| /* |
| * Copyright 2019 The libgav1 Authors |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #ifndef LIBGAV1_SRC_UTILS_ENTROPY_DECODER_H_ |
| #define LIBGAV1_SRC_UTILS_ENTROPY_DECODER_H_ |
| |
| #include <cstddef> |
| #include <cstdint> |
| |
| #include "src/utils/bit_reader.h" |
| #include "src/utils/compiler_attributes.h" |
| |
| namespace libgav1 { |
| |
| class DaalaBitReader : public BitReader { |
| public: |
| DaalaBitReader(const uint8_t* data, size_t size, bool allow_update_cdf); |
| ~DaalaBitReader() override = default; |
| |
| // Move only. |
| DaalaBitReader(DaalaBitReader&& rhs) noexcept; |
| DaalaBitReader& operator=(DaalaBitReader&& rhs) noexcept; |
| |
| int ReadBit() final; |
| int64_t ReadLiteral(int num_bits) override; |
| // ReadSymbol() calls for which the |symbol_count| is only known at runtime |
| // will use this variant. |
| int ReadSymbol(uint16_t* cdf, int symbol_count); |
| // ReadSymbol() calls for which the |symbol_count| is equal to 2 (boolean |
| // symbols) will use this variant. |
| bool ReadSymbol(uint16_t* cdf); |
| bool ReadSymbolWithoutCdfUpdate(uint16_t* cdf); |
| // Use either linear search or binary search for decoding the symbol depending |
| // on |symbol_count|. ReadSymbol calls for which the |symbol_count| is known |
| // at compile time will use this variant. |
| template <int symbol_count> |
| int ReadSymbol(uint16_t* cdf); |
| |
| private: |
| // WindowSize must be an unsigned integer type with at least 32 bits. Use the |
| // largest type with fast arithmetic. size_t should meet these requirements. |
| static_assert(sizeof(size_t) == sizeof(void*), ""); |
| using WindowSize = size_t; |
| static constexpr uint32_t kWindowSize = |
| static_cast<uint32_t>(sizeof(WindowSize)) * 8; |
| static_assert(kWindowSize >= 32, ""); |
| |
| // Reads a symbol using the |cdf| table which contains the probabilities of |
| // each symbol. On a high level, this function does the following: |
| // 1) Scale the |cdf| values. |
| // 2) Find the index in the |cdf| array where the scaled CDF value crosses |
| // the modified |window_diff_| threshold. |
| // 3) That index is the symbol that has been decoded. |
| // 4) Update |window_diff_| and |values_in_range_| based on the symbol that |
| // has been decoded. |
| inline int ReadSymbolImpl(const uint16_t* cdf, int symbol_count); |
| // Similar to ReadSymbolImpl but it uses binary search to perform step 2 in |
| // the comment above. As of now, this function is called when |symbol_count| |
| // is greater than or equal to 8. |
| inline int ReadSymbolImplBinarySearch(const uint16_t* cdf, int symbol_count); |
| // Specialized implementation of ReadSymbolImpl based on the fact that |
| // symbol_count == 2. |
| inline int ReadSymbolImpl(const uint16_t* cdf); |
| // ReadSymbolN is a specialization of ReadSymbol for symbol_count == N. |
| int ReadSymbol4(uint16_t* cdf); |
| // ReadSymbolImplN is a specialization of ReadSymbolImpl for |
| // symbol_count == N. |
| LIBGAV1_ALWAYS_INLINE int ReadSymbolImpl8(const uint16_t* cdf); |
| inline void PopulateBits(); |
| // Normalizes the range so that 32768 <= |values_in_range_| < 65536. Also |
| // calls PopulateBits() if necessary. |
| inline void NormalizeRange(); |
| |
| const uint8_t* const data_; |
| const size_t size_; |
| size_t data_index_; |
| const bool allow_update_cdf_; |
| // Number of bits of data in the current value. |
| int bits_; |
| // Number of values in the current range. Declared as uint32_t for better |
| // performance but only the lower 16 bits are used. |
| uint32_t values_in_range_; |
| // The difference between the high end of the current range and the coded |
| // value minus 1. The 16 most significant bits of this variable is used to |
| // decode the next symbol. It is filled in whenever |bits_| is less than 0. |
| WindowSize window_diff_; |
| }; |
| |
| } // namespace libgav1 |
| |
| #endif // LIBGAV1_SRC_UTILS_ENTROPY_DECODER_H_ |