Store both min and max historical buckets in one, new, struct

In the coming commits we'll isolate historical bucket logic slightly
further, allowing us to cache some state. This is the first step
towards that, storing the historical liquidity information in a new
`HistoricalLiquidityTracker` rather than in the general
`ChannelLiquidity`.

Author: TheBlueMatt

lightning/src/routing/scoring.rs

@@ -790,8 +790,7 @@ struct ChannelLiquidity {
 	/// Upper channel liquidity bound in terms of an offset from the effective capacity.
 	max_liquidity_offset_msat: u64,
 
-	min_liquidity_offset_history: HistoricalBucketRangeTracker,
-	max_liquidity_offset_history: HistoricalBucketRangeTracker,
+	liquidity_history: HistoricalLiquidityTracker,
 
 	/// Time when either liquidity bound was last modified as an offset since the unix epoch.
 	last_updated: Duration,
@@ -982,8 +981,7 @@ impl ChannelLiquidity {
 		Self {
 			min_liquidity_offset_msat: 0,
 			max_liquidity_offset_msat: 0,
-			min_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
-			max_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
+			liquidity_history: HistoricalLiquidityTracker::new(),
 			last_updated,
 			offset_history_last_updated: last_updated,
 		}
@@ -994,22 +992,18 @@ impl ChannelLiquidity {
 	fn as_directed(
 		&self, source: &NodeId, target: &NodeId, capacity_msat: u64,
 	) -> DirectedChannelLiquidity<&u64, &HistoricalBucketRangeTracker, &Duration> {
-		let (min_liquidity_offset_msat, max_liquidity_offset_msat, min_liquidity_offset_history, max_liquidity_offset_history) =
-			if source < target {
-				(&self.min_liquidity_offset_msat, &self.max_liquidity_offset_msat,
-					&self.min_liquidity_offset_history, &self.max_liquidity_offset_history)
+		let source_less_than_target = source < target;
+		let (min_liquidity_offset_msat, max_liquidity_offset_msat) =
+			if source_less_than_target {
+				(&self.min_liquidity_offset_msat, &self.max_liquidity_offset_msat)
 			} else {
-				(&self.max_liquidity_offset_msat, &self.min_liquidity_offset_msat,
-					&self.max_liquidity_offset_history, &self.min_liquidity_offset_history)
+				(&self.max_liquidity_offset_msat, &self.min_liquidity_offset_msat)
 			};
 
 		DirectedChannelLiquidity {
 			min_liquidity_offset_msat,
 			max_liquidity_offset_msat,
-			liquidity_history: HistoricalMinMaxBuckets {
-				min_liquidity_offset_history,
-				max_liquidity_offset_history,
-			},
+			liquidity_history: self.liquidity_history.as_directed(source_less_than_target),
 			capacity_msat,
 			last_updated: &self.last_updated,
 			offset_history_last_updated: &self.offset_history_last_updated,
@@ -1021,22 +1015,18 @@ impl ChannelLiquidity {
 	fn as_directed_mut(
 		&mut self, source: &NodeId, target: &NodeId, capacity_msat: u64,
 	) -> DirectedChannelLiquidity<&mut u64, &mut HistoricalBucketRangeTracker, &mut Duration> {
-		let (min_liquidity_offset_msat, max_liquidity_offset_msat, min_liquidity_offset_history, max_liquidity_offset_history) =
-			if source < target {
-				(&mut self.min_liquidity_offset_msat, &mut self.max_liquidity_offset_msat,
-					&mut self.min_liquidity_offset_history, &mut self.max_liquidity_offset_history)
+		let source_less_than_target = source < target;
+		let (min_liquidity_offset_msat, max_liquidity_offset_msat) =
+			if source_less_than_target {
+				(&mut self.min_liquidity_offset_msat, &mut self.max_liquidity_offset_msat)
 			} else {
-				(&mut self.max_liquidity_offset_msat, &mut self.min_liquidity_offset_msat,
-					&mut self.max_liquidity_offset_history, &mut self.min_liquidity_offset_history)
+				(&mut self.max_liquidity_offset_msat, &mut self.min_liquidity_offset_msat)
 			};
 
