+
+CongestionControl::CongestionControl()
+// I know, I know, it's an estimate (about 20 for IPv4, 48 for IPv6)
+: packet_overhead(20)
+// only sample every eighth packet for measuring RTT
+, sample_skip(8)
+, packets_lost(0)
+, packets_received(0)
+, packet_loss(0.0f)
+, stamp_cursor(15)
+, stamp_last(0)
+, rtt(64.0f)
+, next_sample(1000)
+, tx_bytes(0)
+, rx_bytes(0)
+, tx_kbps(0.0f)
+, rx_kbps(0.0f) {
+ Uint32 now = SDL_GetTicks();
+ for (Uint32 &s : stamps) {
+ s = now;
+ }
+ next_sample += now;
+}
+
+void CongestionControl::PacketSent(uint16_t seq) noexcept {
+ if (!SamplePacket(seq)) {
+ return;
+ }
+ stamp_cursor = (stamp_cursor + 1) % 16;
+ stamps[stamp_cursor] = SDL_GetTicks();
+ stamp_last = seq;
+}
+
+void CongestionControl::PacketLost(uint16_t seq) noexcept {
+ ++packets_lost;
+ UpdatePacketLoss();
+ UpdateRTT(seq);
+}
+
+void CongestionControl::PacketReceived(uint16_t seq) noexcept {
+ ++packets_received;
+ UpdatePacketLoss();
+ UpdateRTT(seq);
+}
+
+void CongestionControl::UpdatePacketLoss() noexcept {
+ unsigned int packets_total = packets_lost + packets_received;
+ if (packets_total >= 256) {
+ packet_loss = float(packets_lost) / float(packets_total);
+ packets_lost = 0;
+ packets_received = 0;
+ }
+}
+
+void CongestionControl::UpdateRTT(std::uint16_t seq) noexcept {
+ if (!SamplePacket(seq)) return;
+ int diff = HeadDiff(seq);
+ if (diff > 0 || diff < -15) {
+ // packet outside observed time frame
+ return;
+ }
+ int cur_rtt = SDL_GetTicks() - stamps[(stamp_cursor + diff + 16) % 16];
+ rtt += (cur_rtt - rtt) * 0.1f;
+}
+
+bool CongestionControl::SamplePacket(std::uint16_t seq) const noexcept {
+ return seq % sample_skip == 0;
+}
+
+int CongestionControl::HeadDiff(std::uint16_t seq) const noexcept {
+ int16_t diff = int16_t(seq) - int16_t(stamp_last);
+ return diff / sample_skip;
+}
+
+void CongestionControl::PacketIn(const UDPpacket &pack) noexcept {
+ rx_bytes += pack.len + packet_overhead;
+ UpdateStats();
+}
+
+void CongestionControl::PacketOut(const UDPpacket &pack) noexcept {
+ tx_bytes += pack.len + packet_overhead;
+ UpdateStats();
+}
+
+void CongestionControl::UpdateStats() noexcept {
+ Uint32 now = SDL_GetTicks();
+ if (now >= next_sample) {
+ tx_kbps = float(tx_bytes) * (1.0f / 1024.0f);
+ rx_kbps = float(rx_bytes) * (1.0f / 1024.0f);
+ tx_bytes = 0;
+ rx_bytes = 0;
+ next_sample += 1000;
+ }
+}
+
+