refactor coin selection for parameterizable change target

no behavior changes, since the target is always MIN_CHANGE

1 files changed, 8 insertions, 2 deletions

diff --git a/src/wallet/coinselection.h b/src/wallet/coinselection.h
index 504d57aa78..480c9664ca 100644
--- a/src/wallet/coinselection.h
+++ b/src/wallet/coinselection.h
@@ -94,6 +94,9 @@ struct CoinSelectionParams {
     size_t change_output_size = 0;
     /** Size of the input to spend a change output in virtual bytes. */
     size_t change_spend_size = 0;
+    /** Mininmum change to target in Knapsack solver: select coins to cover the payment and
+     * at least this value of change. */
+    CAmount m_min_change_target{MIN_CHANGE};
     /** Cost of creating the change output. */
     CAmount m_change_fee{0};
     /** Cost of creating the change output + cost of spending the change output in the future. */
@@ -115,11 +118,13 @@ struct CoinSelectionParams {
      * reuse. Dust outputs are not eligible to be added to output groups and thus not considered. */
     bool m_avoid_partial_spends = false;
 
-    CoinSelectionParams(FastRandomContext& rng_fast, size_t change_output_size, size_t change_spend_size, CFeeRate effective_feerate,
+    CoinSelectionParams(FastRandomContext& rng_fast, size_t change_output_size, size_t change_spend_size,
+                        CAmount min_change_target, CFeeRate effective_feerate,
                         CFeeRate long_term_feerate, CFeeRate discard_feerate, size_t tx_noinputs_size, bool avoid_partial)
         : rng_fast{rng_fast},
           change_output_size(change_output_size),
           change_spend_size(change_spend_size),
+          m_min_change_target(min_change_target),
           m_effective_feerate(effective_feerate),
           m_long_term_feerate(long_term_feerate),
           m_discard_feerate(discard_feerate),
@@ -267,7 +272,8 @@ std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_poo
 std::optional<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value, FastRandomContext& rng);
 
 // Original coin selection algorithm as a fallback
-std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue, FastRandomContext& rng);
+std::optional<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue,
+                                              CAmount change_target, FastRandomContext& rng);
 } // namespace wallet
 
 #endif // BITCOIN_WALLET_COINSELECTION_H