From 411412df7f20ff90bf28ec3f8cf259ceabc3384c Mon Sep 17 00:00:00 2001
From: ypothoma <thomas.pougetabadie@gmail.com>
Date: Tue, 24 Oct 2023 01:34:54 -0700
Subject: [PATCH] Reducing unnecessary allocations

---
 pkg/flexfec/flexfec_coverage.go |  9 +++++++++
 pkg/flexfec/flexfec_encoder.go  | 23 +++++++++++++++--------
 pkg/flexfec/util/bitarray.go    |  8 ++++++++
 3 files changed, 32 insertions(+), 8 deletions(-)

diff --git a/pkg/flexfec/flexfec_coverage.go b/pkg/flexfec/flexfec_coverage.go
index d3d27299..6fc6eb63 100644
--- a/pkg/flexfec/flexfec_coverage.go
+++ b/pkg/flexfec/flexfec_coverage.go
@@ -57,6 +57,15 @@ func NewCoverage(mediaPackets []rtp.Packet, numFecPackets uint32) *ProtectionCov
 	}
 }
 
+func (p *ProtectionCoverage) ResetCoverage() {
+	for i := uint32(0); i < MaxFecPackets; i++ {
+		for j := uint32(0); j < MaxMediaPackets; j++ {
+			p.packetMasks[i].SetBit(j, 0)
+		}
+	}
+
+}
+
 func (p *ProtectionCoverage) GetCoveredBy(fecPacketIndex uint32) *util.MediaPacketIterator {
 	coverage := make([]uint32, 0, p.numMediaPackets)
 	for mediaPacketIndex := uint32(0); mediaPacketIndex < p.numMediaPackets; mediaPacketIndex++ {
diff --git a/pkg/flexfec/flexfec_encoder.go b/pkg/flexfec/flexfec_encoder.go
index 3a784655..24c19048 100644
--- a/pkg/flexfec/flexfec_encoder.go
+++ b/pkg/flexfec/flexfec_encoder.go
@@ -14,6 +14,7 @@ type FlexFecEncoder struct {
 	baseSN      uint16
 	payloadType uint8
 	ssrc        uint32
+	coverage    *ProtectionCoverage
 }
 
 func NewFlexFecEncoder(baseSN uint16, payloadType uint8, ssrc uint32) *FlexFecEncoder {
@@ -21,6 +22,7 @@ func NewFlexFecEncoder(baseSN uint16, payloadType uint8, ssrc uint32) *FlexFecEn
 		baseSN:      baseSN,
 		payloadType: payloadType,
 		ssrc:        ssrc,
+		coverage:    nil,
 	}
 }
 
@@ -28,28 +30,33 @@ func NewFlexFecEncoder(baseSN uint16, payloadType uint8, ssrc uint32) *FlexFecEn
 // Encoding will be skipped if there are missing Media packets.
 func (flex *FlexFecEncoder) EncodeFec(mediaPackets []rtp.Packet, numFecPackets uint32) []rtp.Packet {
 	// Start by defining which FEC packets cover which media packets
-	coverage := NewCoverage(mediaPackets, numFecPackets)
+	// We transform mediaPackets array into a slice to avoid as many copies as possible.
+	if flex.coverage == nil {
+		flex.coverage = NewCoverage(mediaPackets[:], numFecPackets)
+	} else {
+		flex.coverage.ResetCoverage()
+	}
 
-	if coverage == nil {
+	if flex.coverage == nil {
 		return nil
 	}
 
 	// Generate FEC payloads
 	fecPackets := make([]rtp.Packet, numFecPackets)
 	for fecPacketIndex := uint32(0); fecPacketIndex < numFecPackets; fecPacketIndex++ {
-		fecPackets[fecPacketIndex] = flex.encodeFlexFecPacket(fecPacketIndex, coverage)
+		fecPackets[fecPacketIndex] = flex.encodeFlexFecPacket(fecPacketIndex)
 	}
 
 	return fecPackets
 }
 
-func (flex *FlexFecEncoder) encodeFlexFecPacket(fecPacketIndex uint32, coverage *ProtectionCoverage) rtp.Packet {
-	mediaPacketsIt := coverage.GetCoveredBy(fecPacketIndex)
+func (flex *FlexFecEncoder) encodeFlexFecPacket(fecPacketIndex uint32) rtp.Packet {
+	mediaPacketsIt := flex.coverage.GetCoveredBy(fecPacketIndex)
 	flexFecHeader := flex.encodeFlexFecHeader(
 		mediaPacketsIt,
-		coverage.ExtractMask1(fecPacketIndex),
-		coverage.ExtractMask2(fecPacketIndex),
-		coverage.ExtractMask3(fecPacketIndex),
+		flex.coverage.ExtractMask1(fecPacketIndex),
+		flex.coverage.ExtractMask2(fecPacketIndex),
+		flex.coverage.ExtractMask3(fecPacketIndex),
 	)
 	flexFecRepairPayload := flex.encodeFlexFecRepairPayload(mediaPacketsIt.Reset())
 
diff --git a/pkg/flexfec/util/bitarray.go b/pkg/flexfec/util/bitarray.go
index 4a4ee265..d0c82e31 100644
--- a/pkg/flexfec/util/bitarray.go
+++ b/pkg/flexfec/util/bitarray.go
@@ -20,7 +20,15 @@ func NewBitArray(sizeBits uint32) BitArray {
 }
 
 func (b *BitArray) SetBit(bitIndex uint32, bitValue uint32) {
+	byteIndex := bitIndex / 8
+	bitOffset := uint(bitIndex % 8)
 
+	// Set the specific bit to 1 using bitwise OR
+	if bitValue == 1 {
+		b.bytes[byteIndex] |= 1 << bitOffset
+	} else {
+		b.bytes[byteIndex] |= 0 << bitOffset
+	}
 }
 
 func (b *BitArray) GetBit(bitIndex uint32) uint8 {