1 /* 2 * Copyright 2015 The WebRTC Project Authors. All rights reserved. 3 * 4 * Use of this source code is governed by a BSD-style license 5 * that can be found in the LICENSE file in the root of the source 6 * tree. An additional intellectual property rights grant can be found 7 * in the file PATENTS. All contributing project authors may 8 * be found in the AUTHORS file in the root of the source tree. 9 */ 10 11 #ifndef RTC_BASE_BIT_BUFFER_H_ 12 #define RTC_BASE_BIT_BUFFER_H_ 13 14 #include <stddef.h> // For size_t. 15 #include <stdint.h> // For integer types. 16 17 namespace rtc { 18 19 // A BitBuffer API for write operations. Supports symmetric write APIs to the 20 // reading APIs of BitstreamReader. 21 // Sizes/counts specify bits/bytes, for clarity. 22 // Byte order is assumed big-endian/network. 23 class BitBufferWriter { 24 public: 25 // Constructs a bit buffer for the writable buffer of `bytes`. 26 BitBufferWriter(uint8_t* bytes, size_t byte_count); 27 28 BitBufferWriter(const BitBufferWriter&) = delete; 29 BitBufferWriter& operator=(const BitBufferWriter&) = delete; 30 31 // Gets the current offset, in bytes/bits, from the start of the buffer. The 32 // bit offset is the offset into the current byte, in the range [0,7]. 33 void GetCurrentOffset(size_t* out_byte_offset, size_t* out_bit_offset); 34 35 // The remaining bits in the byte buffer. 36 uint64_t RemainingBitCount() const; 37 38 // Moves current position `byte_count` bytes forward. Returns false if 39 // there aren't enough bytes left in the buffer. 40 bool ConsumeBytes(size_t byte_count); 41 // Moves current position `bit_count` bits forward. Returns false if 42 // there aren't enough bits left in the buffer. 43 bool ConsumeBits(size_t bit_count); 44 45 // Sets the current offset to the provied byte/bit offsets. The bit 46 // offset is from the given byte, in the range [0,7]. 47 bool Seek(size_t byte_offset, size_t bit_offset); 48 49 // Writes byte-sized values from the buffer. Returns false if there isn't 50 // enough data left for the specified type. 51 bool WriteUInt8(uint8_t val); 52 bool WriteUInt16(uint16_t val); 53 bool WriteUInt32(uint32_t val); 54 55 // Writes bit-sized values to the buffer. Returns false if there isn't enough 56 // room left for the specified number of bits. 57 bool WriteBits(uint64_t val, size_t bit_count); 58 59 // Writes value in range [0, num_values - 1] 60 // See ReadNonSymmetric documentation for the format, 61 // Call SizeNonSymmetricBits to get number of bits needed to store the value. 62 // Returns false if there isn't enough room left for the value. 63 bool WriteNonSymmetric(uint32_t val, uint32_t num_values); 64 // Returns number of bits required to store `val` with NonSymmetric encoding. 65 static size_t SizeNonSymmetricBits(uint32_t val, uint32_t num_values); 66 67 // Writes the exponential golomb encoded version of the supplied value. 68 // Returns false if there isn't enough room left for the value. 69 bool WriteExponentialGolomb(uint32_t val); 70 // Writes the signed exponential golomb version of the supplied value. 71 // Signed exponential golomb values are just the unsigned values mapped to the 72 // sequence 0, 1, -1, 2, -2, etc. in order. 73 bool WriteSignedExponentialGolomb(int32_t val); 74 75 private: 76 // The buffer, as a writable array. 77 uint8_t* const writable_bytes_; 78 // The total size of `bytes_`. 79 const size_t byte_count_; 80 // The current offset, in bytes, from the start of `bytes_`. 81 size_t byte_offset_; 82 // The current offset, in bits, into the current byte. 83 size_t bit_offset_; 84 }; 85 86 } // namespace rtc 87 88 #endif // RTC_BASE_BIT_BUFFER_H_ 89