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1 : : // Copyright (c) 2017-2022 The Bitcoin Core developers
2 : : // Distributed under the MIT software license, see the accompanying
3 : : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
4 : :
5 : : #include <wallet/coinselection.h>
6 : :
7 : : #include <common/system.h>
8 : : #include <consensus/amount.h>
9 : : #include <consensus/consensus.h>
10 : : #include <interfaces/chain.h>
11 : : #include <logging.h>
12 : : #include <policy/feerate.h>
13 : : #include <util/check.h>
14 : : #include <util/moneystr.h>
15 : :
16 : : #include <numeric>
17 : : #include <optional>
18 : : #include <queue>
19 : :
20 : : namespace wallet {
21 : : // Common selection error across the algorithms
22 : 22 : static util::Result<SelectionResult> ErrorMaxWeightExceeded()
23 : : {
24 : 22 : return util::Error{_("The inputs size exceeds the maximum weight. "
25 : 22 : "Please try sending a smaller amount or manually consolidating your wallet's UTXOs")};
26 : : }
27 : :
28 : : // Sort by descending (effective) value prefer lower waste on tie
29 : : struct {
30 : 4873052 : bool operator()(const OutputGroup& a, const OutputGroup& b) const
31 : : {
32 [ + + ]: 4873052 : if (a.GetSelectionAmount() == b.GetSelectionAmount()) {
33 : : // Lower waste is better when effective_values are tied
34 : 2474063 : return (a.fee - a.long_term_fee) < (b.fee - b.long_term_fee);
35 : : }
36 : 2398989 : return a.GetSelectionAmount() > b.GetSelectionAmount();
37 : : }
38 : : } descending;
39 : :
40 : : // Sort by descending (effective) value prefer lower weight on tie
41 : : struct {
42 : 7475 : bool operator()(const OutputGroup& a, const OutputGroup& b) const
43 : : {
44 [ + + ]: 7475 : if (a.GetSelectionAmount() == b.GetSelectionAmount()) {
45 : : // Sort lower weight to front on tied effective_value
46 : 2395 : return a.m_weight < b.m_weight;
47 : : }
48 : 5080 : return a.GetSelectionAmount() > b.GetSelectionAmount();
49 : : }
50 : : } descending_effval_weight;
51 : :
52 : : /*
53 : : * This is the Branch and Bound Coin Selection algorithm designed by Murch. It searches for an input
54 : : * set that can pay for the spending target and does not exceed the spending target by more than the
55 : : * cost of creating and spending a change output. The algorithm uses a depth-first search on a binary
56 : : * tree. In the binary tree, each node corresponds to the inclusion or the omission of a UTXO. UTXOs
57 : : * are sorted by their effective values and the tree is explored deterministically per the inclusion
58 : : * branch first. At each node, the algorithm checks whether the selection is within the target range.
59 : : * While the selection has not reached the target range, more UTXOs are included. When a selection's
60 : : * value exceeds the target range, the complete subtree deriving from this selection can be omitted.
61 : : * At that point, the last included UTXO is deselected and the corresponding omission branch explored
62 : : * instead. The search ends after the complete tree has been searched or after a limited number of tries.
63 : : *
64 : : * The search continues to search for better solutions after one solution has been found. The best
65 : : * solution is chosen by minimizing the waste metric. The waste metric is defined as the cost to
66 : : * spend the current inputs at the given fee rate minus the long term expected cost to spend the
67 : : * inputs, plus the amount by which the selection exceeds the spending target:
68 : : *
69 : : * waste = selectionTotal - target + inputs × (currentFeeRate - longTermFeeRate)
70 : : *
71 : : * The algorithm uses two additional optimizations. A lookahead keeps track of the total value of
72 : : * the unexplored UTXOs. A subtree is not explored if the lookahead indicates that the target range
73 : : * cannot be reached. Further, it is unnecessary to test equivalent combinations. This allows us
74 : : * to skip testing the inclusion of UTXOs that match the effective value and waste of an omitted
75 : : * predecessor.
76 : : *
77 : : * The Branch and Bound algorithm is described in detail in Murch's Master Thesis:
78 : : * https://murch.one/wp-content/uploads/2016/11/erhardt2016coinselection.pdf
79 : : *
80 : : * @param const std::vector<OutputGroup>& utxo_pool The set of UTXO groups that we are choosing from.
81 : : * These UTXO groups will be sorted in descending order by effective value and the OutputGroups'
82 : : * values are their effective values.
83 : : * @param const CAmount& selection_target This is the value that we want to select. It is the lower
84 : : * bound of the range.
85 : : * @param const CAmount& cost_of_change This is the cost of creating and spending a change output.
86 : : * This plus selection_target is the upper bound of the range.
87 : : * @param int max_selection_weight The maximum allowed weight for a selection result to be valid.
