/* * Copyright 2015 The WebRTC 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 in the root of the source * tree. An additional intellectual property rights grant can be found * in the file PATENTS. All contributing project authors may * be found in the AUTHORS file in the root of the source tree. */ #ifndef RTC_BASE_BIT_BUFFER_H_ #define RTC_BASE_BIT_BUFFER_H_ #include <stddef.h> // For size_t. #include <stdint.h> // For integer types. #include "absl/strings/string_view.h" #include "api/units/data_size.h" namespace rtc { // A BitBuffer API for write operations. Supports symmetric write APIs to the // reading APIs of BitstreamReader. // Sizes/counts specify bits/bytes, for clarity. // Byte order is assumed big-endian/network. class BitBufferWriter { public: static constexpr webrtc::DataSize kMaxLeb128Length = webrtc::DataSize::Bytes(10); // Constructs a bit buffer for the writable buffer of `bytes`. BitBufferWriter(uint8_t* bytes, size_t byte_count); BitBufferWriter(const BitBufferWriter&) = delete; BitBufferWriter& operator=(const BitBufferWriter&) = delete; // Gets the current offset, in bytes/bits, from the start of the buffer. The // bit offset is the offset into the current byte, in the range [0,7]. void GetCurrentOffset(size_t* out_byte_offset, size_t* out_bit_offset); // The remaining bits in the byte buffer. uint64_t RemainingBitCount() const; // Moves current position `byte_count` bytes forward. Returns false if // there aren't enough bytes left in the buffer. bool ConsumeBytes(size_t byte_count); // Moves current position `bit_count` bits forward. Returns false if // there aren't enough bits left in the buffer. bool ConsumeBits(size_t bit_count); // Sets the current offset to the provied byte/bit offsets. The bit // offset is from the given byte, in the range [0,7]. bool Seek(size_t byte_offset, size_t bit_offset); // Writes byte-sized values from the buffer. Returns false if there isn't // enough data left for the specified type. bool WriteUInt8(uint8_t val); bool WriteUInt16(uint16_t val); bool WriteUInt32(uint32_t val); // Writes bit-sized values to the buffer. Returns false if there isn't enough // room left for the specified number of bits. bool WriteBits(uint64_t val, size_t bit_count); // Writes value in range [0, num_values - 1] // See ReadNonSymmetric documentation for the format, // Call SizeNonSymmetricBits to get number of bits needed to store the value. // Returns false if there isn't enough room left for the value. bool WriteNonSymmetric(uint32_t val, uint32_t num_values); // Returns number of bits required to store `val` with NonSymmetric encoding. static size_t SizeNonSymmetricBits(uint32_t val, uint32_t num_values); // Writes the exponential golomb encoded version of the supplied value. // Returns false if there isn't enough room left for the value. bool WriteExponentialGolomb(uint32_t val); // Writes the signed exponential golomb version of the supplied value. // Signed exponential golomb values are just the unsigned values mapped to the // sequence 0, 1, -1, 2, -2, etc. in order. bool WriteSignedExponentialGolomb(int32_t val); // Writes the Leb128 encoded value. bool WriteLeb128(uint64_t val); // Writes the string as bytes of data. bool WriteString(absl::string_view data); private: // The buffer, as a writable array. uint8_t* const writable_bytes_; // The total size of `bytes_`. const size_t byte_count_; // The current offset, in bytes, from the start of `bytes_`. size_t byte_offset_; // The current offset, in bits, into the current byte. size_t bit_offset_; }; } // namespace rtc #endif // RTC_BASE_BIT_BUFFER_H_