if (end > size_) end = size_; + if (prevzeros > 0) { + if (prevzeros >= window_mask_ && data_[end - 1] == 0 && + end == pos + window_size_) { + return prevzeros; + } else { + return prevzeros - 1; + } + } + uint32_t num = 0; + while (pos + num < end && data_[pos + num] == 0) num++; + return num; + } + + void Update(size_t pos) { + uint32_t hashval = GetHash(pos); + uint32_t wpos = pos & window_mask_; + + val[wpos] = (int)hashval; + if (head[hashval] != -1) chain[wpos] = head[hashval]; + head[hashval] = wpos; + + if (pos > 0 && data_[pos] != data_[pos - 1]) numzeros = 0; + numzeros = CountZeros(pos, numzeros); + + zeros[wpos] = numzeros; + if (headz[numzeros] != -1) chainz[wpos] = headz[numzeros]; + headz[numzeros] = wpos; + } + + void Update(size_t pos, size_t len) { + for (size_t i = 0; i < len; i++) { + Update(pos + i); + } + } + + template <typename CB> + void FindMatches(size_t pos, int max_dist, const CB& found_match) const { + uint32_t wpos = pos & window_mask_; + uint32_t hashval = GetHash(pos); + uint32_t hashpos = chain[wpos]; + + int prev_dist = 0; + int end = std::min<int>(pos + max_length_, size_); + uint32_t chainlength = 0; + uint32_t best_len = 0; + for (;;) { + int dist = (hashpos <= wpos) ? (wpos - hashpos) + : (wpos - hashpos + window_mask_ + 1); + if (dist < prev_dist) break; + prev_dist = dist; + uint32_t len = 0; + if (dist > 0) { + int i = pos; + int j = pos - dist; + if (numzeros > 3) { + int r = std::min<int>(numzeros - 1, zeros[hashpos]); + if (i + r >= end) r = end - i - 1; + i += r; + j += r; + } + while (i < end && data_[i] == data_[j]) { + i++; + j++; + } + len = i - pos; + // This can trigger even if the new length is slightly smaller than the + // best length, because it is possible for a slightly cheaper distance + // symbol to occur. + if (len >= min_length_ && len + 2 >= best_len) { + auto it = special_dist_table_.find(dist); + int dist_symbol = (it == special_dist_table_.end()) + ? (num_special_distances_ + dist - 1) + : it->second; + found_match(len, dist_symbol); + if (len > best_len) best_len = len; + } + } + + chainlength++; + if (chainlength >= maxchainlength) break; + + if (numzeros >= 3 && len > numzeros) { + if (hashpos == chainz[hashpos]) break; + hashpos = chainz[hashpos]; + if (zeros[hashpos] != numzeros) break; + } else { + if (hashpos == chain[hashpos]) break; + hashpos = chain[hashpos]; + if (val[hashpos] != (int)hashval) break; // outdated hash value + } + } + } + void FindMatch(size_t pos, int max_dist, size_t* result_dist_symbol, + size_t* result_len) const { + *result_dist_symbol = 0; + *result_len = 1; + FindMatches(pos, max_dist, [&](size_t len, size_t dist_symbol) { + if (len > *result_len || + (len == *result_len && *result_dist_symbol > dist_symbol)) { + *result_len = len; + *result_dist_symbol = dist_symbol; + } + }); + } +}; + +float LenCost(size_t len) { + uint32_t nbits, bits, tok; + HybridUintConfig(1, 0, 0).Encode(len, &tok, &nbits, &bits); + constexpr float kCostTable[] = { + 2.797667318563126, 3.213177690381199, 2.5706009246743737, + 2.408392498667534, 2.829649191872326, 3.3923087753324577, + 4.029267451554331, 4.415576699706408, 4.509357574741465, + 9.21481543803004, 10.020590190114898, 11.858671627804766, + 12.45853300490526, 11.713105831990857, 12.561996324849314, + 13.775477692278367, 13.174027068768641, + }; + size_t table_size = sizeof kCostTable / sizeof *kCostTable; + if (tok >= table_size) tok = table_size - 1; + return kCostTable[tok] + nbits; +} + +// TODO(veluca): this does not take into account usage or non-usage of distance +// multipliers. +float DistCost(size_t dist) { + uint32_t nbits, bits, tok; + HybridUintConfig(7, 0, 0).Encode(dist, &tok, &nbits, &bits); + constexpr float kCostTable[] = { + 6.368282626312716, 