88 : : * @returns The result of this coin selection algorithm, or std::nullopt
89 : : */
90 : :
91 : : static const size_t TOTAL_TRIES = 100000;
92 : :
93 : 229 : util::Result<SelectionResult> SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change,
94 : : int max_selection_weight)
95 : : {
96 : 229 : SelectionResult result(selection_target, SelectionAlgorithm::BNB);
97 : 229 : CAmount curr_value = 0;
98 : 229 : std::vector<size_t> curr_selection; // selected utxo indexes
99 : 229 : int curr_selection_weight = 0; // sum of selected utxo weight
100 : :
101 : : // Calculate curr_available_value
102 : 229 : CAmount curr_available_value = 0;
103 [ + + ]: 164960 : for (const OutputGroup& utxo : utxo_pool) {
104 : : // Assert that this utxo is not negative. It should never be negative,
105 : : // effective value calculation should have removed it
106 [ + - - + ]: 164731 : assert(utxo.GetSelectionAmount() > 0);
107 [ + - ]: 164731 : curr_available_value += utxo.GetSelectionAmount();
108 : : }
109 [ + + ]: 229 : if (curr_available_value < selection_target) {
110 : 6 : return util::Error();
111 : : }
112 : :
113 : : // Sort the utxo_pool
114 [ + - ]: 226 : std::sort(utxo_pool.begin(), utxo_pool.end(), descending);
115 : :
116 : 226 : CAmount curr_waste = 0;
117 : 226 : std::vector<size_t> best_selection;
118 : 226 : CAmount best_waste = MAX_MONEY;
119 : :
120 [ + - + - ]: 226 : bool is_feerate_high = utxo_pool.at(0).fee > utxo_pool.at(0).long_term_fee;
121 : 226 : bool max_tx_weight_exceeded = false;
122 : :
123 : : // Depth First search loop for choosing the UTXOs
124 [ + + ]: 11085494 : for (size_t curr_try = 0, utxo_pool_index = 0; curr_try < TOTAL_TRIES; ++curr_try, ++utxo_pool_index) {
125 : : // Conditions for starting a backtrack
126 : 11085384 : bool backtrack = false;
127 [ + + ]: 11085384 : if (curr_value + curr_available_value < selection_target || // Cannot possibly reach target with the amount remaining in the curr_available_value.
128 [ + + ]: 9682896 : curr_value > selection_target + cost_of_change || // Selected value is out of range, go back and try other branch
129 [ + + ]: 5995052 : (curr_waste > best_waste && is_feerate_high)) { // Don't select things which we know will be more wasteful if the waste is increasing
130 : : backtrack = true;
131 [ + + ]: 5995048 : } else if (curr_selection_weight > max_selection_weight) { // Selected UTXOs weight exceeds the maximum weight allowed, cannot find more solutions by adding more inputs
132 : : max_tx_weight_exceeded = true; // at least one selection attempt exceeded the max weight
133 : : backtrack = true;
134 [ + + ]: 5995010 : } else if (curr_value >= selection_target) { // Selected value is within range
135 : 24649 : curr_waste += (curr_value - selection_target); // This is the excess value which is added to the waste for the below comparison
136 : : // Adding another UTXO after this check could bring the waste down if the long term fee is higher than the current fee.
137 : : // However we are not going to explore that because this optimization for the waste is only done when we have hit our target
138 : : // value. Adding any more UTXOs will be just burning the UTXO; it will go entirely to fees. Thus we aren't going to
139 : : // explore any more UTXOs to avoid burning money like that.
140 [ + + ]: 24649 : if (curr_waste <= best_waste) {
141 [ + - ]: 12402 : best_selection = curr_selection;
142 : : best_waste = curr_waste;
143 : : }
144 : 24649 : curr_waste -= (curr_value - selection_target); // Remove the excess value as we will be selecting different coins now
145 : 24649 : backtrack = true;
146 : : }
147 : :
148 : 24649 : if (backtrack) { // Backtracking, moving backwards
149 [ + + ]: 5115023 : if (curr_selection.empty()) { // We have walked back to the first utxo and no branch is untraversed. All solutions searched
150 : : break;
151 : : }
152 : :
153 : : // Add omitted UTXOs back to lookahead before traversing the omission branch of last included UTXO.
154 [ + + ]: 10926614 : for (--utxo_pool_index; utxo_pool_index > curr_selection.back(); --utxo_pool_index) {
155 [ + - + - ]: 5811707 : curr_available_value += utxo_pool.at(utxo_pool_index).GetSelectionAmount();
156 : : }
157 : :
158 : : // Output was included on previous iterations, try excluding now.
159 [ - + ]: 5114907 : assert(utxo_pool_index == curr_selection.back());
160 [ + - ]: 5114907 : OutputGroup& utxo = utxo_pool.at(utxo_pool_index);
161 [ + - ]: 5114907 : curr_value -= utxo.GetSelectionAmount();
162 : 5114907 : curr_waste -= utxo.fee - utxo.long_term_fee;
163 : 5114907 : curr_selection_weight -= utxo.m_weight;
164 : 5114907 : curr_selection.pop_back();
165 : : } else { // Moving forwards, continuing down this branch
166 [ + - ]: 5970361 : OutputGroup& utxo = utxo_pool.at(utxo_pool_index);
167 : :
168 : : // Remove this utxo from the curr_available_value utxo amount
169 [ + - ]: 5970361 : curr_available_value -= utxo.GetSelectionAmount();
170 : :
171 : 11938942 : if (curr_selection.empty() ||
172 : : // The previous index is included and therefore not relevant for exclusion shortcut
173 [ + + + + ]: 10502205 : (utxo_pool_index - 1) == curr_selection.back() ||
174 : : // Avoid searching a branch if the previous UTXO has the same value and same waste and was excluded.
175 : : // Since the ratio of fee to long term fee is the same, we only need to check if one of those values match in order to know that the waste is the same.
