diff options
Diffstat (limited to 'third_party/jpeg-xl/lib/jxl/enc_huffman.cc')
| -rw-r--r-- | third_party/jpeg-xl/lib/jxl/enc_huffman.cc | 214 |
1 files changed, 214 insertions, 0 deletions
diff --git a/third_party/jpeg-xl/lib/jxl/enc_huffman.cc b/third_party/jpeg-xl/lib/jxl/enc_huffman.cc new file mode 100644 index 0000000000..3eab2c218a --- /dev/null +++ b/third_party/jpeg-xl/lib/jxl/enc_huffman.cc @@ -0,0 +1,214 @@ +// 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_huffman.h" + +#include <algorithm> +#include <memory> + +#include "lib/jxl/enc_huffman_tree.h" + +namespace jxl { + +namespace { + +constexpr int kCodeLengthCodes = 18; + +void StoreHuffmanTreeOfHuffmanTreeToBitMask(const int num_codes, + const uint8_t* code_length_bitdepth, + BitWriter* writer) { + static const uint8_t kStorageOrder[kCodeLengthCodes] = { + 1, 2, 3, 4, 0, 5, 17, 6, 16, 7, 8, 9, 10, 11, 12, 13, 14, 15}; + // The bit lengths of the Huffman code over the code length alphabet + // are compressed with the following static Huffman code: + // Symbol Code + // ------ ---- + // 0 00 + // 1 1110 + // 2 110 + // 3 01 + // 4 10 + // 5 1111 + static const uint8_t kHuffmanBitLengthHuffmanCodeSymbols[6] = {0, 7, 3, + 2, 1, 15}; + static const uint8_t kHuffmanBitLengthHuffmanCodeBitLengths[6] = {2, 4, 3, + 2, 2, 4}; + + // Throw away trailing zeros: + size_t codes_to_store = kCodeLengthCodes; + if (num_codes > 1) { + for (; codes_to_store > 0; --codes_to_store) { + if (code_length_bitdepth[kStorageOrder[codes_to_store - 1]] != 0) { + break; + } + } + } + size_t skip_some = 0; // skips none. + if (code_length_bitdepth[kStorageOrder[0]] == 0 && + code_length_bitdepth[kStorageOrder[1]] == 0) { + skip_some = 2; // skips two. + if (code_length_bitdepth[kStorageOrder[2]] == 0) { + skip_some = 3; // skips three. + } + } + writer->Write(2, skip_some); + for (size_t i = skip_some; i < codes_to_store; ++i) { + size_t l = code_length_bitdepth[kStorageOrder[i]]; + writer->Write(kHuffmanBitLengthHuffmanCodeBitLengths[l], + kHuffmanBitLengthHuffmanCodeSymbols[l]); + } +} + +void StoreHuffmanTreeToBitMask(const size_t huffman_tree_size, + const uint8_t* huffman_tree, + const uint8_t* huffman_tree_extra_bits, + const uint8_t* code_length_bitdepth, + const uint16_t* code_length_bitdepth_symbols, + BitWriter* writer) { + for (size_t i = 0; i < huffman_tree_size; ++i) { + size_t ix = huffman_tree[i]; + writer->Write(code_length_bitdepth[ix], code_length_bitdepth_symbols[ix]); + // Extra bits + switch (ix) { + case 16: + writer->Write(2, huffman_tree_extra_bits[i]); + break; + case 17: + writer->Write(3, huffman_tree_extra_bits[i]); + break; + } + } +} + +void StoreSimpleHuffmanTree(const uint8_t* depths, size_t symbols[4], + size_t num_symbols, size_t max_bits, + BitWriter* writer) { + // value of 1 indicates a simple Huffman code + writer->Write(2, 1); + writer->Write(2, num_symbols - 1); // NSYM - 1 + + // Sort + for (size_t i = 0; i < num_symbols; i++) { + for (size_t j = i + 1; j < num_symbols; j++) { + if (depths[symbols[j]] < depths[symbols[i]]) { + std::swap(symbols[j], symbols[i]); + } + } + } + + if (num_symbols == 2) { + writer->Write(max_bits, symbols[0]); + writer->Write(max_bits, symbols[1]); + } else if (num_symbols == 3) { + writer->Write(max_bits, symbols[0]); + writer->Write(max_bits, symbols[1]); + writer->Write(max_bits, symbols[2]); + } else { + writer->Write(max_bits, symbols[0]); + writer->Write(max_bits, symbols[1]); + writer->Write(max_bits, symbols[2]); + writer->Write(max_bits, symbols[3]); + // tree-select + writer->Write(1, depths[symbols[0]] == 1 ? 