f add reasons why the constants

Author: TheBlueMatt

lightning/src/routing/scoring.rs

@@ -455,6 +455,14 @@ impl HistoricalBucketRangeTracker {
 		//
 		// In total, this allows us to track data for the last 8,000 or so payments across a given
 		// channel.
+		//
+		// These constants are a balance - we try to fit in 2 bytes per bucket to reduce overhead,
+		// and need to balance having more bits in the decimal part (to ensure decay isn't too
+		// step-wise) with having too few bits in the mantissa, causing us to not store very many
+		// datapoints.
+		//
+		// The constants were picked experimentally, selecting a decay amount that restricts us
+		// from overflowing buckets without having to cap them manually.
 		debug_assert!(bucket < 8);
 		if let Some(v) = self.buckets.get_mut(bucket as usize) {
 			*v = v.saturating_add(32);