commit fb60796b642e6a0650afc88389f967a9a749984c
author Philipp Hancke <phancke@nvidia.com> Thu Feb 10 19:02:10 2022
committer WebRTC LUCI CQ <webrtc-scoped@luci-project-accounts.iam.gserviceaccount.com> Thu Jun 30 11:53:58 2022
tree dedd4a89760f65b0cf4a6f2561b85b5f33fcfe86
parent 42b163f2365f9ec68940ebd1367c03097ef8f324

fec: simplify fec generation

since the fec packets are initialized to 0 there is no need
to special-case the first packet since
  A XOR 0
is the identity operator.

BUG=None

Change-Id: I0cb55283ecdca06f8e3a7b5856ec1f9fbbad1ffb
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/251522
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37378}

modules/rtp_rtcp/source/forward_error_correction.cc

diff --git a/modules/rtp_rtcp/source/forward_error_correction.cc b/modules/rtp_rtcp/source/forward_error_correction.cc
index ed6a757..903d3e7 100644
--- a/modules/rtp_rtcp/source/forward_error_correction.cc
+++ b/modules/rtp_rtcp/source/forward_error_correction.cc
@@ -218,13 +218,11 @@
         ParseSequenceNumber((*media_packets_it)->data.data());
     while (media_packets_it != media_packets.end()) {
       Packet* const media_packet = media_packets_it->get();
-      const uint8_t* media_packet_data = media_packet->data.cdata();
       // Should `media_packet` be protected by `fec_packet`?
       if (packet_masks_[pkt_mask_idx] & (1 << (7 - media_pkt_idx))) {
         size_t media_payload_length =
             media_packet->data.size() - kRtpHeaderSize;
 
-        bool first_protected_packet = (fec_packet->data.size() == 0);
         size_t fec_packet_length = fec_header_size + media_payload_length;
         if (fec_packet_length > fec_packet->data.size()) {
           // Recall that XORing with zero (which the FEC packets are prefilled
@@ -232,26 +230,9 @@
           // still correct even though we expand the packet length here.
           fec_packet->data.SetSize(fec_packet_length);
         }
-        if (first_protected_packet) {
-          uint8_t* data = fec_packet->data.MutableData();
-          // Write P, X, CC, M, and PT recovery fields.
-          // Note that bits 0, 1, and 16 are overwritten in FinalizeFecHeaders.
-          memcpy(&data[0], &media_packet_data[0], 2);
-          // Write length recovery field. (This is a temporary location for
-          // ULPFEC.)
-          ByteWriter<uint16_t>::WriteBigEndian(&data[2], media_payload_length);
-          // Write timestamp recovery field.
-          memcpy(&data[4], &media_packet_data[4], 4);
-          // Write payload.
-          if (media_payload_length > 0) {
-            memcpy(&data[fec_header_size], &media_packet_data[kRtpHeaderSize],
-                   media_payload_length);
-          }
-        } else {
-          XorHeaders(*media_packet, fec_packet);
-          XorPayloads(*media_packet, media_payload_length, fec_header_size,
-                      fec_packet);
-        }
+        XorHeaders(*media_packet, fec_packet);
+        XorPayloads(*media_packet, media_payload_length, fec_header_size,
+                    fec_packet);
       }
       media_packets_it++;
       if (media_packets_it != media_packets.end()) {