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diff --git a/third_party/libwebrtc/rtc_base/bit_buffer.h b/third_party/libwebrtc/rtc_base/bit_buffer.h
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+/*
+ * 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.
+
+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:
+ // 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);
+
+ 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_