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Diffstat (limited to 'third_party/jpeg-xl/lib/jxl/enc_ans.h')
| -rw-r--r-- | third_party/jpeg-xl/lib/jxl/enc_ans.h | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/third_party/jpeg-xl/lib/jxl/enc_ans.h b/third_party/jpeg-xl/lib/jxl/enc_ans.h new file mode 100644 index 0000000000..a4afb19b4e --- /dev/null +++ b/third_party/jpeg-xl/lib/jxl/enc_ans.h @@ -0,0 +1,143 @@ +// 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. + +#ifndef LIB_JXL_ENC_ANS_H_ +#define LIB_JXL_ENC_ANS_H_ + +// Library to encode the ANS population counts to the bit-stream and encode +// symbols based on the respective distributions. + +#include <stddef.h> +#include <stdint.h> +#include <stdio.h> +#include <stdlib.h> +#include <string.h> + +#include <algorithm> +#include <vector> + +#include "lib/jxl/ans_common.h" +#include "lib/jxl/ans_params.h" +#include "lib/jxl/base/compiler_specific.h" +#include "lib/jxl/base/status.h" +#include "lib/jxl/dec_ans.h" +#include "lib/jxl/enc_ans_params.h" +#include "lib/jxl/enc_bit_writer.h" +#include "lib/jxl/huffman_table.h" + +namespace jxl { + +struct AuxOut; + +#define USE_MULT_BY_RECIPROCAL + +// precision must be equal to: #bits(state_) + #bits(freq) +#define RECIPROCAL_PRECISION (32 + ANS_LOG_TAB_SIZE) + +// Data structure representing one element of the encoding table built +// from a distribution. +// TODO(veluca): split this up, or use an union. +struct ANSEncSymbolInfo { + // ANS + uint16_t freq_; + std::vector<uint16_t> reverse_map_; +#ifdef USE_MULT_BY_RECIPROCAL + uint64_t ifreq_; +#endif + // Prefix coding. + uint8_t depth; + uint16_t bits; +}; + +class ANSCoder { + public: + ANSCoder() : state_(ANS_SIGNATURE << 16) {} + + uint32_t PutSymbol(const ANSEncSymbolInfo& t, uint8_t* nbits) { + uint32_t bits = 0; + *nbits = 0; + if ((state_ >> (32 - ANS_LOG_TAB_SIZE)) >= t.freq_) { + bits = state_ & 0xffff; + state_ >>= 16; + *nbits = 16; + } +#ifdef USE_MULT_BY_RECIPROCAL + // We use mult-by-reciprocal trick, but that requires 64b calc. + const uint32_t v = (state_ * t.ifreq_) >> RECIPROCAL_PRECISION; + const uint32_t offset = t.reverse_map_[state_ - v * t.freq_]; + state_ = (v << ANS_LOG_TAB_SIZE) + offset; +#else + state_ = ((state_ / t.freq_) << ANS_LOG_TAB_SIZE) + + t.reverse_map_[state_ % t.freq_]; +#endif + return bits; + } + + uint32_t GetState() const { return state_; } + + private: + uint32_t state_; +}; + +// RebalanceHistogram requires a signed type. +using ANSHistBin = int32_t; + +struct EntropyEncodingData { + std::vector<std::vector<ANSEncSymbolInfo>> encoding_info; + bool use_prefix_code; + std::vector<HybridUintConfig> uint_config; + LZ77Params lz77; +}; + +// Integer to be encoded by an entropy coder, either ANS or Huffman. +struct Token { + Token() {} + Token(uint32_t c, uint32_t value) + : is_lz77_length(false), context(c), value(value) {} + uint32_t is_lz77_length : 1; + uint32_t context : 31; + uint32_t value; +}; + +// Returns an estimate of the number of bits required to encode the given +// histogram (header bits plus data bits). +float ANSPopulationCost(const ANSHistBin* data, size_t alphabet_size); + +// Apply context clustering, compute histograms and encode them. Returns an +// estimate of the total bits used for encoding the stream. If `writer` == +// nullptr, the bit estimate will not take into account the context map (which +// does not get written if `num_contexts` == 1). +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); + +// Write the tokens to a string. +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); + +// Same as above, but assumes allotment created by caller. +size_t WriteTokens(const std::vector<Token>& tokens, + const EntropyEncodingData& codes, + const std::vector<uint8_t>& context_map, BitWriter* writer); + +// Exposed for tests; to be used with Writer=BitWriter only. +template <typename Writer> +void EncodeUintConfigs(const std::vector<HybridUintConfig>& uint_config, + Writer* writer, size_t log_alpha_size); +extern template void EncodeUintConfigs(const std::vector<HybridUintConfig>&, + BitWriter*, size_t); + +// Globally set the option to create fuzzer-friendly ANS streams. Negatively +// impacts compression. Not thread-safe. +void SetANSFuzzerFriendly(bool ans_fuzzer_friendly); +} // namespace jxl + +#endif // LIB_JXL_ENC_ANS_H_ |