176 [ + + + - : 10503985 : utxo.GetSelectionAmount() != utxo_pool.at(utxo_pool_index - 1).GetSelectionAmount() ||
+ - + - ]
177 [ + - + + ]: 822812 : utxo.fee != utxo_pool.at(utxo_pool_index - 1).fee)
178 : : {
179 : : // Inclusion branch first (Largest First Exploration)
180 [ + - ]: 5147552 : curr_selection.push_back(utxo_pool_index);
181 [ + - ]: 5147552 : curr_value += utxo.GetSelectionAmount();
182 : 5147552 : curr_waste += utxo.fee - utxo.long_term_fee;
183 : 5147552 : curr_selection_weight += utxo.m_weight;
184 : : }
185 : : }
186 : : }
187 : :
188 : : // Check for solution
189 [ + + ]: 226 : if (best_selection.empty()) {
190 [ + + + - ]: 216 : return max_tx_weight_exceeded ? ErrorMaxWeightExceeded() : util::Error();
191 : : }
192 : :
193 : : // Set output set
194 [ + + ]: 27068 : for (const size_t& i : best_selection) {
195 [ + - + - ]: 26954 : result.AddInput(utxo_pool.at(i));
196 : : }
197 [ + - ]: 114 : result.RecalculateWaste(cost_of_change, cost_of_change, CAmount{0});
198 [ + - - + ]: 114 : assert(best_waste == result.GetWaste());
199 : :
200 : 114 : return result;
201 : 455 : }
202 : :
203 : : /*
204 : : * TL;DR: Coin Grinder is a DFS-based algorithm that deterministically searches for the minimum-weight input set to fund
205 : : * the transaction. The algorithm is similar to the Branch and Bound algorithm, but will produce a transaction _with_ a
206 : : * change output instead of a changeless transaction.
207 : : *
208 : : * Full description: CoinGrinder can be thought of as a graph walking algorithm. It explores a binary tree
209 : : * representation of the powerset of the UTXO pool. Each node in the tree represents a candidate input set. The tree’s
210 : : * root is the empty set. Each node in the tree has two children which are formed by either adding or skipping the next
211 : : * UTXO ("inclusion/omission branch"). Each level in the tree after the root corresponds to a decision about one UTXO in
212 : : * the UTXO pool.
213 : : *
214 : : * Example:
215 : : * We represent UTXOs as _alias=[effective_value/weight]_ and indicate omitted UTXOs with an underscore. Given a UTXO
216 : : * pool {A=[10/2], B=[7/1], C=[5/1], D=[4/2]} sorted by descending effective value, our search tree looks as follows:
217 : : *
218 : : * _______________________ {} ________________________
219 : : * / \
220 : : * A=[10/2] __________ {A} _________ __________ {_} _________
221 : : * / \ / \
222 : : * B=[7/1] {AB} _ {A_} _ {_B} _ {__} _
223 : : * / \ / \ / \ / \
224 : : * C=[5/1] {ABC} {AB_} {A_C} {A__} {_BC} {_B_} {__C} {___}
225 : : * / \ / \ / \ / \ / \ / \ / \ / \
226 : : * D=[4/2] {ABCD} {ABC_} {AB_D} {AB__} {A_CD} {A_C_} {A__D} {A___} {_BCD} {_BC_} {_B_D} {_B__} {__CD} {__C_} {___D} {____}
227 : : *
228 : : *
229 : : * CoinGrinder uses a depth-first search to walk this tree. It first tries inclusion branches, then omission branches. A
230 : : * naive exploration of a tree with four UTXOs requires visiting all 31 nodes:
231 : : *
232 : : * {} {A} {AB} {ABC} {ABCD} {ABC_} {AB_} {AB_D} {AB__} {A_} {A_C} {A_CD} {A_C_} {A__} {A__D} {A___} {_} {_B} {_BC}
233 : : * {_BCD} {_BC_} {_B_} {_B_D} {_B__} {__} {__C} {__CD} {__C} {___} {___D} {____}
234 : : *
235 : : * As powersets grow exponentially with the set size, walking the entire tree would quickly get computationally
236 : : * infeasible with growing UTXO pools. Thanks to traversing the tree in a deterministic order, we can keep track of the
237 : : * progress of the search solely on basis of the current selection (and the best selection so far). We visit as few
238 : : * nodes as possible by recognizing and skipping any branches that can only contain solutions worse than the best
239 : : * solution so far. This makes CoinGrinder a branch-and-bound algorithm
240 : : * (https://en.wikipedia.org/wiki/Branch_and_bound).
241 : : * CoinGrinder is searching for the input set with lowest weight that can fund a transaction, so for example we can only
242 : : * ever find a _better_ candidate input set in a node that adds a UTXO, but never in a node that skips a UTXO. After
243 : : * visiting {A} and exploring the inclusion branch {AB} and its descendants, the candidate input set in the omission
244 : : * branch {A_} is equivalent to the parent {A} in effective value and weight. While CoinGrinder does need to visit the
245 : : * descendants of the omission branch {A_}, it is unnecessary to evaluate the candidate input set in the omission branch
246 : : * itself. By skipping evaluation of all nodes on an omission branch we reduce the visited nodes to 15:
247 : : *
248 : : * {A} {AB} {ABC} {ABCD} {AB_D} {A_C} {A_CD} {A__D} {_B} {_BC} {_BCD} {_B_D} {__C} {__CD} {___D}
249 : : *
250 : : * _______________________ {} ________________________
251 : : * / \
252 : : * A=[10/2] __________ {A} _________ ___________\____________
253 : : * / \ / \
254 : : * B=[7/1] {AB} __ __\_____ {_B} __ __\_____
255 : : * / \ / \ / \ / \
256 : : * C=[5/1] {ABC} \ {A_C} \ {_BC} \ {__C} \
257 : : * / / / / / / / /
258 : : * D=[4/2] {ABCD} {AB_D} {A_CD} {A__D} {_BCD} {_B_D} {__CD} {___D}
259 : : *
260 : : *
261 : : * We refer to the move from the inclusion branch {AB} via the omission branch {A_} to its inclusion-branch child {A_C}
262 : : * as _shifting to the omission branch_ or just _SHIFT_. (The index of the ultimate element in the candidate input set
263 : : * shifts right by one: {AB} ⇒ {A_C}.)
264 : : * When we reach a leaf node in the last level of the tree, shifting to the omission branch is not possible. Instead we
265 : : * go to the omission branch of the node’s last ancestor on an inclusion branch: from {ABCD}, we go to {AB_D}. From
266 : : * {AB_D}, we go to {A_C}. We refer to this operation as a _CUT_. (The ultimate element in
267 : : * the input set is deselected, and the penultimate element is shifted right by one: {AB_D} ⇒ {A_C}.)
