f rewrite v2

Author: TheBlueMatt

lightning/src/routing/scoring.rs

@@ -1178,10 +1178,12 @@ impl<T: Time> Readable for ChannelLiquidity<T> {
 			(4, duration_since_epoch, required),
 		});
 		// On rust prior to 1.60 `Instant::duration_since` will panic if time goes backwards.
-		// Because we write `last_updated` as wallclock time when we were written and create an
-		// `Instant` which represents that wallclock time, we may hit that panic if wallclock time
-		// is before when we were written. Thus, we check if we'd end up with a time in the future
-		// and just use `now` instead to avoid panicking later.
+		// We write `last_updated` as wallclock time even though its ultimately an `Instant` (which
+		// is a time from a monotonic clock usually represented as an offset against boot time).
+		// Thus, we have to construct an `Instant` by subtracting the difference in wallclock time
+		// from the one that was written. However, because `Instant` can panic if we construct one
+		// in the future, we must handle wallclock time jumping backwards, which we do by simply
+		// using `Instant::now()` in that case.
 		let wall_clock_now = T::duration_since_epoch();
 		let now = T::now();
 		let last_updated = if wall_clock_now > duration_since_epoch {