f O(N)

Author: valentinewallace

lightning/src/blinded_path/payment.rs

@@ -159,8 +159,7 @@ pub(super) fn compute_payinfo(
 	let mut curr_base_fee: u64 = 0;
 	let mut curr_prop_mil: u64 = 0;
 	let mut cltv_expiry_delta: u16 = 0;
-	let mut htlc_minimum_msat = payee_tlvs.payment_constraints.htlc_minimum_msat as u128;
-	for (idx, (_, tlvs)) in intermediate_nodes.iter().enumerate().rev() {
+	for (_, tlvs) in intermediate_nodes.iter().rev() {
 		// In the future, we'll want to take the intersection of all supported features for the
 		// `BlindedPayInfo`, but there are no features in that context right now.
 		if tlvs.features.requires_unknown_bits_from(&BlindedHopFeatures::empty()) { return Err(()) }
@@ -184,23 +183,24 @@ pub(super) fn compute_payinfo(
 			.ok_or(())?;
 
 		cltv_expiry_delta = cltv_expiry_delta.checked_add(tlvs.payment_relay.cltv_expiry_delta).ok_or(())?;
+	}
 
-		let mut htlc_min_candidate = tlvs.payment_constraints.htlc_minimum_msat as u128;
-		for (_, node) in intermediate_nodes.iter().skip(idx + 1) {
-			// The min htlc for a hop is that hop's htlc_minimum_msat minus the following hops' fees
-			// because the sender will automatically include that following fee in the amount that this
-			// hop forwards.
-			let prop_fee = node.payment_relay.fee_proportional_millionths as u128;
-			let base_fee = node.payment_relay.fee_base_msat as u128;
-			let hop_fee = htlc_min_candidate
-				.checked_mul(prop_fee)
-				.and_then(|prop_fee| (prop_fee / 1_000_000).checked_add(base_fee))
-				.ok_or(())?;
-			htlc_min_candidate = htlc_min_candidate.saturating_sub(hop_fee);
-			if htlc_min_candidate == 0 { break }
-		}
-		htlc_minimum_msat = core::cmp::max(htlc_min_candidate, htlc_minimum_msat);
+	let mut htlc_minimum_msat = intermediate_nodes.first()
+		.map_or(0, |(_, tlvs)| tlvs.payment_constraints.htlc_minimum_msat) as u128;
+	for (_, tlvs) in intermediate_nodes.iter().skip(1) {
+		let prop_fee = tlvs.payment_relay.fee_proportional_millionths as u128;
+		let base_fee = tlvs.payment_relay.fee_base_msat as u128;
+		let hop_fee = htlc_minimum_msat
+			.checked_mul(prop_fee)
+			.and_then(|prop_fee| (prop_fee / 1_000_000).checked_add(base_fee))
+			.ok_or(())?;
+		htlc_minimum_msat = core::cmp::max(
+			htlc_minimum_msat.saturating_sub(hop_fee), tlvs.payment_constraints.htlc_minimum_msat as u128
+		);
 	}
+	htlc_minimum_msat = core::cmp::max(
+		payee_tlvs.payment_constraints.htlc_minimum_msat as u128, htlc_minimum_msat
+	);
 
 	Ok(BlindedPayInfo {
 		fee_base_msat: u32::try_from(curr_base_fee).map_err(|_| ())?,