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// 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.
// Library to encode the context map.
#include "lib/jxl/enc_context_map.h"
#include <stdint.h>
#include <algorithm>
#include <cstddef>
#include <vector>
#include "lib/jxl/base/bits.h"
#include "lib/jxl/base/status.h"
#include "lib/jxl/enc_ans.h"
#include "lib/jxl/enc_aux_out.h"
#include "lib/jxl/entropy_coder.h"
namespace jxl {
namespace {
size_t IndexOf(const std::vector<uint8_t>& v, uint8_t value) {
size_t i = 0;
for (; i < v.size(); ++i) {
if (v[i] == value) return i;
}
return i;
}
void MoveToFront(std::vector<uint8_t>* v, size_t index) {
uint8_t value = (*v)[index];
for (size_t i = index; i != 0; --i) {
(*v)[i] = (*v)[i - 1];
}
(*v)[0] = value;
}
std::vector<uint8_t> MoveToFrontTransform(const std::vector<uint8_t>& v) {
if (v.empty()) return v;
uint8_t max_value = *std::max_element(v.begin(), v.end());
std::vector<uint8_t> mtf(max_value + 1);
for (size_t i = 0; i <= max_value; ++i) mtf[i] = i;
std::vector<uint8_t> result(v.size());
for (size_t i = 0; i < v.size(); ++i) {
size_t index = IndexOf(mtf, v[i]);
JXL_ASSERT(index < mtf.size());
result[i] = static_cast<uint8_t>(index);
MoveToFront(&mtf, index);
}
return result;
}
} // namespace
void EncodeContextMap(const std::vector<uint8_t>& context_map,
size_t num_histograms, BitWriter* writer, size_t layer,
AuxOut* aux_out) {
if (num_histograms == 1) {
// Simple code
writer->Write(1, 1);
// 0 bits per entry.
writer->Write(2, 0);
return;
}
std::vector<uint8_t> transformed_symbols = MoveToFrontTransform(context_map);
std::vector<std::vector<Token>> tokens(1), mtf_tokens(1);
EntropyEncodingData codes;
std::vector<uint8_t> dummy_context_map;
for (size_t i = 0; i < context_map.size(); i++) {
tokens[0].emplace_back(0, context_map[i]);
}
for (size_t i = 0; i < transformed_symbols.size(); i++) {
mtf_tokens[0].emplace_back(0, transformed_symbols[i]);
}
HistogramParams params;
params.uint_method = HistogramParams::HybridUintMethod::kContextMap;
size_t ans_cost = BuildAndEncodeHistograms(
params, 1, tokens, &codes, &dummy_context_map, nullptr, 0, nullptr);
size_t mtf_cost = BuildAndEncodeHistograms(
params, 1, mtf_tokens, &codes, &dummy_context_map, nullptr, 0, nullptr);
bool use_mtf = mtf_cost < ans_cost;
// Rebuild token list.
tokens[0].clear();
for (size_t i = 0; i < transformed_symbols.size(); i++) {
tokens[0].emplace_back(0,
use_mtf ? transformed_symbols[i] : context_map[i]);
}
size_t entry_bits = CeilLog2Nonzero(num_histograms);
size_t simple_cost = entry_bits * context_map.size();
if (entry_bits < 4 && simple_cost < ans_cost && simple_cost < mtf_cost) {
writer->Write(1, 1);
writer->Write(2, entry_bits);
for (size_t i = 0; i < context_map.size(); i++) {
writer->Write(entry_bits, context_map[i]);
}
} else {
writer->Write(1, 0);
writer->Write(1, use_mtf); // Use/don't use MTF.
BuildAndEncodeHistograms(params, 1, tokens, &codes, &dummy_context_map,
writer, layer, aux_out);
WriteTokens(tokens[0], codes, dummy_context_map, writer);
}
}
void EncodeBlockCtxMap(const BlockCtxMap& block_ctx_map, BitWriter* writer,
AuxOut* aux_out) {
auto& dct = block_ctx_map.dc_thresholds;
auto& qft = block_ctx_map.qf_thresholds;
auto& ctx_map = block_ctx_map.ctx_map;
BitWriter::Allotment allotment(
writer,
(dct[0].size() + dct[1].size() + dct[2].size() + qft.size()) * 34 + 1 +
4 + 4 + ctx_map.size() * 10 + 1024);
if (dct[0].empty() && dct[1].empty() && dct[2].empty() && qft.empty() &&
ctx_map.size() == 21 &&
std::equal(ctx_map.begin(), ctx_map.end(), BlockCtxMap::kDefaultCtxMap)) {
writer->Write(1, 1); // default
allotment.ReclaimAndCharge(writer, kLayerAC, aux_out);
return;
}
writer->Write(1, 0);
for (int j : {0, 1, 2}) {
writer->Write(4, dct[j].size());
for (int i : dct[j]) {
JXL_CHECK(U32Coder::Write(kDCThresholdDist, PackSigned(i), writer));
}
}
writer->Write(4, qft.size());
for (uint32_t i : qft) {
JXL_CHECK(U32Coder::Write(kQFThresholdDist, i - 1, writer));
}
EncodeContextMap(ctx_map, block_ctx_map.num_ctxs, writer, kLayerAC, aux_out);
allotment.ReclaimAndCharge(writer, kLayerAC, aux_out);
}
} // namespace jxl
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