From: Matt Corallo <git@bluematt.me>
Date: Tue, 12 Dec 2023 16:53:31 +0000 (+0000)
Subject: Move in-inner-scoring-loop if out to the top level
X-Git-Url: http://git.bitcoin.ninja/?a=commitdiff_plain;h=24083c10e7fafab279a6a74cc8aee30a695ef623;p=rust-lightning

Move in-inner-scoring-loop if out to the top level

When scoring channels, walking the historical buckets ends up being
the vast majority of our time. While LLVM is smart enough to pull
some conditionals out of the inner loop, we shouldn't make LLVM do
the work, and avoiding it can let us optimize the algorithm
somewhat in the coming commits.
---

diff --git a/lightning/src/routing/scoring.rs b/lightning/src/routing/scoring.rs
index a35315700..3460ce655 100644
--- a/lightning/src/routing/scoring.rs
+++ b/lightning/src/routing/scoring.rs
@@ -1837,18 +1837,30 @@ mod bucketed_history {
 
 			for (min_idx, min_bucket) in min_liquidity_offset_history_buckets.iter().enumerate().skip(1) {
 				let min_bucket_start_pos = BUCKET_START_POS[min_idx];
-				for (max_idx, max_bucket) in max_liquidity_offset_history_buckets.iter().enumerate().take(32 - min_idx) {
-					let max_bucket_end_pos = BUCKET_START_POS[32 - max_idx] - 1;
-					// Note that this multiply can only barely not overflow - two 16 bit ints plus
-					// 30 bits is 62 bits.
-					let bucket_prob_times_billion = (*min_bucket as u64) * (*max_bucket as u64)
-						* 1024 * 1024 * 1024 / total_valid_points_tracked;
-					if payment_pos >= max_bucket_end_pos {
-						// Success probability 0, the payment amount may be above the max liquidity
-						break;
-					} else if payment_pos < min_bucket_start_pos {
+				if payment_pos < min_bucket_start_pos {
+					for (max_idx, max_bucket) in max_liquidity_offset_history_buckets.iter().enumerate().take(32 - min_idx) {
+						let max_bucket_end_pos = BUCKET_START_POS[32 - max_idx] - 1;
+						// Note that this multiply can only barely not overflow - two 16 bit ints plus
+						// 30 bits is 62 bits.
+						let bucket_prob_times_billion = (*min_bucket as u64) * (*max_bucket as u64)
+							* 1024 * 1024 * 1024 / total_valid_points_tracked;
+						if payment_pos >= max_bucket_end_pos {
+							// Success probability 0, the payment amount may be above the max liquidity
+							break;
+						}
 						cumulative_success_prob_times_billion += bucket_prob_times_billion;
-					} else {
+					}
+				} else {
+					for (max_idx, max_bucket) in max_liquidity_offset_history_buckets.iter().enumerate().take(32 - min_idx) {
+						let max_bucket_end_pos = BUCKET_START_POS[32 - max_idx] - 1;
+						// Note that this multiply can only barely not overflow - two 16 bit ints plus
+						// 30 bits is 62 bits.
+						let bucket_prob_times_billion = (*min_bucket as u64) * (*max_bucket as u64)
+							* 1024 * 1024 * 1024 / total_valid_points_tracked;
+						if payment_pos >= max_bucket_end_pos {
+							// Success probability 0, the payment amount may be above the max liquidity
+							break;
+						}
 						let (numerator, denominator) = success_probability(payment_pos as u64,
 							min_bucket_start_pos as u64, max_bucket_end_pos as u64,
 							POSITION_TICKS as u64 - 1, params, true);