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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.
#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 <cstddef>
#include <cstdint>
#include <vector>
#include "lib/jxl/ans_params.h"
#include "lib/jxl/dec_ans.h"
#include "lib/jxl/enc_ans_params.h"
#include "lib/jxl/enc_bit_writer.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_;
};
static const int kNumFixedHistograms = 1;
struct EntropyEncodingData {
std::vector<std::vector<ANSEncSymbolInfo>> encoding_info;
bool use_prefix_code;
std::vector<HybridUintConfig> uint_config;
LZ77Params lz77;
std::vector<BitWriter> encoded_histograms;
};
// Integer to be encoded by an entropy coder, either ANS or Huffman.
struct Token {
Token() = default;
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);
// Writes the context map to the bitstream and concatenates the individual
// histogram bistreams in codes.encoded_histograms. Used in streaming mode.
void EncodeHistograms(const std::vector<uint8_t>& context_map,
const EntropyEncodingData& codes, BitWriter* writer,
size_t layer, AuxOut* aux_out);
// 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, size_t context_offset,
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,
size_t context_offset, 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_
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