diff options
| -rw-r--r-- | src/wallet/coinselection.cpp | 59 | ||||
| -rw-r--r-- | src/wallet/coinselection.h | 46 | ||||
| -rw-r--r-- | src/wallet/spend.cpp | 117 | ||||
| -rw-r--r-- | src/wallet/test/coinselector_tests.cpp | 13 | ||||
| -rw-r--r-- | src/wallet/test/fuzz/coinselection.cpp | 8 |
5 files changed, 153 insertions, 90 deletions
diff --git a/src/wallet/coinselection.cpp b/src/wallet/coinselection.cpp index 49e6bac462..b568e90998 100644 --- a/src/wallet/coinselection.cpp +++ b/src/wallet/coinselection.cpp @@ -156,7 +156,7 @@ std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_poo for (const size_t& i : best_selection) { result.AddInput(utxo_pool.at(i)); } - result.ComputeAndSetWaste(CAmount{0}); + result.ComputeAndSetWaste(cost_of_change, cost_of_change, CAmount{0}); assert(best_waste == result.GetWaste()); return result; @@ -166,6 +166,12 @@ std::optional<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& ut { SelectionResult result(target_value, SelectionAlgorithm::SRD); + // Include change for SRD as we want to avoid making really small change if the selection just + // barely meets the target. Just use the lower bound change target instead of the randomly + // generated one, since SRD will result in a random change amount anyway; avoid making the + // target needlessly large. + target_value += CHANGE_LOWER; + std::vector<size_t> indexes; indexes.resize(utxo_pool.size()); std::iota(indexes.begin(), indexes.end(), 0); @@ -389,20 +395,26 @@ CAmount GetSelectionWaste(const std::set<COutput>& inputs, CAmount change_cost, return waste; } -CAmount GenerateChangeTarget(CAmount payment_value, FastRandomContext& rng) +CAmount GenerateChangeTarget(const CAmount payment_value, const CAmount change_fee, FastRandomContext& rng) { if (payment_value <= CHANGE_LOWER / 2) { - return CHANGE_LOWER; + return change_fee + CHANGE_LOWER; } else { // random value between 50ksat and min (payment_value * 2, 1milsat) const auto upper_bound = std::min(payment_value * 2, CHANGE_UPPER); - return rng.randrange(upper_bound - CHANGE_LOWER) + CHANGE_LOWER; + return change_fee + rng.randrange(upper_bound - CHANGE_LOWER) + CHANGE_LOWER; } } -void SelectionResult::ComputeAndSetWaste(CAmount change_cost) +void SelectionResult::ComputeAndSetWaste(const CAmount min_viable_change, const CAmount change_cost, const CAmount change_fee) { - m_waste = GetSelectionWaste(m_selected_inputs, change_cost, m_target, m_use_effective); + const CAmount change = GetChange(min_viable_change, change_fee); + + if (change > 0) { + m_waste = GetSelectionWaste(m_selected_inputs, change_cost, m_target, m_use_effective); + } else { + m_waste = GetSelectionWaste(m_selected_inputs, 0, m_target, m_use_effective); + } } CAmount SelectionResult::GetWaste() const @@ -415,6 +427,11 @@ CAmount SelectionResult::GetSelectedValue() const return std::accumulate(m_selected_inputs.cbegin(), m_selected_inputs.cend(), CAmount{0}, [](CAmount sum, const auto& coin) { return sum + coin.txout.nValue; }); } +CAmount SelectionResult::GetSelectedEffectiveValue() const +{ + return std::accumulate(m_selected_inputs.cbegin(), m_selected_inputs.cend(), CAmount{0}, [](CAmount sum, const auto& coin) { return sum + coin.GetEffectiveValue(); }); +} + void SelectionResult::Clear() { m_selected_inputs.clear(); @@ -427,6 +444,16 @@ void SelectionResult::AddInput(const OutputGroup& group) m_use_effective = !group.m_subtract_fee_outputs; } +void SelectionResult::Merge(const SelectionResult& other) +{ + m_target += other.m_target; + m_use_effective |= other.m_use_effective; + if (m_algo == SelectionAlgorithm::MANUAL) { + m_algo = other.m_algo; + } + util::insert(m_selected_inputs, other.m_selected_inputs); +} + const std::set<COutput>& SelectionResult::GetInputSet() const { return m_selected_inputs; @@ -464,4 +491,24 @@ std::string GetAlgorithmName(const SelectionAlgorithm algo) } assert(false); } + +CAmount SelectionResult::GetChange(const CAmount min_viable_change, const CAmount change_fee) const +{ + // change = SUM(inputs) - SUM(outputs) - fees + // 1) With SFFO we don't pay any fees + // 2) Otherwise we pay all the fees: + // - input fees are covered by GetSelectedEffectiveValue() + // - non_input_fee is included in m_target + // - change_fee + const CAmount change = m_use_effective + ? GetSelectedEffectiveValue() - m_target - change_fee + : GetSelectedValue() - m_target; + + if (change < min_viable_change) { + return 0; + } + + return change; +} + } // namespace wallet diff --git a/src/wallet/coinselection.h b/src/wallet/coinselection.h index e257d3f7c7..761c2be0b3 100644 --- a/src/wallet/coinselection.h +++ b/src/wallet/coinselection.h @@ -123,6 +123,10 @@ struct CoinSelectionParams { /** 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{0}; + /** Minimum amount for creating a change output. + * If change budget is smaller than min_change then we forgo creation of change output. + */ + CAmount min_viable_change{0}; /** 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. */ @@ -252,6 +256,7 @@ struct OutputGroup /** Choose a random change target for each transaction to make it harder to fingerprint the Core * wallet based on the change output values of transactions it creates. + * Change target covers at least change fees and adds a random value on top of it. * The random value is between 50ksat and min(2 * payment_value, 1milsat) * When payment_value <= 25ksat, the value is just 50ksat. * @@ -261,8 +266,9 @@ struct OutputGroup * coins selected are just sufficient to cover the payment amount ("unnecessary input" heuristic). * * @param[in] payment_value Average payment value of the transaction output(s). + * @param[in] change_fee Fee for creating a change output. */ -[[nodiscard]] CAmount GenerateChangeTarget(CAmount payment_value, FastRandomContext& rng); +[[nodiscard]] CAmount GenerateChangeTarget(const CAmount payment_value, const CAmount change_fee, FastRandomContext& rng); enum class SelectionAlgorithm : uint8_t { @@ -279,17 +285,16 @@ struct SelectionResult private: /** Set of inputs selected by the algorithm to use in the transaction */ std::set<COutput> m_selected_inputs; + /** The target the algorithm selected for. Equal to the recipient amount plus non-input fees */ + CAmount m_target; + /** The algorithm used to produce this result */ + SelectionAlgorithm m_algo; /** Whether the input values for calculations should be the effective value (true) or normal value (false) */ bool m_use_effective{false}; /** The computed waste */ std::optional<CAmount> m_waste; public: - /** The target the algorithm selected for. Note that this may not be equal to the recipient amount as it can include non-input fees */ - const CAmount m_target; - /** The algorithm used to produce this result */ - const SelectionAlgorithm m_algo; - explicit SelectionResult(const CAmount target, SelectionAlgorithm algo) : m_target(target), m_algo(algo) {} @@ -298,20 +303,47 @@ public: /** Get the sum of the input values */ [[nodiscard]] CAmount GetSelectedValue() const; + [[nodiscard]] CAmount GetSelectedEffectiveValue() const; + void Clear(); void AddInput(const OutputGroup& group); /** Calculates and stores the waste for this selection via GetSelectionWaste */ - void ComputeAndSetWaste(CAmount change_cost); + void ComputeAndSetWaste(const CAmount min_viable_change, const CAmount change_cost, const CAmount change_fee); [[nodiscard]] CAmount GetWaste() const; + void Merge(const SelectionResult& other); + /** Get m_selected_inputs */ const std::set<COutput>& GetInputSet() const; /** Get the vector of COutputs that will be used to fill in a CTransaction's vin */ std::vector<COutput> GetShuffledInputVector() const; bool operator<(SelectionResult other) const; + + /** Get the amount for the change output after paying needed fees. + * + * The change amount is not 100% precise due to discrepancies in fee calculation. + * The final change amount (if any) should be corrected after calculating the final tx fees. + * When there is a discrepancy, most