268 : : * If a candidate input set in a node has not selected sufficient funds to build the transaction, we continue directly
269 : : * along the next inclusion branch. We call this operation _EXPLORE_. (We go from one inclusion branch to the next
270 : : * inclusion branch: {_B} ⇒ {_BC}.)
271 : : * Further, any prefix that already has selected sufficient effective value to fund the transaction cannot be improved
272 : : * by adding more UTXOs. If for example the candidate input set in {AB} is a valid solution, all potential descendant
273 : : * solutions {ABC}, {ABCD}, and {AB_D} must have a higher weight, thus instead of exploring the descendants of {AB}, we
274 : : * can SHIFT from {AB} to {A_C}.
275 : : *
276 : : * Given the above UTXO set, using a target of 11, and following these initial observations, the basic implementation of
277 : : * CoinGrinder visits the following 10 nodes:
278 : : *
279 : : * Node [eff_val/weight] Evaluation
280 : : * ---------------------------------------------------------------
281 : : * {A} [10/2] Insufficient funds: EXPLORE
282 : : * {AB} [17/3] Solution: SHIFT to omission branch
283 : : * {A_C} [15/3] Better solution: SHIFT to omission branch
284 : : * {A__D} [14/4] Worse solution, shift impossible due to leaf node: CUT to omission branch of {A__D},
285 : : * i.e. SHIFT to omission branch of {A}
286 : : * {_B} [7/1] Insufficient funds: EXPLORE
287 : : * {_BC} [12/2] Better solution: SHIFT to omission branch
288 : : * {_B_D} [11/3] Worse solution, shift impossible due to leaf node: CUT to omission branch of {_B_D},
289 : : * i.e. SHIFT to omission branch of {_B}
290 : : * {__C} [5/1] Insufficient funds: EXPLORE
291 : : * {__CD} [9/3] Insufficient funds, leaf node: CUT
292 : : * {___D} [4/2] Insufficient funds, leaf node, cannot CUT since only one UTXO selected: done.
293 : : *
294 : : * _______________________ {} ________________________
295 : : * / \
296 : : * A=[10/2] __________ {A} _________ ___________\____________
297 : : * / \ / \
298 : : * B=[7/1] {AB} __\_____ {_B} __ __\_____
299 : : * / \ / \ / \
300 : : * C=[5/1] {A_C} \ {_BC} \ {__C} \
301 : : * / / / /
302 : : * D=[4/2] {A__D} {_B_D} {__CD} {___D}
303 : : *
304 : : *
305 : : * We implement this tree walk in the following algorithm:
306 : : * 1. Add `next_utxo`
307 : : * 2. Evaluate candidate input set
308 : : * 3. Determine `next_utxo` by deciding whether to
309 : : * a) EXPLORE: Add next inclusion branch, e.g. {_B} ⇒ {_B} + `next_uxto`: C
310 : : * b) SHIFT: Replace last selected UTXO by next higher index, e.g. {A_C} ⇒ {A__} + `next_utxo`: D
311 : : * c) CUT: deselect last selected UTXO and shift to omission branch of penultimate UTXO, e.g. {AB_D} ⇒ {A_} + `next_utxo: C
312 : : *
313 : : * The implementation then adds further optimizations by discovering further situations in which either the inclusion
314 : : * branch can be skipped, or both the inclusion and omission branch can be skipped after evaluating the candidate input
315 : : * set in the node.
316 : : *
317 : : * @param std::vector<OutputGroup>& utxo_pool The UTXOs that we are choosing from. These UTXOs will be sorted in
318 : : * descending order by effective value, with lower weight preferred as a tie-breaker. (We can think of an output
319 : : * group with multiple as a heavier UTXO with the combined amount here.)
320 : : * @param const CAmount& selection_target This is the minimum amount that we need for the transaction without considering change.
321 : : * @param const CAmount& change_target The minimum budget for creating a change output, by which we increase the selection_target.
322 : : * @param int max_selection_weight The maximum allowed weight for a selection result to be valid.