5.680793277090298, 8.347404197105247, + 7.641619201599141, 6.914328374119438, 7.959808291537444, + 8.70023120759855, 8.71378518934703, 9.379132523982769, + 9.110472749092708, 9.159029569270908, 9.430936766731973, + 7.278284055315169, 7.8278514904267755, 10.026641158289236, + 9.976049229827066, 9.64351607048908, 9.563403863480442, + 10.171474111762747, 10.45950155077234, 9.994813912104219, + 10.322524683741156, 8.465808729388186, 8.756254166066853, + 10.160930174662234, 10.247329273413435, 10.04090403724809, + 10.129398517544082, 9.342311691539546, 9.07608009102374, + 10.104799540677513, 10.378079384990906, 10.165828974075072, + 10.337595322341553, 7.940557464567944, 10.575665823319431, + 11.023344321751955, 10.736144698831827, 11.118277044595054, + 7.468468230648442, 10.738305230932939, 10.906980780216568, + 10.163468216353817, 10.17805759656433, 11.167283670483565, + 11.147050200274544, 10.517921919244333, 10.651764778156886, + 10.17074446448919, 11.217636876224745, 11.261630721139484, + 11.403140815247259, 10.892472096873417, 11.1859607804481, + 8.017346947551262, 7.895143720278828, 11.036577113822025, + 11.170562110315794, 10.326988722591086, 10.40872184751056, + 11.213498225466386, 11.30580635516863, 10.672272515665442, + 10.768069466228063, 11.145257364153565, 11.64668307145549, + 10.593156194627339, 11.207499484844943, 10.767517766396908, + 10.826629811407042, 10.737764794499988, 10.6200448518045, + 10.191315385198092, 8.468384171390085, 11.731295299170432, + 11.824619886654398, 10.41518844301179, 10.16310536548649, + 10.539423685097576, 10.495136599328031, 10.469112847728267, + 11.72057686174922, 10.910326337834674, 11.378921834673758, + 11.847759036098536, 11.92071647623854, 10.810628276345282, + 11.008601085273893, 11.910326337834674, 11.949212023423133, + 11.298614839104337, 11.611603659010392, 10.472930394619985, + 11.835564720850282, 11.523267392285337, 12.01055816679611, + 8.413029688994023, 11.895784139536406, 11.984679534970505, + 11.220654278717394, 11.716311684833672, 10.61036646226114, + 10.89849965960364, 10.203762898863669, 10.997560826267238, + 11.484217379438984, 11.792836176993665, 12.24310468755171, + 11.464858097919262, 12.212747017409377, 11.425595666074955, + 11.572048533398757, 12.742093965163013, 11.381874288645637, + 12.191870445817015, 11.683156920035426, 11.152442115262197, + 11.90303691580457, 11.653292787169159, 11.938615382266098, + 16.970641701570223, 16.853602280380002, 17.26240782594733, + 16.644655390108507, 17.14310889757499, 16.910935455445955, + 17.505678976959697, 17.213498225466388, 2.4162310293553024, + 3.494587244462329, 3.5258600986408344, 3.4959806589517095, + 3.098390886949687, 3.343454654302911, 3.588847442290287, + 4.14614790111827, 5.152948641990529, 7.433696808092598, + 9.716311684833672, + }; + size_t table_size = sizeof kCostTable / sizeof *kCostTable; + if (tok >= table_size) tok = table_size - 1; + return kCostTable[tok] + nbits; +} + +void ApplyLZ77_LZ77(const HistogramParams& params, size_t num_contexts, + const std::vector<std::vector<Token>>& tokens, + LZ77Params& lz77, + std::vector<std::vector<Token>>& tokens_lz77) { + // TODO(veluca): tune heuristics here. + SymbolCostEstimator sce(num_contexts, params.force_huffman, tokens, lz77); + float bit_decrease = 0; + size_t total_symbols = 0; + tokens_lz77.resize(tokens.size()); + HybridUintConfig uint_config; + std::vector<float> sym_cost; + for (size_t stream = 0; stream < tokens.size(); stream++) { + size_t distance_multiplier = + params.image_widths.size() > stream ? params.image_widths[stream] : 0; + const auto& in = tokens[stream]; + auto& out = tokens_lz77[stream]; + total_symbols += in.size(); + // Cumulative sum of bit costs. + sym_cost.resize(in.size() + 1); + for (size_t i = 0; i < in.size(); i++) { + uint32_t tok, nbits, unused_bits; + uint_config.Encode(in[i].value, &tok, &nbits, &unused_bits); + sym_cost[i + 1] = sce.Bits(in[i].context, tok) + nbits + sym_cost[i]; + } + + out.reserve(in.size()); + size_t max_distance = in.size(); + size_t min_length = lz77.min_length; + JXL_ASSERT(min_length >= 3); + size_t max_length = in.size(); + + // Use next power of two as window size. + size_t window_size = 1; + while (window_size < max_distance && window_size < kWindowSize) { + window_size <<= 1; + } + + HashChain chain(in.data(), in.size(), window_size, min_length, max_length, + distance_multiplier); + size_t len, dist_symbol; + + const size_t max_lazy_match_len = 256; // 0 to disable lazy matching + + // Whether the next symbol was already updated (to test lazy matching) + bool already_updated = false; + for (size_t i = 0; i < in.size(); i++) { + out.push_back(in[i]); + if (!already_updated) chain.Update(i); + already_updated = false; + chain.FindMatch(i, max_distance, &dist_symbol, &len); + if (len >= min_length) { + if (len < max_lazy_match_len && i + 1 < in.size()) { + // Try length at next symbol lazy matching + chain.Update(i + 1); + already_updated = true; + size_t len2, dist_symbol2; + chain.FindMatch(i + 1, max_distance, &dist_symbol2, &len2); + if (len2 > len) { + // Use the lazy match. Add literal, and use the next length starting + // from the next byte. + ++i; + already_updated = false; + len = len2; + dist_symbol = dist_symbol2; + out.push_back(in[i]); + } + } + + float cost = sym_cost[i + len] - sym_cost[i]; + size_t lz77_len = len - lz77.min_length; + float lz77_cost = LenCost(lz77_len) + DistCost(dist_symbol) + + sce.AddSymbolCost(out.back().context); + + if (lz77_cost <= cost) { + out.back().value = len - min_length; + out.back().is_lz77_length = true; + out.emplace_back(lz77.nonserialized_distance_context, dist_symbol); + bit_decrease += cost - lz77_cost; + } else { + // LZ77 match ignored, and symbol already pushed. Push all other + // symbols and skip. + for (size_t j = 1; j < len; j++) { + out.push_back(in[i + j]); + } + } + + if (already_updated) { + chain.Update(i + 2, len - 2); + already_updated = false; + } else { + chain.Update(i + 1, len - 1); + } + i += len - 1; + } else { + // Literal, already pushed + } + } + } + + if (bit_decrease > total_symbols * 0.2 + 16) { + lz77.enabled = true; + } +} + +void ApplyLZ77_Optimal(const HistogramParams& params, size_t num_contexts, + const std::vector<std::vector<Token>>& tokens, + LZ77Params& lz77, + std::vector<std::vector<Token>>& tokens_lz77) { + std::vector<std::vector<Token>> tokens_for_cost_estimate; + ApplyLZ77_LZ77(params, num_contexts, tokens, lz77, tokens_for_cost_estimate); + // If greedy-LZ77 does not give better compression than no-lz77, no reason to + // run the optimal matching. + if (!lz77.enabled) return; + SymbolCostEstimator sce(num_contexts + 1, params.force_huffman, + tokens_for_cost_estimate, lz77); + tokens_lz77.resize(tokens.size()); + HybridUintConfig uint_config; + std::vector<float> sym_cost; + std::vector<uint32_t> dist_symbols; + for (size_t stream = 0; stream < tokens.size(); stream++) { + size_t distance_multiplier = + params.image_widths.size() > stream ? params.image_widths[stream] : 0; + const auto& in = tokens[stream]; + auto& out = tokens_lz77[stream]; + // Cumulative sum of bit costs. + sym_cost.resize(in.size() + 1); + for (size_t i = 0; i < in.size(); i++) { + uint32_t tok, nbits, unused_bits; + uint_config.Encode(in[i].value, &tok, &nbits, &unused_bits); + sym_cost[i + 1] = sce.Bits(in[i].context, tok) + nbits + sym_cost[i]; + } + + out.reserve(in.size()); + size_t max_distance = in.size(); + size_t min_length = lz77.min_length; + JXL_ASSERT(min_length >= 3); + size_t max_length = in.size(); + + // Use next power of two as window size. + size_t window_size = 1; + while (window_size < max_distance && window_size < kWindowSize) { + window_size <<= 1; + } + + HashChain chain(in.data(), in.size(), window_size, min_length, max_length, + distance_multiplier); + + struct MatchInfo { + uint32_t len; + uint32_t dist_symbol; + uint32_t ctx; + float total_cost = std::numeric_limits<float>::max(); + }; + // Total cost to encode the first N symbols. + std::vector<MatchInfo> prefix_costs(in.size() + 1); + prefix_costs[0].total_cost = 0; + + size_t rle_length = 0; + size_t skip_lz77 = 0; + for (size_t i = 0; i < in.size(); i++) { + chain.Update(i); + float lit_cost = + prefix_costs[i].total_cost + sym_cost[i + 1] - sym_cost[i]; + if (prefix_costs[i + 1].total_cost > lit_cost) { + prefix_costs[i + 1].dist_symbol = 0; + prefix_costs[i + 1].len = 1; + prefix_costs[i + 1].ctx = in[i].context; + prefix_costs[i + 1].total_cost = lit_cost; + } + if (skip_lz77 > 0) { + skip_lz77--; + continue; + } + dist_symbols.clear(); + chain.FindMatches(i, max_distance, + [&dist_symbols](size_t len, size_t dist_symbol) { + if (dist_symbols.size() <= len) { + dist_symbols.resize(len + 1, dist_symbol); + } + if (dist_symbol < dist_symbols[len]) { + dist_symbols[len] = dist_symbol; + } + }); + if (dist_symbols.size() <= min_length) continue; + { + size_t best_cost = dist_symbols.back(); + for (size_t j = dist_symbols.size() - 1; j >= min_length; j--) { + if (dist_symbols[j] < best_cost) { + best_cost = dist_symbols[j]; + } + dist_symbols[j] = best_cost; + } + } + for (size_t j = min_length; j < dist_symbols.size(); j++) { + // Cost model that uses results from lazy LZ77. + float lz77_cost = sce.LenCost(in[i].context, j - min_length, lz77) + + sce.DistCost(dist_symbols[j], lz77); + float cost = prefix_costs[i].total_cost + lz77_cost; + if (prefix_costs[i + j].total_cost > cost) { + prefix_costs[i + j].len = j; + prefix_costs[i + j].dist_symbol = dist_symbols[j] + 1; + prefix_costs[i + j].ctx = in[i].context; + prefix_costs[i + j].total_cost = cost; + } + } + // We are in a RLE sequence: skip all the symbols except the first 8 and + // the last 8. This avoid quadratic costs for sequences with long runs of + // the same symbol. + if ((dist_symbols.back() == 0 && distance_multiplier == 0) || + (dist_symbols.back() == 1 && distance_multiplier != 0)) { + rle_length++; + } else { + rle_length = 0; + } + if (rle_length >= 8 && dist_symbols.size() > 9) { + skip_lz77 = dist_symbols.size() - 10; + rle_length = 0; + } + } + size_t pos = in.size(); + while (pos > 0) { + bool is_lz77_length = prefix_costs[pos].dist_symbol != 0; + if (is_lz77_length) { + size_t dist_symbol = prefix_costs[pos].dist_symbol - 1; + out.emplace_back(lz77.nonserialized_distance_context, dist_symbol); + } + size_t val = is_lz77_length ? prefix_costs[pos].len - min_length + : in[pos - 1].value; + out.emplace_back(prefix_costs[pos].ctx, val); + out.back().is_lz77_length = is_lz77_length; + pos -= prefix_costs[pos].len; + } + std::reverse(out.begin(), out.end()); + } +} + +void ApplyLZ77(const HistogramParams& params, size_t num_contexts, + const std::vector<std::vector<Token>>& tokens, LZ77Params& lz77, + std::vector<std::vector<Token>>& tokens_lz77) { + lz77.enabled = false; + if (params.force_huffman) { + lz77.min_symbol = std::min(PREFIX_MAX_ALPHABET_SIZE - 32, 512); + } else { + lz77.min_symbol = 224; + } + if (params.lz77_method == HistogramParams::LZ77Method::kNone) { + return; + } else if (params.lz77_method == HistogramParams::LZ77Method::kRLE) { + ApplyLZ77_RLE(params, num_contexts, tokens, lz77, tokens_lz77); + } else if (params.lz77_method == HistogramParams::LZ77Method::kLZ77) { + ApplyLZ77_LZ77(params, num_contexts, tokens, lz77, tokens_lz77); + } else