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[refactor]: update coin selection algorithms input parameter `max_wei…
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…ght` name

- This commit renames the coin selection algorithms input parameter `max_weight`
  to `max_selection_weight` for clarity.

  The parameter represent the maximum weight of the UTXOs the coin selection algorithm
  should select, not the transaction maximum weight.

- The commit updates the parameter docstring to provide correct description.

- Also updates coin selection unit and fuzzing test variables to match the new name.
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@ismaelsadeeq
ismaelsadeeq committed Jun 27, 2024
1 parent b27afb7 commit 7f61d31
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Showing 5 changed files with 55 additions and 55 deletions.
26 changes: 13 additions & 13 deletions src/wallet/coinselection.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -84,14 +84,14 @@ struct {
* bound of the range.
* @param const CAmount& cost_of_change This is the cost of creating and spending a change output.
* This plus selection_target is the upper bound of the range.
* @param int max_weight The maximum weight available for the input set.
* @param int max_selection_weight The maximum allowed weight for a selection result to be valid.
* @returns The result of this coin selection algorithm, or std::nullopt
*/

static const size_t TOTAL_TRIES = 100000;

util::Result<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change,
int max_weight)
int max_selection_weight)
{
SelectionResult result(selection_target, SelectionAlgorithm::BNB);
CAmount curr_value = 0;
Expand Down Expand Up @@ -128,7 +128,7 @@ util::Result<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool
curr_value > selection_target + cost_of_change || // Selected value is out of range, go back and try other branch
(curr_waste > best_waste && is_feerate_high)) { // Don't select things which we know will be more wasteful if the waste is increasing
backtrack = true;
} else if (curr_selection_weight > max_weight) { // Exceeding weight for standard tx, cannot find more solutions by adding more inputs
} else if (curr_selection_weight > max_selection_weight) { // Selected UTXOs weight exceeds the maximum weight allowed, cannot find more solutions by adding more inputs
max_tx_weight_exceeded = true; // at least one selection attempt exceeded the max weight
backtrack = true;
} else if (curr_value >= selection_target) { // Selected value is within range
Expand Down Expand Up @@ -319,10 +319,10 @@ util::Result<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool
* group with multiple as a heavier UTXO with the combined amount here.)
* @param const CAmount& selection_target This is the minimum amount that we need for the transaction without considering change.
* @param const CAmount& change_target The minimum budget for creating a change output, by which we increase the selection_target.
* @param int max_weight The maximum permitted weight for the input set.
* @param int max_selection_weight The maximum allowed weight for a selection result to be valid.
* @returns The result of this coin selection algorithm, or std::nullopt
*/
util::Result<SelectionResult> CoinGrinder(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, CAmount change_target, int max_weight)
util::Result<SelectionResult> CoinGrinder(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, CAmount change_target, int max_selection_weight)
{
std::sort(utxo_pool.begin(), utxo_pool.end(), descending_effval_weight);
// The sum of UTXO amounts after this UTXO index, e.g. lookahead[5] = Σ(UTXO[6+].amount)
Expand Down Expand Up @@ -359,7 +359,7 @@ util::Result<SelectionResult> CoinGrinder(std::vector<OutputGroup>& utxo_pool, c

// The weight of the currently selected input set, and the weight of the best selection
int curr_weight = 0;
int best_selection_weight = max_weight; // Tie is fine, because we prefer lower selection amount
int best_selection_weight = max_selection_weight; // Tie is fine, because we prefer lower selection amount

// Whether the input sets generated during this search have exceeded the maximum transaction weight at any point
bool max_tx_weight_exceeded = false;
Expand Down Expand Up @@ -436,8 +436,8 @@ util::Result<SelectionResult> CoinGrinder(std::vector<OutputGroup>& utxo_pool, c
// Insufficient funds with lookahead: CUT
should_cut = true;
} else if (curr_weight > best_selection_weight) {
// best_selection_weight is initialized to max_weight
if (curr_weight > max_weight) max_tx_weight_exceeded = true;
// best_selection_weight is initialized to max_selection_weight
if (curr_weight > max_selection_weight) max_tx_weight_exceeded = true;
// Worse weight than best solution. More UTXOs only increase weight:
// CUT if last selected group had minimal weight, else SHIFT
if (utxo_pool[curr_tail].m_weight <= min_tail_weight[curr_tail]) {
Expand Down Expand Up @@ -535,7 +535,7 @@ class MinOutputGroupComparator
};

util::Result<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value, CAmount change_fee, FastRandomContext& rng,
int max_weight)
int max_selection_weight)
{
SelectionResult result(target_value, SelectionAlgorithm::SRD);
std::priority_queue<OutputGroup, std::vector<OutputGroup>, MinOutputGroupComparator> heap;
Expand Down Expand Up @@ -565,14 +565,14 @@ util::Result<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utx

// If the selection weight exceeds the maximum allowed size, remove the least valuable inputs until we
// are below max weight.
if (weight > max_weight) {
if (weight > max_selection_weight) {
max_tx_weight_exceeded = true; // mark it in case we don't find any useful result.
do {
const OutputGroup& to_remove_group = heap.top();
selected_eff_value -= to_remove_group.GetSelectionAmount();
weight -= to_remove_group.m_weight;
heap.pop();
} while (!heap.empty() && weight > max_weight);
} while (!heap.empty() && weight > max_selection_weight);
}

