Line data    Source code

       1             : /*
       2             :  *  Copyright (c) 2016 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             : #include "webrtc/modules/rtp_rtcp/source/rtcp_packet/tmmb_item.h"
      12             : 
      13             : #include "webrtc/base/checks.h"
      14             : #include "webrtc/base/logging.h"
      15             : #include "webrtc/modules/rtp_rtcp/source/byte_io.h"
      16             : 
      17             : namespace webrtc {
      18             : namespace rtcp {
      19           0 : TmmbItem::TmmbItem(uint32_t ssrc, uint64_t bitrate_bps, uint16_t overhead)
      20           0 :     : ssrc_(ssrc), bitrate_bps_(bitrate_bps), packet_overhead_(overhead) {
      21           0 :   RTC_DCHECK_LE(overhead, 0x1ffu);
      22           0 : }
      23             : 
      24             : //    0                   1                   2                   3
      25             : //    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
      26             : //   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      27             : // 0 |                              SSRC                             |
      28             : //   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      29             : // 4 | MxTBR Exp |  MxTBR Mantissa                 |Measured Overhead|
      30             : //   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      31           0 : bool TmmbItem::Parse(const uint8_t* buffer) {
      32           0 :   ssrc_ = ByteReader<uint32_t>::ReadBigEndian(&buffer[0]);
      33             :   // Read 4 bytes into 1 block.
      34           0 :   uint32_t compact = ByteReader<uint32_t>::ReadBigEndian(&buffer[4]);
      35             :   // Split 1 block into 3 components.
      36           0 :   uint8_t exponent = compact >> 26;              // 6 bits.
      37           0 :   uint64_t mantissa = (compact >> 9) & 0x1ffff;  // 17 bits.
      38           0 :   uint16_t overhead = compact & 0x1ff;           // 9 bits.
      39             :   // Combine 3 components into 2 values.
      40           0 :   bitrate_bps_ = (mantissa << exponent);
      41             : 
      42           0 :   bool shift_overflow = (bitrate_bps_ >> exponent) != mantissa;
      43           0 :   if (shift_overflow) {
      44           0 :     LOG(LS_ERROR) << "Invalid tmmb bitrate value : " << mantissa
      45           0 :                   << "*2^" << static_cast<int>(exponent);
      46           0 :     return false;
      47             :   }
      48           0 :   packet_overhead_ = overhead;
      49           0 :   return true;
      50             : }
      51             : 
      52           0 : void TmmbItem::Create(uint8_t* buffer) const {
      53           0 :   constexpr uint64_t kMaxMantissa = 0x1ffff;  // 17 bits.
      54           0 :   uint64_t mantissa = bitrate_bps_;
      55           0 :   uint32_t exponent = 0;
      56           0 :   while (mantissa > kMaxMantissa) {
      57           0 :     mantissa >>= 1;
      58           0 :     ++exponent;
      59             :   }
      60             : 
      61           0 :   ByteWriter<uint32_t>::WriteBigEndian(&buffer[0], ssrc_);
      62           0 :   uint32_t compact = (exponent << 26) | (mantissa << 9) | packet_overhead_;
      63           0 :   ByteWriter<uint32_t>::WriteBigEndian(&buffer[4], compact);
      64           0 : }
      65             : 
      66           0 : void TmmbItem::set_packet_overhead(uint16_t overhead) {
      67           0 :   RTC_DCHECK_LE(overhead, 0x1ffu);
      68           0 :   packet_overhead_ = overhead;
      69           0 : }
      70             : }  // namespace rtcp
      71             : }  // namespace webrtc