Add Largest First Selector

src/wallet/coinselection.cpp

@@ -542,6 +542,34 @@ class MinOutputGroupComparator
     }
 };
 
+util::Result<SelectionResult> LargestFirst(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, CAmount change_target, int max_weight)
+{
+    SelectionResult result(selection_target, SelectionAlgorithm::LF);
+
+    // Include a minimum change budget for Largest First as we want to avoid
+    // making really small change if the selection just barely meets the target.
+    const CAmount total_target = selection_target + change_target;
+
+    std::sort(utxo_pool.begin(), utxo_pool.end(), descending);
+    CAmount selected_amount = 0;
+    int weight = 0;
+
+    for (const OutputGroup& group : utxo_pool) {
+        weight += group.m_weight;
+        selected_amount += group.GetSelectionAmount();
+        result.AddInput(group);
+        if (weight > max_weight) {
+            return ErrorMaxWeightExceeded();
+        }
+        if (selected_amount >= total_target) {
+            return result;
+        }
+    }
+
+    // Didn’t find a solution
+    return util::Error();
+}
+
 util::Result<SelectionResult> SandCompactor(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, CAmount change_target, int max_weight)
 {
     SelectionResult result(selection_target, SelectionAlgorithm::SC);

src/wallet/coinselection.h

@@ -313,7 +313,8 @@ enum class SelectionAlgorithm : uint8_t
     SRD = 2,
     CG = 3,
     SC = 4,
-    MANUAL = 5,
+    LF = 5,
+    MANUAL = 6,
 };
 
 std::string GetAlgorithmName(const SelectionAlgorithm algo);
@@ -450,6 +451,17 @@ util::Result<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool
 
 util::Result<SelectionResult> CoinGrinder(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, CAmount change_target, int max_weight);
 
+/**
+ * Largest first selector picks UTXOs from highest effective value to lowest effective value.
+ *
+ * @param[in]  utxo_pool        The OutputGroups eligible for selection
+ * @param[in]  selection_target The target value to select for
+ * @param[in]  change_target    The minimum budget necessary to create a change output
+ * @param[in]  max_weight       The maximum allowed weight for a selection result to be valid
+ * @returns If successful, a valid SelectionResult, otherwise, util::Error
+ */
+util::Result<SelectionResult> LargestFirst(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, CAmount change_target, int max_weight);
+
 
 /**
  * Sand Compactor selects OutputGroups by descending confirmation count (FIFO). If there are multiple UTXOs in an

src/wallet/spend.cpp

@@ -718,6 +718,11 @@ util::Result<SelectionResult> ChooseSelectionResult(interfaces::Chain& chain, co
         }
     }
 
+    // Allow Largest First to spend UTXOs with negative effective value at any feerate
+    if (auto lf_result{LargestFirst(groups.mixed_group, nTargetValue, coin_selection_params.m_min_change_target, max_inputs_weight)}) {
+        results.push_back(*lf_result);
+    } else append_error(lf_result);
+
     // Allow SandCompactor to spend UTXOs with negative effective value at any feerate
     if (auto sc_result{SandCompactor(groups.mixed_group, nTargetValue, coin_selection_params.m_min_change_target, max_inputs_weight)}) {
         results.push_back(*sc_result);