1 : 0); + } +} + +// num = alphabet size +// depths = symbol depths +void StoreHuffmanTree(const uint8_t* depths, size_t num, BitWriter* writer) { + // Write the Huffman tree into the compact representation. + std::unique_ptr<uint8_t[]> arena(new uint8_t[2 * num]); + uint8_t* huffman_tree = arena.get(); + uint8_t* huffman_tree_extra_bits = arena.get() + num; + size_t huffman_tree_size = 0; + WriteHuffmanTree(depths, num, &huffman_tree_size, huffman_tree, + huffman_tree_extra_bits); + + // Calculate the statistics of the Huffman tree in the compact representation. + uint32_t huffman_tree_histogram[kCodeLengthCodes] = {0}; + for (size_t i = 0; i < huffman_tree_size; ++i) { + ++huffman_tree_histogram[huffman_tree[i]]; + } + + int num_codes = 0; + int code = 0; + for (int i = 0; i < kCodeLengthCodes; ++i) { + if (huffman_tree_histogram[i]) { + if (num_codes == 0) { + code = i; + num_codes = 1; + } else if (num_codes == 1) { + num_codes = 2; + break; + } + } + } + + // Calculate another Huffman tree to use for compressing both the + // earlier Huffman tree with. + uint8_t code_length_bitdepth[kCodeLengthCodes] = {0}; + uint16_t code_length_bitdepth_symbols[kCodeLengthCodes] = {0}; + CreateHuffmanTree(&huffman_tree_histogram[0], kCodeLengthCodes, 5, + &code_length_bitdepth[0]); + ConvertBitDepthsToSymbols(code_length_bitdepth, kCodeLengthCodes, + &code_length_bitdepth_symbols[0]); + + // Now, we have all the data, let's start storing it + StoreHuffmanTreeOfHuffmanTreeToBitMask(num_codes, code_length_bitdepth, + writer); + + if (num_codes == 1) { + code_length_bitdepth[code] = 0; + } + + // Store the real huffman tree now. + StoreHuffmanTreeToBitMask(huffman_tree_size, huffman_tree, + huffman_tree_extra_bits, &code_length_bitdepth[0], + code_length_bitdepth_symbols, writer); +} + +} // namespace + +void BuildAndStoreHuffmanTree(const uint32_t* histogram, const size_t length, + uint8_t* depth, uint16_t* bits, + BitWriter* writer) { + size_t count = 0; + size_t s4[4] = {0}; + for (size_t i = 0; i < length; i++) { + if (histogram[i]) { + if (count < 4) { + s4[count] = i; + } else if (count > 4) { + break; + } + count++; + } + } + + size_t max_bits_counter = length - 1; + size_t max_bits = 0; + while (max_bits_counter) { + max_bits_counter >>= 1; + ++max_bits; + } + + if (count <= 1) { + // Output symbol bits and depths are initialized with 0, nothing to do. + writer->Write(4, 1); + writer->Write(max_bits, s4[0]); + return; + } + + CreateHuffmanTree(histogram, length, 15, depth); + ConvertBitDepthsToSymbols(depth, length, bits); + + if (count <= 4) { + StoreSimpleHuffmanTree(depth, s4, count, max_bits, writer); + } else { + StoreHuffmanTree(depth, length, writer); + } +} + +} // namespace jxl |