evaluate sequence numbers using standard method

protocols/sacn/receiver.cpp

@@ -26,8 +26,6 @@
 #include "receiver.h"
 #include "config.h"
 
-#include <limits>
-
 namespace sACN {
 
 /**
@@ -226,29 +224,22 @@ void Receiver::dataFrameHandler(ACN::PDU::Message<DATA::Pdu> frame) {
   if (source->sync_address != 0)
       subscribe(source->sync_address);
 
-  /// > \cite sACN 6.2.5 E1.31 Data Packet: Sequence Number
+  /// > \cite sACN 6.7.2 Sequence Numbering
   /// >
-  /// > In a routed network environment it is possible for packets to be
-  /// > received in a different order to the one in which they were sent. The
-  /// > sequence number allows receivers or diagnostic equipment to detect out
-  /// > of sequence or lost packets.
-  /// Assume that sources transmitting a sequence number of 0 do not support
-  /// sequencing.
-  if (source->sequence_number != 0 && universe->provenance())
-    {
-      auto seq = source->sequence_number;
-      auto old = universe->provenance()->sequence_number;
-      auto hasWrapped = [seq, old] () {
-          auto threshold = std::numeric_limits<typeof(old)>::max() * 0.9;
-          if (seq < old && old > threshold)
-            return true;
-          return false;
-        };
-      if (seq != old + 1)
-        ; // missed packet!
-      if (seq <= old && !hasWrapped())
-        return; // out of sequence packet!
-    }
+  /// > Having first received a packet with sequence number A,
+  auto a = universe->provenance()->sequence_number;
+  /// > a second packet with sequence number B arrives.
+  auto b = source->sequence_number;
+  /// > If, using signed 8-bit binary arithmetic, B - A
+  int8_t dif = b - a;
+  /// > is less than or equal to 0, but greater than -20,
+  if (dif <= 0 && dif > -20)
+  /// > then the packet containing sequence number B shall be deemed out of
+  /// > sequence and discarded.
+  /// Tolerate out-of-spec sources transmitting 0s instead of a sequence number.
+    if (!(a == 0 && b == 0))
+      return;
+
 
   // PDU data will be a block of DMP
   auto block = static_cast<ACN::PDU::Block<ACN::DMP::Pdu>*>(frame->data());

protocols/sacn/universe.cpp

@@ -31,6 +31,7 @@ namespace sACN {
  */
 Universe::Universe()
     : DMX::Universe(E131_NETWORK_DATA_LOSS_TIMEOUT)
+    , provenance_(std::shared_ptr<DATA::data_header>(new DATA::data_header()))
 {
 }