if (params.lz77_method == HistogramParams::LZ77Method::kOptimal) { + ApplyLZ77_Optimal(params, num_contexts, tokens, lz77, tokens_lz77); + } else { + JXL_ABORT("Not implemented"); + } +} +} // namespace + +size_t BuildAndEncodeHistograms(const HistogramParams& params, + size_t num_contexts, + std::vector<std::vector<Token>>& tokens, + EntropyEncodingData* codes, + std::vector<uint8_t>* context_map, + BitWriter* writer, size_t layer, + AuxOut* aux_out) { + size_t total_bits = 0; + codes->lz77.nonserialized_distance_context = num_contexts; + std::vector<std::vector<Token>> tokens_lz77; + ApplyLZ77(params, num_contexts, tokens, codes->lz77, tokens_lz77); + if (ans_fuzzer_friendly_) { + codes->lz77.length_uint_config = HybridUintConfig(10, 0, 0); + codes->lz77.min_symbol = 2048; + } + + const size_t max_contexts = std::min(num_contexts, kClustersLimit); + BitWriter::Allotment allotment(writer, + 128 + num_contexts * 40 + max_contexts * 96); + if (writer) { + JXL_CHECK(Bundle::Write(codes->lz77, writer, layer, aux_out)); + } else { + size_t ebits, bits; + JXL_CHECK(Bundle::CanEncode(codes->lz77, &ebits, &bits)); + total_bits += bits; + } + if (codes->lz77.enabled) { + if (writer) { + size_t b = writer->BitsWritten(); + EncodeUintConfig(codes->lz77.length_uint_config, writer, + /*log_alpha_size=*/8); + total_bits += writer->BitsWritten() - b; + } else { + SizeWriter size_writer; + EncodeUintConfig(codes->lz77.length_uint_config, &size_writer, + /*log_alpha_size=*/8); + total_bits += size_writer.size; + } + num_contexts += 1; + tokens = std::move(tokens_lz77); + } + size_t total_tokens = 0; + // Build histograms. + HistogramBuilder builder(num_contexts); + HybridUintConfig uint_config; // Default config for clustering. + // Unless we are using the kContextMap histogram option. + if (params.uint_method == HistogramParams::HybridUintMethod::kContextMap) { + uint_config = HybridUintConfig(2, 0, 1); + } + if (params.uint_method == HistogramParams::HybridUintMethod::k000) { + uint_config = HybridUintConfig(0, 0, 0); + } + if (ans_fuzzer_friendly_) { + uint_config = HybridUintConfig(10, 0, 0); + } + for (size_t i = 0; i < tokens.size(); ++i) { + if (codes->lz77.enabled) { + for (size_t j = 0; j < tokens[i].size(); ++j) { + const Token& token = tokens[i][j]; + total_tokens++; + uint32_t tok, nbits, bits; + (token.is_lz77_length ? codes->lz77.length_uint_config : uint_config) + .Encode(token.value, &tok, &nbits, &bits); + tok += token.is_lz77_length ? codes->lz77.min_symbol : 0; + builder.VisitSymbol(tok, token.context); + } + } else if (num_contexts == 1) { + for (size_t j = 0; j < tokens[i].size(); ++j) { + const Token& token = tokens[i][j]; + total_tokens++; + uint32_t tok, nbits, bits; + uint_config.Encode(token.value, &tok, &nbits, &bits); + builder.VisitSymbol(tok, /*token.context=*/0); + } + } else { + for (size_t j = 0; j < tokens[i].size(); ++j) { + const Token& token = tokens[i][j]; + total_tokens++; + uint32_t tok, nbits, bits; + uint_config.Encode(token.value, &tok, &nbits, &bits); + builder.VisitSymbol(tok, token.context); + } + } + } + + bool use_prefix_code = + params.force_huffman || total_tokens < 100 || + params.clustering == HistogramParams::ClusteringType::kFastest || + ans_fuzzer_friendly_; + if (!use_prefix_code) { + bool all_singleton = true; + for (size_t i = 0; i < num_contexts; i++) { + if (builder.Histo(i).ShannonEntropy() >= 1e-5) { + all_singleton = false; + } + } + if (all_singleton) { + use_prefix_code = true; + } + } + + // Encode histograms. + total_bits += builder.BuildAndStoreEntropyCodes(params, tokens, codes, + context_map, use_prefix_code, + writer, layer, aux_out); + allotment.FinishedHistogram(writer); + ReclaimAndCharge(writer, &allotment, layer, aux_out); + + if (aux_out != nullptr) { + aux_out->layers[layer].num_clustered_histograms += + codes->encoding_info.size(); + } + return total_bits; +} + +size_t WriteTokens(const std::vector<Token>& tokens, + const EntropyEncodingData& codes, + const std::vector<uint8_t>& context_map, BitWriter* writer) { + size_t num_extra_bits = 0; + if (codes.use_prefix_code) { + for (size_t i = 0; i < tokens.size(); i++) { + uint32_t tok, nbits, bits; + const Token& token = tokens[i]; + size_t histo = context_map[token.context]; + (token.is_lz77_length ? codes.lz77.length_uint_config + : codes.uint_config[histo]) + .Encode(token.value, &tok, &nbits, &bits); + tok += token.is_lz77_length ? codes.lz77.min_symbol : 0; + // Combine two calls to the BitWriter. Equivalent to: + // writer->Write(codes.encoding_info[histo][tok].depth, + // codes.encoding_info[histo][tok].bits); + // writer->Write(nbits, bits); + uint64_t data = codes.encoding_info[histo][tok].bits; + data |= bits << codes.encoding_info[histo][tok].depth; + writer->Write(codes.encoding_info[histo][tok].depth + nbits, data); + num_extra_bits += nbits; + } + return num_extra_bits; + } + std::vector<uint64_t> out; + std::vector<uint8_t> out_nbits; + out.reserve(tokens.size()); + out_nbits.reserve(tokens.size()); + uint64_t allbits = 0; + size_t numallbits = 0; + // Writes in *reversed* order. + auto addbits = [&](size_t bits, size_t nbits) { + if (JXL_UNLIKELY(nbits)) { + JXL_DASSERT(bits >> nbits == 0); + if (JXL_UNLIKELY(numallbits + nbits > BitWriter::kMaxBitsPerCall)) { + out.push_back(allbits); + out_nbits.push_back(numallbits); + numallbits = allbits = 0; + } + allbits <<= nbits; + allbits |= bits; + numallbits += nbits; + } + }; + const int end = tokens.size(); + ANSCoder ans; + if (codes.lz77.enabled || context_map.size() > 1) { + for (int i = end - 1; i >= 0; --i) { + const Token token = tokens[i]; + const uint8_t histo = context_map[token.context]; + uint32_t tok, nbits, bits; + (token.is_lz77_length ? codes.lz77.length_uint_config + : codes.uint_config[histo]) + .Encode(tokens[i].value, &tok, &nbits, &bits); + tok += token.is_lz77_length ? codes.lz77.min_symbol : 0; + const ANSEncSymbolInfo& info = codes.encoding_info[histo][tok]; + // Extra bits first as this is reversed. + addbits(bits, nbits); + num_extra_bits += nbits; + uint8_t ans_nbits = 0; + uint32_t ans_bits = ans.PutSymbol(info, &ans_nbits); + addbits(ans_bits, ans_nbits); + } + } else { + for (int i = end - 1; i >= 0; --i) { + uint32_t tok, nbits, bits; + codes.uint_config[0].Encode(tokens[i].value, &tok, &nbits, &bits); + const ANSEncSymbolInfo& info = codes.encoding_info[0][tok]; + // Extra bits first as this is reversed. + addbits(bits, nbits); + num_extra_bits += nbits; + uint8_t ans_nbits = 0; + uint32_t ans_bits = ans.PutSymbol(info, &ans_nbits); + addbits(ans_bits, ans_nbits); + } + } + const uint32_t state = ans.GetState(); + writer->Write(32, state); + writer->Write(numallbits, allbits); + for (int i = out.size(); i > 0; --i) { + writer->Write(out_nbits[i - 1], out[i - 1]); + } + return num_extra_bits; +} + +void WriteTokens(const std::vector<Token>& tokens, + const EntropyEncodingData& codes, + const std::vector<uint8_t>& context_map, BitWriter* writer, + size_t layer, AuxOut* aux_out) { + BitWriter::Allotment allotment(writer, 32 * tokens.size() + 32 * 1024 * 4); + size_t num_extra_bits = WriteTokens(tokens, codes, context_map, writer); + ReclaimAndCharge(writer, &allotment, layer, aux_out); + if (aux_out != nullptr) { + aux_out->layers[layer].extra_bits += num_extra_bits; + } +} + +void SetANSFuzzerFriendly(bool ans_fuzzer_friendly) { +#if JXL_IS_DEBUG_BUILD // Guard against accidental / malicious changes. + ans_fuzzer_friendly_ = ans_fuzzer_friendly; +#endif +} +} // namespace jxl |