323 : : * @returns The result of this coin selection algorithm, or std::nullopt
324 : : */
325 : 7 : util::Result<SelectionResult> CoinGrinder(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, CAmount change_target, int max_selection_weight)
326 : : {
327 : 7 : std::sort(utxo_pool.begin(), utxo_pool.end(), descending_effval_weight);
328 : : // The sum of UTXO amounts after this UTXO index, e.g. lookahead[5] = Σ(UTXO[6+].amount)
329 : 7 : std::vector<CAmount> lookahead(utxo_pool.size());
330 : : // The minimum UTXO weight among the remaining UTXOs after this UTXO index, e.g. min_tail_weight[5] = min(UTXO[6+].weight)
331 [ + - ]: 7 : std::vector<int> min_tail_weight(utxo_pool.size());
332 : :
333 : : // Calculate lookahead values, min_tail_weights, and check that there are sufficient funds
334 : 7 : CAmount total_available = 0;
335 : 7 : int min_group_weight = std::numeric_limits<int>::max();
336 [ + + ]: 642 : for (size_t i = 0; i < utxo_pool.size(); ++i) {
337 : 635 : size_t index = utxo_pool.size() - 1 - i; // Loop over every element in reverse order
338 [ + - ]: 635 : lookahead[index] = total_available;
339 : 635 : min_tail_weight[index] = min_group_weight;
340 : : // UTXOs with non-positive effective value must have been filtered
341 [ + - + - ]: 635 : Assume(utxo_pool[index].GetSelectionAmount() > 0);
342 [ + - ]: 635 : total_available += utxo_pool[index].GetSelectionAmount();
343 [ + + ]: 1263 : min_group_weight = std::min(min_group_weight, utxo_pool[index].m_weight);
344 : : }
345 : :
346 : 7 : const CAmount total_target = selection_target + change_target;
347 [ + + ]: 7 : if (total_available < total_target) {
348 : : // Insufficient funds
349 : 2 : return util::Error();
350 : : }
351 : :
352 : : // The current selection and the best input set found so far, stored as the utxo_pool indices of the UTXOs forming them
353 : 6 : std::vector<size_t> curr_selection;
354 : 6 : std::vector<size_t> best_selection;
355 : :
356 : : // The currently selected effective amount, and the effective amount of the best selection so far
357 : 6 : CAmount curr_amount = 0;
358 : 6 : CAmount best_selection_amount = MAX_MONEY;
359 : :
360 : : // The weight of the currently selected input set, and the weight of the best selection
361 : 6 : int curr_weight = 0;
362 : 6 : int best_selection_weight = max_selection_weight; // Tie is fine, because we prefer lower selection amount
363 : :
364 : : // Whether the input sets generated during this search have exceeded the maximum transaction weight at any point
365 : 6 : bool max_tx_weight_exceeded = false;
366 : :
367 : : // Index of the next UTXO to consider in utxo_pool
368 : 6 : size_t next_utxo = 0;
369 : :
370 : : /*
371 : : * You can think of the current selection as a vector of booleans that has decided inclusion or exclusion of all
372 : : * UTXOs before `next_utxo`. When we consider the next UTXO, we extend this hypothetical boolean vector either with
373 : : * a true value if the UTXO is included or a false value if it is omitted. The equivalent state is stored more
374 : : * compactly as the list of indices of the included UTXOs and the `next_utxo` index.
375 : : *
376 : : * We can never find a new solution by deselecting a UTXO, because we then revisit a previously evaluated
377 : : * selection. Therefore, we only need to check whether we found a new solution _after adding_ a new UTXO.
378 : : *
379 : : * Each iteration of CoinGrinder starts by selecting the `next_utxo` and evaluating the current selection. We
380 : : * use three state transitions to progress from the current selection to the next promising selection:
381 : : *
382 : : * - EXPLORE inclusion branch: We do not have sufficient funds, yet. Add `next_utxo` to the current selection, then
383 : : * nominate the direct successor of the just selected UTXO as our `next_utxo` for the
384 : : * following iteration.
385 : : *
386 : : * Example:
387 : : * Current Selection: {0, 5, 7}
388 : : * Evaluation: EXPLORE, next_utxo: 8
389 : : * Next Selection: {0, 5, 7, 8}
390 : : *
391 : : * - SHIFT to omission branch: Adding more UTXOs to the current selection cannot produce a solution that is better
392 : : * than the current best, e.g. the current selection weight exceeds the max weight or
393 : : * the current selection amount is equal to or greater than the target.
394 : : * We designate our `next_utxo` the one after the tail of our current selection, then
395 : : * deselect the tail of our current selection.
396 : : *
397 : : * Example:
398 : : * Current Selection: {0, 5, 7}
399 : : * Evaluation: SHIFT, next_utxo: 8, omit last selected: {0, 5}
400 : : * Next Selection: {0, 5, 8}
401 : : *
402 : : * - CUT entire subtree: We have exhausted the inclusion branch for the penultimately selected UTXO, both the
403 : : * inclusion and the omission branch of the current prefix are barren. E.g. we have
404 : : * reached the end of the UTXO pool, so neither further EXPLORING nor SHIFTING can find
405 : : * any solutions. We designate our `next_utxo` the one after our penultimate selected,
406 : : * then deselect both the last and penultimate selected.
407 : : *
408 : : * Example:
409 : : * Current Selection: {0, 5, 7}
410 : : * Evaluation: CUT, next_utxo: 6, omit two last selected: {0}
411 : : * Next Selection: {0, 6}
412 : : */
413 : 205 : auto deselect_last = [&]() {
414 : 199 : OutputGroup& utxo = utxo_pool[curr_selection.back()];
415 : 199 : curr_amount -= utxo.GetSelectionAmount();
416 : 199 : curr_weight -= utxo.m_weight;
417 : 199 : curr_selection.pop_back();
418 : 205 : };
419 : :
420 : 6 : SelectionResult result(selection_target, SelectionAlgorithm::CG);
421 : 6 : bool is_done = false;
422 : 6 : size_t curr_try = 0;
423 : 6 : while (!is_done) {
424 : 199 : bool should_shift{false}, should_cut{false};
425 : : // Select `next_utxo`
426 [ + - ]: 199 : OutputGroup& utxo = utxo_pool[next_utxo];
427 [ + - ]: 199 : curr_amount += utxo.GetSelectionAmount();
428 : 199 : curr_weight += utxo.m_weight;
429 [ + - ]: 199 : curr_selection.push_back(next_utxo);
430 : 199 : ++next_utxo;
431 : 199 : ++curr_try;
432 : :
433 : : // EVALUATE current selection: check for solutions and see whether we can CUT or SHIFT before EXPLORING further
434 : 199 : auto curr_tail = curr_selection.back();
435 [ + + ]: 199 : if (curr_amount + lookahead[curr_tail] < total_target) {
436 : : // Insufficient funds with lookahead: CUT
437 : : should_cut = true;
438 [ + + ]: 176 : } else if (curr_weight > best_selection_weight) {
439 : : // best_selection_weight is initialized to max_selection_weight
440 [ + + ]: 48 : if (curr_weight > max_selection_weight) max_tx_weight_exceeded = true;
441 : : // Worse weight than best solution. More UTXOs only increase weight:
442 : : // CUT if last selected group had minimal weight, else SHIFT
443 [ + + ]: 48 : if (utxo_pool[curr_tail].m_weight <= min_tail_weight[curr_tail]) {
444 : : should_cut = true;
445 : : } else {
446 : 47 : should_shift = true;
447 : : }
448 [ + + ]: 128 : } else if (curr_amount >= total_target) {
449 : : // Success, adding more weight cannot be better: SHIFT
450 : 37 : should_shift = true;
451 [ + + + - : 37 : if (curr_weight < best_selection_weight || (curr_weight == best_selection_weight && curr_amount < best_selection_amount)) {
+ + ]
452 : : // New lowest weight, or same weight with fewer funds tied up
453 [ + - ]: 29 : best_selection = curr_selection;
454 : 29 : best_selection_weight = curr_weight;
455 : 29 : best_selection_amount = curr_amount;
456 : : }
457 [ + + + - : 91 : } else if (!best_selection.empty() && curr_weight + int64_t{min_tail_weight[curr_tail]} * ((total_target - curr_amount + utxo_pool[curr_tail].GetSelectionAmount() - 1) / utxo_pool[curr_tail].GetSelectionAmount()) > best_selection_weight) {
+ - + + ]
458 : : // Compare minimal tail weight and last selected amount with the amount missing to gauge whether a better weight is still possible.