of the time the final change would be slightly bigger than estimated. + * + * Following are the possible factors of discrepancy: + * + non-input fees always include segwit flags + * + input fee estimation always include segwit stack size + * + input fees are rounded individually and not collectively, which leads to small rounding errors + * - input counter size is always assumed to be 1vbyte + * + * @param[in] min_viable_change Minimum amount for change output, if change would be less then we forgo change + * @param[in] change_fee Fees to include change output in the tx + * @returns Amount for change output, 0 when there is no change. + * + */ + CAmount GetChange(const CAmount min_viable_change, const CAmount change_fee) const; + + CAmount GetTarget() const { return m_target; } + + SelectionAlgorithm GetAlgo() const { return m_algo; } }; std::optional<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change); diff --git a/src/wallet/spend.cpp b/src/wallet/spend.cpp index 001acd04e2..92cf771358 100644 --- a/src/wallet/spend.cpp +++ b/src/wallet/spend.cpp @@ -502,32 +502,20 @@ std::optional<SelectionResult> ChooseSelectionResult(const CWallet& wallet, cons // Vector of results. We will choose the best one based on waste. std::vector<SelectionResult> results; - // Note that unlike KnapsackSolver, we do not include the fee for creating a change output as BnB will not create a change output. - std::vector<OutputGroup> positive_groups = GroupOutputs(wallet, available_coins, coin_selection_params, eligibility_filter, true /* positive_only */); + std::vector<OutputGroup> positive_groups = GroupOutputs(wallet, available_coins, coin_selection_params, eligibility_filter, /*positive_only=*/true); if (auto bnb_result{SelectCoinsBnB(positive_groups, nTargetValue, coin_selection_params.m_cost_of_change)}) { results.push_back(*bnb_result); } // The knapsack solver has some legacy behavior where it will spend dust outputs. We retain this behavior, so don't filter for positive only here. - std::vector<OutputGroup> all_groups = GroupOutputs(wallet, available_coins, coin_selection_params, eligibility_filter, false /* positive_only */); - CAmount target_with_change = nTargetValue; - // While nTargetValue includes the transaction fees for non-input things, it does not include the fee for creating a change output. - // So we need to include that for KnapsackSolver and SRD as well, as we are expecting to create a change output. - if (!coin_selection_params.m_subtract_fee_outputs) { - target_with_change += coin_selection_params.m_change_fee; - } - if (auto knapsack_result{KnapsackSolver(all_groups, target_with_change, coin_selection_params.m_min_change_target, coin_selection_params.rng_fast)}) { - knapsack_result->ComputeAndSetWaste(coin_selection_params.m_cost_of_change); + std::vector<OutputGroup> all_groups = GroupOutputs(wallet, available_coins, coin_selection_params, eligibility_filter, /*positive_only=*/false); + if (auto knapsack_result{KnapsackSolver(all_groups, nTargetValue, coin_selection_params.m_min_change_target, coin_selection_params.rng_fast)}) { + knapsack_result->ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee); results.push_back(*knapsack_result); } - // Include change for SRD as we want to avoid making really small change if the selection just - // barely meets the target. Just use the lower bound change target instead of the randomly - // generated one, since SRD will result in a random change amount anyway; avoid making the - // target needlessly large. - const CAmount srd_target = target_with_change + CHANGE_LOWER; - if (auto srd_result{SelectCoinsSRD(positive_groups, srd_target, coin_selection_params.rng_fast)}) { - srd_result->ComputeAndSetWaste(coin_selection_params.m_cost_of_change); + if (auto srd_result{SelectCoinsSRD(positive_groups, nTargetValue, coin_selection_params.rng_fast)}) { + srd_result->ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee); results.push_back(*srd_result); } @@ -603,7 +591,7 @@ std::optional<SelectionResult> SelectCoins(const CWallet& wallet, CoinsResult& a SelectionResult result(nTargetValue, SelectionAlgorithm::MANUAL); result.AddInput(preset_inputs); if (result.GetSelectedValue() < nTargetValue) return std::nullopt; - result.ComputeAndSetWaste(coin_selection_params.m_cost_of_change); + result.ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee); return result; } @@ -628,12 +616,15 @@ std::optional<SelectionResult> SelectCoins(const CWallet& wallet, CoinsResult& a available_coins.Shuffle(coin_selection_params.rng_fast); } + SelectionResult preselected(preset_inputs.GetSelectionAmount(), SelectionAlgorithm::MANUAL); + preselected.AddInput(preset_inputs); + // Coin Selection attempts to select inputs from a pool of eligible UTXOs to fund the // transaction at a target feerate. If an attempt fails, more attempts may be made using a more // permissive CoinEligibilityFilter. std::optional<SelectionResult> res = [&] { // Pre-selected inputs already cover the target amount. - if (value_to_select <= 0) return std::make_optional(SelectionResult(nTargetValue, SelectionAlgorithm::MANUAL)); + if (value_to_select <= 0) return std::make_optional(SelectionResult(value_to_select, SelectionAlgorithm::MANUAL)); // If possible, fund the transaction with confirmed UTXOs only. Prefer at least six // confirmations on outputs received from other wallets and only spend confirmed change. @@ -687,9 +678,9 @@ std::optional<SelectionResult> SelectCoins(const CWallet& wallet, CoinsResult& a if (!res) return std::nullopt; // Add preset inputs to result - res->AddInput(preset_inputs); - if (res->m_algo == SelectionAlgorithm::MANUAL) { - res->ComputeAndSetWaste(coin_selection_params.m_cost_of_change); + res->Merge(preselected); + if (res->GetAlgo() == SelectionAlgorithm::MANUAL) { + res->ComputeAndSetWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee); } return res; @@ -803,7 +794,6 @@ static util::Result<CreatedTransactionResult> CreateTransactionInternal( coin_selection_params.m_subtract_fee_outputs = true; } } - coin_selection_params.m_min_change_target = GenerateChangeTarget(std::floor(recipients_sum / vecSend.size()), rng_fast); // Create change script that will be used if we need change CScript scriptChange; @@ -872,6 +862,15 @@ static util::Result<CreatedTransactionResult> CreateTransactionInternal( coin_selection_params.m_change_fee = coin_selection_params.m_effective_feerate.GetFee(coin_selection_params.change_output_size); coin_selection_params.m_cost_of_change = coin_selection_params.m_discard_feerate.GetFee(coin_selection_params.change_spend_size) + coin_selection_params.m_change_fee; + coin_selection_params.m_min_change_target = GenerateChangeTarget(std::floor(recipients_sum / vecSend.size()), coin_selection_params.m_change_fee, rng_fast); + + // The smallest change amount should be: + // 1. at least equal to dust threshold + // 2. at least 1 sat greater than fees to spend it at m_discard_feerate + const auto dust = GetDustThreshold(change_prototype_txout, coin_selection_params.m_discard_feerate); + const auto change_spend_fee = coin_selection_params.m_discard_feerate.GetFee(coin_selection_params.change_spend_size); + coin_selection_params.min_viable_change = std::max(change_spend_fee + 1, dust); + // vouts to the payees if (!coin_selection_params.m_subtract_fee_outputs) { coin_selection_params.tx_noinputs_size = 10; // Static vsize overhead + outputs vsize. 