text: /*
   *  Copyright (c) 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 WEBRTC_MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_NACK_H_
  #define WEBRTC_MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_NACK_H_
  
  #include <vector>
  
  #include "webrtc/modules/rtp_rtcp/source/rtcp_packet/rtpfb.h"
  #include "webrtc/rtc_base/basictypes.h"
  
  namespace webrtc {
  namespace rtcp {
  class CommonHeader;
  
  class Nack : public Rtpfb {
   public:
    static constexpr uint8_t kFeedbackMessageType = 1;
    Nack();
    ~Nack() override;
  
    // Parse assumes header is already parsed and validated.
    bool Parse(const CommonHeader& packet);
  
    void SetPacketIds(const uint16_t* nack_list, size_t length);
    const std::vector<uint16_t>& packet_ids() const { return packet_ids_; }
  
    size_t BlockLength() const override;
  
    bool Create(uint8_t* packet,
                size_t* index,
                size_t max_length,
                RtcpPacket::PacketReadyCallback* callback) const override;
  
   private:
    static constexpr size_t kNackItemLength = 4;
    struct PackedNack {
      uint16_t first_pid;
      uint16_t bitmask;
    };
  
    void Pack();    // Fills packed_ using packed_ids_. (used in SetPacketIds).
    void Unpack();  // Fills packet_ids_ using packed_. (used in Parse).
  
    std::vector<PackedNack> packed_;
    std::vector<uint16_t> packet_ids_;
  };
  
  }  // namespace rtcp
  }  // namespace webrtc
  #endif  // WEBRTC_MODULES_RTP_RTCP_SOURCE_RTCP_PACKET_NACK_H_
  