459 [ + + ]: 30 : if (utxo_pool[curr_tail].m_weight <= min_tail_weight[curr_tail]) {
460 : : should_cut = true;
461 : : } else {
462 : 9 : should_shift = true;
463 : : }
464 : : }
465 : :
466 [ - + ]: 199 : if (curr_try >= TOTAL_TRIES) {
467 : : // Solution is not guaranteed to be optimal if `curr_try` hit TOTAL_TRIES
468 [ # # ]: 0 : result.SetAlgoCompleted(false);
469 : : break;
470 : : }
471 : :
472 [ + + ]: 199 : if (next_utxo == utxo_pool.size()) {
473 : : // Last added UTXO was end of UTXO pool, nothing left to add on inclusion or omission branch: CUT
474 : : should_cut = true;
475 : : }
476 : :
477 [ + + ]: 191 : if (should_cut) {
478 : : // Neither adding to the current selection nor exploring the omission branch of the last selected UTXO can
479 : : // find any solutions. Redirect to exploring the Omission branch of the penultimate selected UTXO (i.e.
480 : : // set `next_utxo` to one after the penultimate selected, then deselect the last two selected UTXOs)
481 : 48 : should_cut = false;
482 [ + - ]: 48 : deselect_last();
483 : : should_shift = true;
484 : : }
485 : :
486 [ + + ]: 350 : while (should_shift) {
487 : : // Set `next_utxo` to one after last selected, then deselect last selected UTXO
488 [ + + ]: 157 : if (curr_selection.empty()) {
489 : : // Exhausted search space before running into attempt limit
490 : 6 : is_done = true;
491 [ + - ]: 6 : result.SetAlgoCompleted(true);
492 : : break;
493 : : }
494 : 151 : next_utxo = curr_selection.back() + 1;
495 [ + - ]: 151 : deselect_last();
496 : 2483 : should_shift = false;
497 : :
498 : : // After SHIFTing to an omission branch, the `next_utxo` might have the same effective value as the UTXO we
499 : : // just omitted. Since lower weight is our tiebreaker on UTXOs with equal effective value for sorting, if it
500 : : // ties on the effective value, it _must_ have the same weight (i.e. be a "clone" of the prior UTXO) or a
501 : : // higher weight. If so, selecting `next_utxo` would produce an equivalent or worse selection as one we
502 : : // previously evaluated. In that case, increment `next_utxo` until we find a UTXO with a differing amount.
503 [ + - + - : 2483 : while (utxo_pool[next_utxo - 1].GetSelectionAmount() == utxo_pool[next_utxo].GetSelectionAmount()) {
+ + ]
504 [ + + ]: 2351 : if (next_utxo >= utxo_pool.size() - 1) {
505 : : // Reached end of UTXO pool skipping clones: SHIFT instead
506 : : should_shift = true;
507 : : break;
508 : : }
509 : : // Skip clone: previous UTXO is equivalent and unselected
510 : 2332 : ++next_utxo;
511 : : }
512 : : }
513 : : }
514 : :
515 [ + - ]: 6 : result.SetSelectionsEvaluated(curr_try);
516 : :
517 [ + + ]: 6 : if (best_selection.empty()) {
518 [ + - + - ]: 1 : return max_tx_weight_exceeded ? ErrorMaxWeightExceeded() : util::Error();
519 : : }
520 : :
521 [ + + ]: 43 : for (const size_t& i : best_selection) {
522 [ + - ]: 38 : result.AddInput(utxo_pool[i]);
523 : : }
524 : :
525 : 5 : return result;
526 : 13 : }
527 : :
528 : : class MinOutputGroupComparator
529 : : {
530 : : public:
531 : 542628 : int operator() (const OutputGroup& group1, const OutputGroup& group2) const
532 : : {
533 : 542628 : return group1.GetSelectionAmount() > group2.GetSelectionAmount();
534 : : }
535 : : };
536 : :
537 : 129 : util::Result<SelectionResult> SelectCoinsSRD(const std::vector<OutputGroup>& utxo_pool, CAmount target_value, CAmount change_fee, FastRandomContext& rng,
538 : : int max_selection_weight)
539 : : {
540 [ + - ]: 129 : SelectionResult result(target_value, SelectionAlgorithm::SRD);
541 [ + - ]: 129 : std::priority_queue<OutputGroup, std::vector<OutputGroup>, MinOutputGroupComparator> heap;
542 : :
543 : : // Include change for SRD as we want to avoid making really small change if the selection just
544 : : // barely meets the target. Just use the lower bound change target instead of the randomly
545 : : // generated one, since SRD will result in a random change amount anyway; avoid making the
546 : : // target needlessly large.
