fix(stats): preserve signed per-packet IPDV in output

crates/irtt-stats/src/core.rs

@@ -175,29 +175,31 @@ impl CoreStats {
         let mut updates = Vec::new();
 
         for pair in self.ipdv_tracker.insert(sample) {
-            let Some(rtt_ipdv) = duration_from_non_negative_i128_ns(pair.rtt_ipdv_ns) else {
+            let rtt_magnitude_ns = pair.rtt_ipdv_ns.saturating_abs();
+            let send_magnitude_ns = pair.send_ipdv_ns.map(i128::saturating_abs);
+            let receive_magnitude_ns = pair.receive_ipdv_ns.map(i128::saturating_abs);
+            let Some(rtt_ipdv) = duration_from_non_negative_i128_ns(rtt_magnitude_ns) else {
                 continue;
             };
-            let send_ipdv = pair
-                .send_ipdv_ns
-                .and_then(duration_from_non_negative_i128_ns);
-            let receive_ipdv = pair
-                .receive_ipdv_ns
-                .and_then(duration_from_non_negative_i128_ns);
+            let send_ipdv = send_magnitude_ns.and_then(duration_from_non_negative_i128_ns);
+            let receive_ipdv = receive_magnitude_ns.and_then(duration_from_non_negative_i128_ns);
 
-            self.ipdv_round_trip.push_ns(pair.rtt_ipdv_ns);
+            self.ipdv_round_trip.push_ns(rtt_magnitude_ns);
 
-            if let Some(value) = pair.send_ipdv_ns {
+            if let Some(value) = send_magnitude_ns {
                 self.ipdv_send.push_ns(value);
             }
 
-            if let Some(value) = pair.receive_ipdv_ns {
+            if let Some(value) = receive_magnitude_ns {
                 self.ipdv_receive.push_ns(value);
             }
 
             updates.push(IpdvPairUpdate {
                 previous_seq: pair.previous_seq,
                 current_seq: pair.current_seq,
+                rtt_ipdv_ns: pair.rtt_ipdv_ns,
+                send_ipdv_ns: pair.send_ipdv_ns,
+                receive_ipdv_ns: pair.receive_ipdv_ns,
                 rtt_ipdv,
                 send_ipdv,
                 receive_ipdv,

crates/irtt-stats/src/ipdv.rs

@@ -89,9 +89,9 @@ impl IpdvTracker {
         Some(CompletedIpdvPair {
             previous_seq,
             current_seq,
-            rtt_ipdv_ns: abs_i128_ns(current.rtt_primary_ns - previous.rtt_primary_ns),
-            send_ipdv_ns: send_ipdv_ns(previous, current).map(abs_i128_ns),
-            receive_ipdv_ns: receive_ipdv_ns(previous, current).map(abs_i128_ns),
+            rtt_ipdv_ns: current.rtt_primary_ns - previous.rtt_primary_ns,
+            send_ipdv_ns: send_ipdv_ns(previous, current),
+            receive_ipdv_ns: receive_ipdv_ns(previous, current),
         })
     }
 }
@@ -161,10 +161,6 @@ fn duration_ns_i128(duration: Duration) -> i128 {
     i128::try_from(duration.as_nanos()).unwrap_or(i128::MAX)
 }
 
-fn abs_i128_ns(value: i128) -> i128 {
-    value.saturating_abs()
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;

crates/irtt-stats/src/lib.rs

@@ -520,6 +520,12 @@ pub struct IpdvPairUpdate {
     pub previous_seq: u32,
     /// Sequence number of the later reply in the adjacent pair.
     pub current_seq: u32,
+    /// Signed round-trip delay change (current minus previous) in nanoseconds.
+    pub rtt_ipdv_ns: i128,
+    /// Signed send-side delay change in nanoseconds, when available for both replies.
+    pub send_ipdv_ns: Option<i128>,
+    /// Signed receive-side delay change in nanoseconds, when available for both replies.
+    pub receive_ipdv_ns: Option<i128>,
     /// Absolute round-trip IPDV between the adjacent replies.
     pub rtt_ipdv: Duration,
     /// Absolute send-side IPDV when send one-way delay is available for both replies.