 		DirectedChannelLiquidity {
 			min_liquidity_offset_msat,
 			max_liquidity_offset_msat,
-			liquidity_history: HistoricalMinMaxBuckets {
-				min_liquidity_offset_history,
-				max_liquidity_offset_history,
-			},
+			liquidity_history: self.liquidity_history.as_directed_mut(source_less_than_target),
 			capacity_msat,
 			last_updated: &mut self.last_updated,
 			offset_history_last_updated: &mut self.offset_history_last_updated,
@@ -1462,18 +1452,18 @@ impl<G: Deref<Target = NetworkGraph<L>>, L: Deref> ScoreUpdate for Probabilistic
 				let half_life = decay_params.historical_no_updates_half_life.as_secs_f64();
 				if half_life != 0.0 {
 					let divisor = powf64(2048.0, elapsed_time.as_secs_f64() / half_life) as u64;
-					for bucket in liquidity.min_liquidity_offset_history.buckets.iter_mut() {
+					for bucket in liquidity.liquidity_history.min_liquidity_offset_history.buckets.iter_mut() {
 						*bucket = ((*bucket as u64) * 1024 / divisor) as u16;
 					}
-					for bucket in liquidity.max_liquidity_offset_history.buckets.iter_mut() {
+					for bucket in liquidity.liquidity_history.max_liquidity_offset_history.buckets.iter_mut() {
 						*bucket = ((*bucket as u64) * 1024 / divisor) as u16;
 					}
 					liquidity.offset_history_last_updated = duration_since_epoch;
 				}
 			}
 			liquidity.min_liquidity_offset_msat != 0 || liquidity.max_liquidity_offset_msat != 0 ||
-				liquidity.min_liquidity_offset_history.buckets != [0; 32] ||
-				liquidity.max_liquidity_offset_history.buckets != [0; 32]
+				liquidity.liquidity_history.min_liquidity_offset_history.buckets != [0; 32] ||
+				liquidity.liquidity_history.max_liquidity_offset_history.buckets != [0; 32]
 		});
 	}
 }
@@ -1648,6 +1638,54 @@ mod bucketed_history {
 	impl_writeable_tlv_based!(HistoricalBucketRangeTracker, { (0, buckets, required) });
 	impl_writeable_tlv_based!(LegacyHistoricalBucketRangeTracker, { (0, buckets, required) });
 
+
+	#[derive(Clone, Copy)]
+	pub(super) struct HistoricalLiquidityTracker {
+		pub(super) min_liquidity_offset_history: HistoricalBucketRangeTracker,
+		pub(super) max_liquidity_offset_history: HistoricalBucketRangeTracker,
+	}
+
+	impl HistoricalLiquidityTracker {
+		pub(super) fn new() -> HistoricalLiquidityTracker {
+			HistoricalLiquidityTracker {
+				min_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
+				max_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
+			}
+		}
+
+		pub(super) fn from_min_max(
+			min_liquidity_offset_history: HistoricalBucketRangeTracker,
+			max_liquidity_offset_history: HistoricalBucketRangeTracker,
+		) -> HistoricalLiquidityTracker {
+			HistoricalLiquidityTracker {
+				min_liquidity_offset_history,
+				max_liquidity_offset_history,
+			}
+		}
+
+		pub(super) fn as_directed<'a>(&'a self, source_less_than_target: bool)
+		-> HistoricalMinMaxBuckets<&'a HistoricalBucketRangeTracker> {
+			let (min_liquidity_offset_history, max_liquidity_offset_history) =
+				if source_less_than_target {
+					(&self.min_liquidity_offset_history, &self.max_liquidity_offset_history)
+				} else {
+					(&self.max_liquidity_offset_history, &self.min_liquidity_offset_history)
+				};
+			HistoricalMinMaxBuckets { min_liquidity_offset_history, max_liquidity_offset_history }
+		}
+
+		pub(super) fn as_directed_mut<'a>(&'a mut self, source_less_than_target: bool)
+		-> HistoricalMinMaxBuckets<&'a mut HistoricalBucketRangeTracker> {
+			let (min_liquidity_offset_history, max_liquidity_offset_history) =
+				if source_less_than_target {
+					(&mut self.min_liquidity_offset_history, &mut self.max_liquidity_offset_history)
+				} else {
+					(&mut self.max_liquidity_offset_history, &mut self.min_liquidity_offset_history)
+				};
+			HistoricalMinMaxBuckets { min_liquidity_offset_history, max_liquidity_offset_history }
+		}
+	}
+
 	/// A set of buckets representing the history of where we've seen the minimum- and maximum-
 	/// liquidity bounds for a given channel.
 	pub(super) struct HistoricalMinMaxBuckets<D: Deref<Target = HistoricalBucketRangeTracker>> {
@@ -1745,7 +1783,7 @@ mod bucketed_history {
 		}
 	}
 }
-use bucketed_history::{LegacyHistoricalBucketRangeTracker, HistoricalBucketRangeTracker, HistoricalMinMaxBuckets};
+use bucketed_history::{LegacyHistoricalBucketRangeTracker, HistoricalBucketRangeTracker, HistoricalMinMaxBuckets, HistoricalLiquidityTracker};
 