547 : 129 : target_value += CHANGE_LOWER + change_fee;
548 : :
549 : 129 : std::vector<size_t> indexes;
550 [ + - ]: 129 : indexes.resize(utxo_pool.size());
551 : 129 : std::iota(indexes.begin(), indexes.end(), 0);
552 : 129 : std::shuffle(indexes.begin(), indexes.end(), rng);
553 : :
554 : 129 : CAmount selected_eff_value = 0;
555 : 129 : int weight = 0;
556 : 129 : bool max_tx_weight_exceeded = false;
557 [ + + ]: 61393 : for (const size_t i : indexes) {
558 [ + - ]: 61376 : const OutputGroup& group = utxo_pool.at(i);
559 [ + - + - ]: 61376 : Assume(group.GetSelectionAmount() > 0);
560 : :
561 : : // Add group to selection
562 [ + - ]: 61376 : heap.push(group);
563 [ + - ]: 61376 : selected_eff_value += group.GetSelectionAmount();
564 : 61376 : weight += group.m_weight;
565 : :
566 : : // If the selection weight exceeds the maximum allowed size, remove the least valuable inputs until we
567 : : // are below max weight.
568 [ + + ]: 61376 : if (weight > max_selection_weight) {
569 : 820 : max_tx_weight_exceeded = true; // mark it in case we don't find any useful result.
570 : 820 : do {
571 [ + - ]: 820 : const OutputGroup& to_remove_group = heap.top();
572 [ + - ]: 820 : selected_eff_value -= to_remove_group.GetSelectionAmount();
573 : 820 : weight -= to_remove_group.m_weight;
574 [ + - ]: 820 : heap.pop();
575 [ + - + - : 1640 : } while (!heap.empty() && weight > max_selection_weight);
- + ]
576 : : }
577 : :
578 : : // Now check if we are above the target
579 [ + + ]: 61376 : if (selected_eff_value >= target_value) {
580 : : // Result found, add it.
581 [ + + ]: 51813 : while (!heap.empty()) {
582 [ + - ]: 51701 : result.AddInput(heap.top());
583 [ + - ]: 51701 : heap.pop();
584 : : }
585 : 112 : return result;
586 : : }
587 : : }
588 [ + + + - ]: 27 : return max_tx_weight_exceeded ? ErrorMaxWeightExceeded() : util::Error();
589 : 129 : }
590 : :
591 : : /** Find a subset of the OutputGroups that is at least as large as, but as close as possible to, the
592 : : * target amount; solve subset sum.
593 : : * param@[in] groups OutputGroups to choose from, sorted by value in descending order.
594 : : * param@[in] nTotalLower Total (effective) value of the UTXOs in groups.
595 : : * param@[in] nTargetValue Subset sum target, not including change.
596 : : * param@[out] vfBest Boolean vector representing the subset chosen that is closest to
597 : : * nTargetValue, with indices corresponding to groups. If the ith
598 : : * entry is true, that means the ith group in groups was selected.
599 : : * param@[out] nBest Total amount of subset chosen that is closest to nTargetValue.
600 : : * paramp[in] max_selection_weight The maximum allowed weight for a selection result to be valid.
601 : : * param@[in] iterations Maximum number of tries.
602 : : */
603 : 2924 : static void ApproximateBestSubset(FastRandomContext& insecure_rand, const std::vector<OutputGroup>& groups,
604 : : const CAmount& nTotalLower, const CAmount& nTargetValue,
605 : : std::vector<char>& vfBest, CAmount& nBest, int max_selection_weight, int iterations = 1000)
606 : : {
607 : 2924 : std::vector<char> vfIncluded;
608 : :
609 : : // Worst case "best" approximation is just all of the groups.
610 [ + - ]: 2924 : vfBest.assign(groups.size(), true);
611 : 2924 : nBest = nTotalLower;
612 : :
613 [ + + + + ]: 1736603 : for (int nRep = 0; nRep < iterations && nBest != nTargetValue; nRep++)
614 : : {
615 [ + - ]: 1733679 : vfIncluded.assign(groups.size(), false);
616 : : CAmount nTotal = 0;
617 : : int selected_coins_weight{0};
618 : : bool fReachedTarget = false;
619 [ + + ]: 4354449 : for (int nPass = 0; nPass < 2 && !fReachedTarget; nPass++)
620 : : {
621 [ + + ]: 405351746 : for (unsigned int i = 0; i < groups.size(); i++)
622 : : {
623 : : //The solver here uses a randomized algorithm,
624 : : //the randomness serves no real security purpose but is just
625 : : //needed to prevent degenerate behavior and it is important
626 : : //that the rng is fast. We do not use a constant random sequence,
627 : : //because there may be some privacy improvement by making
628 : : //the selection random.
629 [ + + + + ]: 402730976 : if (nPass == 0 ? insecure_rand.randbool() : !vfIncluded[i])
630 : : {
631 [ + - ]: 201726672 : nTotal += groups[i].GetSelectionAmount();
632 [ + + ]: 201726672 : selected_coins_weight += groups[i].m_weight;
633 [ + + ]: 201726672 : vfIncluded[i] = true;
634 [ + + + + ]: 201726672 : if (nTotal >= nTargetValue && selected_coins_weight <= max_selection_weight) {
635 : 166653130 : fReachedTarget = true;
636 : : // If the total is between nTargetValue and nBest, it's our new best
637 : : // approximation.
