Update header formatterts to FlexFEC draft 03.

webrtc/modules/rtp_rtcp/source/flexfec_header_reader_writer.cc

 /*
  *  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.
  */
 
@@ skipping 67 matching lines @@
 FlexfecHeaderReader::~FlexfecHeaderReader() = default;
 
 // TODO(brandtr): Update this function when we support flexible masks,
 // retransmissions, and/or several protected SSRCs.
 bool FlexfecHeaderReader::ReadFecHeader(
     ForwardErrorCorrection::ReceivedFecPacket* fec_packet) const {
   if (fec_packet->pkt->length <= kBaseHeaderSize + kStreamSpecificHeaderSize) {
     LOG(LS_WARNING) << "Discarding truncated FlexFEC packet.";
     return false;
   }
-  bool f_bit = (fec_packet->pkt->data[0] & 0x80) != 0;
+  bool r_bit = (fec_packet->pkt->data[0] & 0x80) != 0;
+  if (r_bit) {
+    LOG(LS_INFO) << "FlexFEC packet with retransmission bit set. We do not yet "
+                    "support this, thus discarding the packet.";
+    return false;
+  }
+  bool f_bit = (fec_packet->pkt->data[0] & 0x40) != 0;
   if (f_bit) {
     LOG(LS_INFO) << "FlexFEC packet with inflexible generator matrix. We do "
                     "not yet support this, thus discarding packet.";
     return false;
   }
-  bool r_bit = (fec_packet->pkt->data[0] & 0x40) != 0;
-  if (r_bit) {
-    LOG(LS_INFO) << "FlexFEC packet with retransmission bit set. We do not yet "
-                    "support this, thus discarding the packet.";
-    return false;
-  }
   uint8_t ssrc_count =
       ByteReader<uint8_t>::ReadBigEndian(&fec_packet->pkt->data[8]);
   if (ssrc_count != 1) {
     LOG(LS_INFO) << "FlexFEC packet protecting multiple media SSRCs. We do not "
                     "yet support this, thus discarding packet.";
     return false;
   }
   uint32_t protected_ssrc =
       ByteReader<uint32_t>::ReadBigEndian(&fec_packet->pkt->data[12]);
   uint16_t seq_num_base =
@@ skipping 130 matching lines @@
 // writing in space that is intended for the header.
 //
 // TODO(brandtr): Update this function when we support offset-based masks,
 // retransmissions, and protecting multiple SSRCs.
 void FlexfecHeaderWriter::FinalizeFecHeader(
     uint32_t media_ssrc,
     uint16_t seq_num_base,
     const uint8_t* packet_mask,
     size_t packet_mask_size,
     ForwardErrorCorrection::Packet* fec_packet) const {
-  fec_packet->data[0] &= 0x7f;  // Clear F bit.
-  fec_packet->data[0] &= 0xbf;  // Clear R bit.
+  fec_packet->data[0] &= 0x7f;  // Clear R bit.
+  fec_packet->data[0] &= 0xbf;  // Clear F bit.
   ByteWriter<uint8_t>::WriteBigEndian(&fec_packet->data[8], kSsrcCount);
   ByteWriter<uint32_t, 3>::WriteBigEndian(&fec_packet->data[9], kReservedBits);
   ByteWriter<uint32_t>::WriteBigEndian(&fec_packet->data[12], media_ssrc);
   ByteWriter<uint16_t>::WriteBigEndian(&fec_packet->data[16], seq_num_base);
   // Adapt ULPFEC packet mask to FlexFEC header.
   //
   // We treat the mask parts as unsigned integers with host order endianness
   // in order to simplify the bit shifting between bytes.
   uint8_t* const written_packet_mask = fec_packet->data + kPacketMaskOffset;
   if (packet_mask_size == kUlpfecPacketMaskSizeLBitSet) {
@@ skipping 40 matching lines @@
       written_packet_mask[2] |= 0x80;          // Set K-bit 1.
       written_packet_mask[2] |= 0x40;          // Set bit 15.
     }
   } else {
     RTC_NOTREACHED() << "Incorrect packet mask size: " << packet_mask_size
                      << ".";
   }
 }
 
 }  // namespace webrtc