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Refactor FEC code to use COW buffers

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This refactoring helps to reduce unnecessary memcpy calls on the receive
side.

This CL replaces
|uint8 data[IP_PACKET_SIZE]| with |rtc::CopyOnWriteBuffer data| in Packet class,
removes |length| field there, and does necessary changes.

This is a reland of these two CLs with fixes:
https://webrtc-review.googlesource.com/c/src/+/144942
https://webrtc-review.googlesource.com/c/src/+/144881

Bug: webrtc:10750
Change-Id: I76f6dee5a57ade59942ea2822ca4737edfe6438b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/145332
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Stefan Holmer <stefan@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29035}
This commit is contained in:
Ilya Nikolaevskiy
2019-09-02 13:58:49 +02:00
committed by Commit Bot
parent a66395e72f
commit eec5fff4df
25 changed files with 357 additions and 328 deletions
Download Patch File Download Diff File Expand all files Collapse all files

30
modules/rtp_rtcp/source/ulpfec_header_reader_writer.cc
View File

@ -57,24 +57,27 @@ UlpfecHeaderReader::~UlpfecHeaderReader() = default;
bool UlpfecHeaderReader::ReadFecHeader(
ForwardErrorCorrection::ReceivedFecPacket* fec_packet) const {
bool l_bit = (fec_packet->pkt->data[0] & 0x40) != 0u;
uint8_t* data = fec_packet->pkt->data.data();
if (fec_packet->pkt->data.size() < kPacketMaskOffset) {
return false; // Truncated packet.
}
bool l_bit = (data[0] & 0x40) != 0u;
size_t packet_mask_size =
l_bit ? kUlpfecPacketMaskSizeLBitSet : kUlpfecPacketMaskSizeLBitClear;
fec_packet->fec_header_size = UlpfecHeaderSize(packet_mask_size);
uint16_t seq_num_base =
ByteReader<uint16_t>::ReadBigEndian(&fec_packet->pkt->data[2]);
uint16_t seq_num_base = ByteReader<uint16_t>::ReadBigEndian(&data[2]);
fec_packet->protected_ssrc = fec_packet->ssrc; // Due to RED.
fec_packet->seq_num_base = seq_num_base;
fec_packet->packet_mask_offset = kPacketMaskOffset;
fec_packet->packet_mask_size = packet_mask_size;
fec_packet->protection_length =
ByteReader<uint16_t>::ReadBigEndian(&fec_packet->pkt->data[10]);
ByteReader<uint16_t>::ReadBigEndian(&data[10]);
// Store length recovery field in temporary location in header.
// This makes the header "compatible" with the corresponding
// FlexFEC location of the length recovery field, thus simplifying
// the XORing operations.
memcpy(&fec_packet->pkt->data[2], &fec_packet->pkt->data[8], 2);
memcpy(&data[2], &data[8], 2);
return true;
}
@ -105,28 +108,29 @@ void UlpfecHeaderWriter::FinalizeFecHeader(
const uint8_t* packet_mask,
size_t packet_mask_size,
ForwardErrorCorrection::Packet* fec_packet) const {
uint8_t* data = fec_packet->data.data();
// Set E bit to zero.
fec_packet->data[0] &= 0x7f;
data[0] &= 0x7f;
// Set L bit based on packet mask size. (Note that the packet mask
// can only take on two discrete values.)
bool l_bit = (packet_mask_size == kUlpfecPacketMaskSizeLBitSet);
if (l_bit) {
fec_packet->data[0] |= 0x40; // Set the L bit.
data[0] |= 0x40; // Set the L bit.
} else {
RTC_DCHECK_EQ(packet_mask_size, kUlpfecPacketMaskSizeLBitClear);
fec_packet->data[0] &= 0xbf; // Clear the L bit.
data[0] &= 0xbf; // Clear the L bit.
}
// Copy length recovery field from temporary location.
memcpy(&fec_packet->data[8], &fec_packet->data[2], 2);
memcpy(&data[8], &data[2], 2);
// Write sequence number base.
ByteWriter<uint16_t>::WriteBigEndian(&fec_packet->data[2], seq_num_base);
ByteWriter<uint16_t>::WriteBigEndian(&data[2], seq_num_base);
// Protection length is set to entire packet. (This is not
// required in general.)
const size_t fec_header_size = FecHeaderSize(packet_mask_size);
ByteWriter<uint16_t>::WriteBigEndian(&fec_packet->data[10],
fec_packet->length - fec_header_size);
ByteWriter<uint16_t>::WriteBigEndian(
&data[10], fec_packet->data.size() - fec_header_size);
// Copy the packet mask.
memcpy(&fec_packet->data[12], packet_mask, packet_mask_size);
memcpy(&data[12], packet_mask, packet_mask_size);
}
} // namespace webrtc