4 nVersion, 4 nLocktime, 1 input count, 1 witness overhead (dummy, flag, stack size) @@ -910,25 +909,22 @@ static util::Result<CreatedTransactionResult> CreateTransactionInternal( if (!result) { return util::Error{_("Insufficient funds")}; } - TRACE5(coin_selection, selected_coins, wallet.GetName().c_str(), GetAlgorithmName(result->m_algo).c_str(), result->m_target, result->GetWaste(), result->GetSelectedValue()); - - // Always make a change output - // We will reduce the fee from this change output later, and remove the output if it is too small. - const CAmount change_and_fee = result->GetSelectedValue() - recipients_sum; - assert(change_and_fee >= 0); - CTxOut newTxOut(change_and_fee, scriptChange); - - if (nChangePosInOut == -1) { - // Insert change txn at random position: - nChangePosInOut = rng_fast.randrange(txNew.vout.size() + 1); - } - else if ((unsigned int)nChangePosInOut > txNew.vout.size()) { - return util::Error{_("Transaction change output index out of range")}; + TRACE5(coin_selection, selected_coins, wallet.GetName().c_str(), GetAlgorithmName(result->GetAlgo()).c_str(), result->GetTarget(), result->GetWaste(), result->GetSelectedValue()); + + const CAmount change_amount = result->GetChange(coin_selection_params.min_viable_change, coin_selection_params.m_change_fee); + if (change_amount > 0) { + CTxOut newTxOut(change_amount, scriptChange); + if (nChangePosInOut == -1) { + // Insert change txn at random position: + nChangePosInOut = rng_fast.randrange(txNew.vout.size() + 1); + } else if ((unsigned int)nChangePosInOut > txNew.vout.size()) { + return util::Error{_("Transaction change output index out of range")}; + } + txNew.vout.insert(txNew.vout.begin() + nChangePosInOut, newTxOut); + } else { + nChangePosInOut = -1; } - assert(nChangePosInOut != -1); - auto change_position = txNew.vout.insert(txNew.vout.begin() + nChangePosInOut, newTxOut); - // Shuffle selected coins and fill in final vin std::vector<COutput> selected_coins = result->GetShuffledInputVector(); @@ -952,42 +948,23 @@ static util::Result<CreatedTransactionResult> CreateTransactionInternal( if (nBytes == -1) { return util::Error{_("Missing solving data for estimating transaction size")}; } - nFeeRet = coin_selection_params.m_effective_feerate.GetFee(nBytes); - - // Subtract fee from the change output if not subtracting it from recipient outputs - CAmount fee_needed = nFeeRet; - if (!coin_selection_params.m_subtract_fee_outputs) { - change_position->nValue -= fee_needed; - } - - // We want to drop the change to fees if: - // 1. The change output would be dust - // 2. The change is within the (almost) exact match window, i.e. it is less than or equal to the cost of the change output (cost_of_change) - CAmount change_amount = change_position->nValue; - if (IsDust(*change_position, coin_selection_params.m_discard_feerate) || change_amount <= coin_selection_params.m_cost_of_change) - { - nChangePosInOut = -1; - change_amount = 0; - txNew.vout.erase(change_position); - - // Because we have dropped this change, the tx size and required fee will be different, so let's recalculate those - tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), &wallet, &coin_control); - nBytes = tx_sizes.vsize; - fee_needed = coin_selection_params.m_effective_feerate.GetFee(nBytes); - } + CAmount fee_needed = coin_selection_params.m_effective_feerate.GetFee(nBytes); + nFeeRet = result->GetSelectedValue() - recipients_sum - change_amount; - // The only time that fee_needed should be less than the amount available for fees (in change_and_fee - change_amount) is when + // The only time that fee_needed should be less than the amount available for fees is when // we are subtracting the fee from the outputs. If this occurs at any other time, it is a bug. - assert(coin_selection_params.m_subtract_fee_outputs || fee_needed <= change_and_fee - change_amount); + assert(coin_selection_params.m_subtract_fee_outputs || fee_needed <= nFeeRet); - // Update nFeeRet in case fee_needed changed due to dropping the change output - if (fee_needed <= change_and_fee - change_amount) { - nFeeRet = change_and_fee - change_amount; + // If there is a change output and we overpay the fees then increase the change to match the fee needed + if (nChangePosInOut != -1 && fee_needed < nFeeRet) { + auto& change = txNew.vout.at(nChangePosInOut); + change.nValue += nFeeRet - fee_needed; + nFeeRet = fee_needed; } // Reduce output values for subtractFeeFromAmount if (coin_selection_params.m_subtract_fee_outputs) { - CAmount to_reduce = fee_needed + change_amount - change_and_fee; + CAmount to_reduce = fee_needed - nFeeRet; int i = 0; bool fFirst = true; for (const auto& recipient : vecSend) diff --git a/src/wallet/test/coinselector_tests.cpp b/src/wallet/test/coinselector_tests.cpp index 4dfdc87a38..30a7fb9eb6 100644 --- a/src/wallet/test/coinselector_tests.cpp +++ b/src/wallet/test/coinselector_tests.cpp @@ -248,9 +248,9 @@ BOOST_AUTO_TEST_CASE(bnb_search_test) // Iteration exhaustion test CAmount target = make_hard_case(17, utxo_pool); - BOOST_CHECK(!SelectCoinsBnB(GroupCoins(utxo_pool), target, 0)); // Should exhaust + BOOST_CHECK(!SelectCoinsBnB(GroupCoins(utxo_pool), target, 1)); // Should exhaust target = make_hard_case(14, utxo_pool); - const auto result7 = SelectCoinsBnB(GroupCoins(utxo_pool), target, 0); // Should not exhaust + const auto result7 = SelectCoinsBnB(GroupCoins(utxo_pool), target, 1); // Should not exhaust BOOST_CHECK(result7); // Test same value early bailout optimization @@ -289,8 +289,8 @@ BOOST_AUTO_TEST_CASE(bnb_search_test) // Make sure that effective value is working in AttemptSelection when BnB is used CoinSelectionParams coin_selection_params_bnb{ rand, - /*change_output_size=*/ 0, - /*change_spend_size=*/ 0, + /*change_output_size=*/ 31, + /*change_spend_size=*/ 68, /*min_change_target=*/ 0, /*effective_feerate=*/ CFeeRate(3000), /*long_term_feerate=*/ CFeeRate(1000), @@ -298,6 +298,9 @@ BOOST_AUTO_TEST_CASE(bnb_search_test) /*tx_noinputs_size=*/ 0, /*avoid_partial=*/ false, }; + coin_selection_params_bnb.m_change_fee = coin_selection_params_bnb.m_effective_feerate.GetFee(coin_selection_params_bnb.change_output_size); + coin_selection_params_bnb.m_cost_of_change = coin_selection_params_bnb.m_effective_feerate.GetFee(coin_selection_params_bnb.change_spend_size) + coin_selection_params_bnb.m_change_fee; + coin_selection_params_bnb.min_viable_change = coin_selection_params_bnb.m_effective_feerate.GetFee(coin_selection_params_bnb.change_spend_size); { std::unique_ptr<CWallet> wallet = std::make_unique<CWallet>(m_node.chain.get(), "", m_args, CreateMockWalletDatabase()); wallet->LoadWallet(); @@ -777,6 +780,8 @@ BOOST_AUTO_TEST_CASE(SelectCoins_test) /*tx_noinputs_size=*/ 0, /*avoid_partial=*/ false, }; + cs_params.m_cost_of_change = 1; + cs_params.min_viable_change = 1; CCoinControl cc; const auto result = SelectCoins(*wallet, available_coins, target, cc, cs_params); BOOST_CHECK(result); diff --git a/src/wallet/test/fuzz/coinselection.cpp b/src/wallet/test/fuzz/coinselection.cpp index 3465f2f331..90a328179e 100644 --- a/src/wallet/test/fuzz/coinselection.cpp +++ b/src/wallet/test/fuzz/coinselection.cpp @@ -58,6 +58,8 @@ FUZZ_TARGET(coinselection) coin_params.m_subtract_fee_outputs = subtract_fee_outputs; coin_params.m_long_term_feerate = long_term_fee_rate; coin_params.m_effective_feerate = effective_fee_rate; + coin_params.change_output_size = fuzzed_data_provider.ConsumeIntegralInRange<int>(10, 1000); + coin_params.m_change_fee = effective_fee_rate.GetFee(coin_params.change_output_size); // Create some coins CAmount total_balance{0}; @@ -83,11 +85,11 @@ FUZZ_TARGET(coinselection) const auto result_bnb = SelectCoinsBnB(group_pos, target, cost_of_change); auto result_srd = SelectCoinsSRD(group_pos, target, fast_random_context); - if (result_srd) result_srd->ComputeAndSetWaste(cost_of_change); + if (result_srd) result_srd->ComputeAndSetWaste(cost_of_change, cost_of_change, 0); - CAmount change_target{GenerateChangeTarget(target, fast_random_context)}; + CAmount change_target{GenerateChangeTarget(target, coin_params.m_change_fee, fast_random_context)}; auto result_knapsack = KnapsackSolver(group_all, target, change_target, fast_random_context); - if (result_knapsack) result_knapsack->ComputeAndSetWaste(cost_of_change); + if (result_knapsack) result_knapsack->ComputeAndSetWaste(cost_of_change, cost_of_change, 0); // If the total balance is sufficient for the target and we are not using // effective values, Knapsack should always find a solution. |