 impl<G: Deref<Target = NetworkGraph<L>>, L: Deref> Writeable for ProbabilisticScorer<G, L> where L::Target: Logger {
 	#[inline]
@@ -1786,8 +1824,8 @@ impl Writeable for ChannelLiquidity {
 			(2, self.max_liquidity_offset_msat, required),
 			// 3 was the max_liquidity_offset_history in octile form
 			(4, self.last_updated, required),
-			(5, Some(self.min_liquidity_offset_history), option),
-			(7, Some(self.max_liquidity_offset_history), option),
+			(5, self.liquidity_history.min_liquidity_offset_history, required),
+			(7, self.liquidity_history.max_liquidity_offset_history, required),
 			(9, self.offset_history_last_updated, required),
 		});
 		Ok(())
@@ -1833,8 +1871,9 @@ impl Readable for ChannelLiquidity {
 		Ok(Self {
 			min_liquidity_offset_msat,
 			max_liquidity_offset_msat,
-			min_liquidity_offset_history: min_liquidity_offset_history.unwrap(),
-			max_liquidity_offset_history: max_liquidity_offset_history.unwrap(),
+			liquidity_history: HistoricalLiquidityTracker::from_min_max(
+				min_liquidity_offset_history.unwrap(), max_liquidity_offset_history.unwrap()
+			),
 			last_updated,
 			offset_history_last_updated: offset_history_last_updated.unwrap_or(last_updated),
 		})
@@ -1843,7 +1882,7 @@ impl Readable for ChannelLiquidity {
 
 #[cfg(test)]
 mod tests {
-	use super::{ChannelLiquidity, HistoricalBucketRangeTracker, ProbabilisticScoringFeeParameters, ProbabilisticScoringDecayParameters, ProbabilisticScorer};
+	use super::{ChannelLiquidity, HistoricalLiquidityTracker, ProbabilisticScoringFeeParameters, ProbabilisticScoringDecayParameters, ProbabilisticScorer};
 	use crate::blinded_path::BlindedHop;
 	use crate::util::config::UserConfig;
 
@@ -2016,15 +2055,13 @@ mod tests {
 				ChannelLiquidity {
 					min_liquidity_offset_msat: 700, max_liquidity_offset_msat: 100,
 					last_updated, offset_history_last_updated,
-					min_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
-					max_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
+					liquidity_history: HistoricalLiquidityTracker::new(),
 				})
 			.with_channel(43,
 				ChannelLiquidity {
 					min_liquidity_offset_msat: 700, max_liquidity_offset_msat: 100,
 					last_updated, offset_history_last_updated,
-					min_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
-					max_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
+					liquidity_history: HistoricalLiquidityTracker::new(),
 				});
 		let source = source_node_id();
 		let target = target_node_id();
@@ -2097,8 +2134,7 @@ mod tests {
 				ChannelLiquidity {
 					min_liquidity_offset_msat: 200, max_liquidity_offset_msat: 400,
 					last_updated, offset_history_last_updated,
-					min_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
-					max_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
+					liquidity_history: HistoricalLiquidityTracker::new(),
 				});
 		let source = source_node_id();
 		let target = target_node_id();
@@ -2158,8 +2194,7 @@ mod tests {
 				ChannelLiquidity {
 					min_liquidity_offset_msat: 200, max_liquidity_offset_msat: 400,
 					last_updated, offset_history_last_updated,
-					min_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
-					max_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
+					liquidity_history: HistoricalLiquidityTracker::new(),
 				});
 		let source = source_node_id();
 		let target = target_node_id();
@@ -2278,8 +2313,7 @@ mod tests {
 				ChannelLiquidity {
 					min_liquidity_offset_msat: 40, max_liquidity_offset_msat: 40,
 					last_updated, offset_history_last_updated,
-					min_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
-					max_liquidity_offset_history: HistoricalBucketRangeTracker::new(),
+					liquidity_history: HistoricalLiquidityTracker::new(),
 				});
 		let source = source_node_id();