Use SelectCoinsSRD if it has less waste

Try to find a solution with SelectCoinsSRD. If we do have one, add it to
the list of solutions from which we choose the one with the least waste
as the solution to use.

1 files changed, 9 insertions, 0 deletions

diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp
index 4a7a268982..1724375f4c 100644
--- a/src/wallet/spend.cpp
+++ b/src/wallet/spend.cpp
@@ -387,6 +387,15 @@ bool AttemptSelection(const CWallet& wallet, const CAmount& nTargetValue, const
         results.emplace_back(std::make_tuple(waste, std::move(knapsack_coins), knapsack_value));
     }
 
+    // We include the minimum final change for SRD as we do want to avoid making really small change.
+    // KnapsackSolver does not need this because it includes MIN_CHANGE internally.
+    const CAmount srd_target = nTargetValue + coin_selection_params.m_change_fee + MIN_FINAL_CHANGE;
+    auto srd_result = SelectCoinsSRD(positive_groups, srd_target);
+    if (srd_result != std::nullopt) {
+        const auto waste = GetSelectionWaste(srd_result->first, coin_selection_params.m_cost_of_change, srd_target, !coin_selection_params.m_subtract_fee_outputs);
+        results.emplace_back(std::make_tuple(waste, std::move(srd_result->first), srd_result->second));
+    }
+
     if (results.size() == 0) {
         // No solution found
         return false;