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/*
* Copyright (c) 2016 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.
*/
#include "modules/rtp_rtcp/source/rtcp_packet/tmmb_item.h"
#include <cstdint>
#include "modules/rtp_rtcp/source/byte_io.h"
#include "rtc_base/checks.h"
#include "rtc_base/logging.h"
namespace webrtc {
namespace rtcp {
TmmbItem::TmmbItem(uint32_t ssrc, uint64_t bitrate_bps, uint16_t overhead)
: ssrc_(ssrc), bitrate_bps_(bitrate_bps), packet_overhead_(overhead) {
RTC_DCHECK_LE(overhead, 0x1ffu);
}
// 0 1 2 3
// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// 0 | SSRC |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// 4 | MxTBR Exp | MxTBR Mantissa |Measured Overhead|
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
bool TmmbItem::Parse(const uint8_t* buffer) {
ssrc_ = ByteReader<uint32_t>::ReadBigEndian(&buffer[0]);
// Read 4 bytes into 1 block.
uint32_t compact = ByteReader<uint32_t>::ReadBigEndian(&buffer[4]);
// Split 1 block into 3 components.
uint8_t exponent = compact >> 26; // 6 bits.
uint64_t mantissa = (compact >> 9) & 0x1ffff; // 17 bits.
uint16_t overhead = compact & 0x1ff; // 9 bits.
// Combine 3 components into 2 values.
bitrate_bps_ = (mantissa << exponent);
bool shift_overflow = (bitrate_bps_ >> exponent) != mantissa;
if (shift_overflow) {
RTC_LOG(LS_ERROR) << "Invalid tmmb bitrate value : " << mantissa << "*2^"
<< static_cast<int>(exponent);
return false;
}
packet_overhead_ = overhead;
return true;
}
void TmmbItem::Create(uint8_t* buffer) const {
constexpr uint64_t kMaxMantissa = 0x1ffff; // 17 bits.
uint64_t mantissa = bitrate_bps_;
uint32_t exponent = 0;
while (mantissa > kMaxMantissa) {
mantissa >>= 1;
++exponent;
}
ByteWriter<uint32_t>::WriteBigEndian(&buffer[0], ssrc_);
uint32_t compact = (exponent << 26) | (mantissa << 9) | packet_overhead_;
ByteWriter<uint32_t>::WriteBigEndian(&buffer[4], compact);
}
void TmmbItem::set_packet_overhead(uint16_t overhead) {
RTC_DCHECK_LE(overhead, 0x1ffu);
packet_overhead_ = overhead;
}
} // namespace rtcp
} // namespace webrtc
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