// Now check if we are above the target
Expand Down Expand Up @@ -648,7 +648,7 @@ static void ApproximateBestSubset(FastRandomContext& insecure_rand, const std::v
}

util::Result<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue,
CAmount change_target, FastRandomContext& rng, int max_weight)
CAmount change_target, FastRandomContext& rng, int max_selection_weight)
{
SelectionResult result(nTargetValue, SelectionAlgorithm::KNAPSACK);

Expand Down Expand Up @@ -709,7 +709,7 @@ util::Result<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, c
}

// If the result exceeds the maximum allowed size, return closest UTXO above the target
if (result.GetWeight() > max_weight) {
if (result.GetWeight() > max_selection_weight) {
// No coin above target, nothing to do.
if (!lowest_larger) return ErrorMaxWeightExceeded();

Expand Down
10 changes: 5 additions & 5 deletions src/wallet/coinselection.h
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Original file line number Diff line number Diff line change
Expand Up @@ -440,25 +440,25 @@ struct SelectionResult
};

util::Result<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change,
int max_weight);
int max_selection_weight);

util::Result<SelectionResult> CoinGrinder(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, CAmount change_target, int max_weight);
util::Result<SelectionResult> CoinGrinder(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, CAmount change_target, int max_selection_weight);

/** Select coins by Single Random Draw. OutputGroups are selected randomly from the eligible
* outputs until the target is satisfied
*
* @param[in] utxo_pool The positive effective value OutputGroups eligible for selection
* @param[in] target_value The target value to select for
* @param[in] rng The randomness source to shuffle coins
* @param[in] max_weight The maximum allowed weight for a selection result to be valid
* @param[in] max_selection_weight The maximum allowed weight for a selection result to be valid
* @returns If successful, a valid SelectionResult, otherwise, util::Error
*/
util::Result<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value, CAmount change_fee, FastRandomContext& rng,
int max_weight);
int max_selection_weight);

// Original coin selection algorithm as a fallback
util::Result<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue,
CAmount change_target, FastRandomContext& rng, int max_weight);
CAmount change_target, FastRandomContext& rng, int max_selection_weight);
} // namespace wallet

#endif // BITCOIN_WALLET_COINSELECTION_H
14 changes: 7 additions & 7 deletions src/wallet/spend.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -695,34 +695,34 @@ util::Result<SelectionResult> ChooseSelectionResult(interfaces::Chain& chain, co
}
};

// Maximum allowed weight
int max_inputs_weight = MAX_STANDARD_TX_WEIGHT - (coin_selection_params.tx_noinputs_size * WITNESS_SCALE_FACTOR);
// Maximum allowed weight for selected coins.
int max_selection_weight = MAX_STANDARD_TX_WEIGHT - (coin_selection_params.tx_noinputs_size * WITNESS_SCALE_FACTOR);

// SFFO frequently causes issues in the context of changeless input sets: skip BnB when SFFO is active
if (!coin_selection_params.m_subtract_fee_outputs) {
if (auto bnb_result{SelectCoinsBnB(groups.positive_group, nTargetValue, coin_selection_params.m_cost_of_change, max_inputs_weight)}) {
if (auto bnb_result{SelectCoinsBnB(groups.positive_group, nTargetValue, coin_selection_params.m_cost_of_change, max_selection_weight)}) {
results.push_back(*bnb_result);
} else append_error(std::move(bnb_result));
}

// As Knapsack and SRD can create change, also deduce change weight.
max_inputs_weight -= (coin_selection_params.change_output_size * WITNESS_SCALE_FACTOR);
max_selection_weight -= (coin_selection_params.change_output_size * WITNESS_SCALE_FACTOR);

// 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.
if (auto knapsack_result{KnapsackSolver(groups.mixed_group, nTargetValue, coin_selection_params.m_min_change_target, coin_selection_params.rng_fast, max_inputs_weight)}) {
if (auto knapsack_result{KnapsackSolver(groups.mixed_group, nTargetValue, coin_selection_params.m_min_change_target, coin_selection_params.rng_fast, max_selection_weight)}) {
results.push_back(*knapsack_result);
} else append_error(std::move(knapsack_result));

if (coin_selection_params.m_effective_feerate > CFeeRate{3 * coin_selection_params.m_long_term_feerate}) { // Minimize input set for feerates of at least 3×LTFRE (default: 30 ṩ/vB+)
if (auto cg_result{CoinGrinder(groups.positive_group, nTargetValue, coin_selection_params.m_min_change_target, max_inputs_weight)}) {
if (auto cg_result{CoinGrinder(groups.positive_group, nTargetValue, coin_selection_params.m_min_change_target, max_selection_weight)}) {
cg_result->RecalculateWaste(coin_selection_params.min_viable_change, coin_selection_params.m_cost_of_change, coin_selection_params.m_change_fee);
results.push_back(*cg_result);
} else {
append_error(std::move(cg_result));
}
}

if (auto srd_result{SelectCoinsSRD(groups.positive_group, nTargetValue, coin_selection_params.m_change_fee, coin_selection_params.rng_fast, max_inputs_weight)}) {
if (auto srd_result{SelectCoinsSRD(groups.positive_group, nTargetValue, coin_selection_params.m_change_fee, coin_selection_params.rng_fast, max_selection_weight)}) {
results.push_back(*srd_result);
} else append_error(std::move(srd_result));

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