638 [ + + ]: 166653130 : if (nTotal < nBest)
639 : : {
640 : 18966 : nBest = nTotal;
641 [ + - ]: 18966 : vfBest = vfIncluded;
642 : : }
643 [ + - ]: 166653130 : nTotal -= groups[i].GetSelectionAmount();
644 : 166653130 : selected_coins_weight -= groups[i].m_weight;
645 : 166653130 : vfIncluded[i] = false;
646 : : }
647 : : }
648 : : }
649 : : }
650 : : }
651 : 2924 : }
652 : :
653 : 5727 : util::Result<SelectionResult> KnapsackSolver(std::vector<OutputGroup>& groups, const CAmount& nTargetValue,
654 : : CAmount change_target, FastRandomContext& rng, int max_selection_weight)
655 : : {
656 : 5727 : SelectionResult result(nTargetValue, SelectionAlgorithm::KNAPSACK);
657 : :
658 : 5727 : bool max_weight_exceeded{false};
659 : : // List of values less than target
660 : 5727 : std::optional<OutputGroup> lowest_larger;
661 : : // Groups with selection amount smaller than the target and any change we might produce.
662 : : // Don't include groups larger than this, because they will only cause us to overshoot.
663 : 5727 : std::vector<OutputGroup> applicable_groups;
664 : 5727 : CAmount nTotalLower = 0;
665 : :
666 : 5727 : std::shuffle(groups.begin(), groups.end(), rng);
667 : :
668 [ + + ]: 597655 : for (const OutputGroup& group : groups) {
669 [ - + ]: 593033 : if (group.m_weight > max_selection_weight) {
670 : 0 : max_weight_exceeded = true;
671 : 0 : continue;
672 : : }
673 [ + - + + ]: 593033 : if (group.GetSelectionAmount() == nTargetValue) {
674 [ + - ]: 1105 : result.AddInput(group);
675 : 1105 : return result;
676 [ + - + + ]: 591928 : } else if (group.GetSelectionAmount() < nTargetValue + change_target) {
677 [ + - ]: 354021 : applicable_groups.push_back(group);
678 [ + - ]: 354021 : nTotalLower += group.GetSelectionAmount();
679 [ + + + - : 237907 : } else if (!lowest_larger || group.GetSelectionAmount() < lowest_larger->GetSelectionAmount()) {
+ - + + ]
680 [ + - ]: 3109 : lowest_larger = group;
681 : : }
682 : : }
683 : :
684 [ + + ]: 4622 : if (nTotalLower == nTargetValue) {
685 [ + + ]: 2403 : for (const auto& group : applicable_groups) {
686 [ + - ]: 1902 : result.AddInput(group);
687 : : }
688 [ + - ]: 501 : if (result.GetWeight() <= max_selection_weight) return result;
689 : 0 : else max_weight_exceeded = true;
690 : :
691 : : // Try something else
692 [ # # ]: 0 : result.Clear();
693 : : }
694 : :
695 [ + + ]: 4121 : if (nTotalLower < nTargetValue) {
696 [ + + ]: 2105 : if (!lowest_larger) {
697 [ - + - - ]: 600 : if (max_weight_exceeded) return ErrorMaxWeightExceeded();
698 : 1200 : return util::Error();
699 : : }
700 [ + - ]: 1505 : result.AddInput(*lowest_larger);
701 : 1505 : return result;
702 : : }
703 : :
704 : : // Solve subset sum by stochastic approximation
705 [ + - ]: 2016 : std::sort(applicable_groups.begin(), applicable_groups.end(), descending);
706 : 2016 : std::vector<char> vfBest;
707 : 2016 : CAmount nBest;
708 : :
709 [ + - ]: 2016 : ApproximateBestSubset(rng, applicable_groups, nTotalLower, nTargetValue, vfBest, nBest, max_selection_weight);
710 [ + + + + ]: 2016 : if (nBest != nTargetValue && nTotalLower >= nTargetValue + change_target) {
711 [ + - ]: 908 : ApproximateBestSubset(rng, applicable_groups, nTotalLower, nTargetValue + change_target, vfBest, nBest, max_selection_weight);
712 : : }
713 : :
714 : : // If we have a bigger coin and (either the stochastic approximation didn't find a good solution,
715 : : // or the next bigger coin is closer), return the bigger coin
716 [ + + ]: 2016 : if (lowest_larger &&
717 [ + + + + : 2016 : ((nBest != nTargetValue && nBest < nTargetValue + change_target) || lowest_larger->GetSelectionAmount() <= nBest)) {
+ + + - +
+ ]
718 [ + - ]: 300 : result.AddInput(*lowest_larger);
719 : : } else {
720 [ + + ]: 344731 : for (unsigned int i = 0; i < applicable_groups.size(); i++) {
721 [ + + ]: 343015 : if (vfBest[i]) {
722 [ + - ]: 137720 : result.AddInput(applicable_groups[i]);
723 : : }
724 : : }
725 : :
726 : : // If the result exceeds the maximum allowed size, return closest UTXO above the target
727 [ + + ]: 1716 : if (result.GetWeight() > max_selection_weight) {
728 : : // No coin above target, nothing to do.
729 [ + + + - ]: 7 : if (!lowest_larger) return ErrorMaxWeightExceeded();
730 : :
731 : : // Return closest UTXO above target
732 [ + - ]: 1 : result.Clear();
733 [ + - ]: 1 : result.AddInput(*lowest_larger);
734 : : }
735 : :
736 [ + - + - ]: 1710 : if (LogAcceptCategory(BCLog::SELECTCOINS, BCLog::Level::Debug)) {
737 [ + - ]: 1710 : std::string log_message{"Coin selection best subset: "};
738 [ + + ]: 335635 : for (unsigned int i = 0; i < applicable_groups.size(); i++) {
739 [ + + ]: 333925 : if (vfBest[i]) {
740 [ + - + - ]: 257260 : log_message += strprintf("%s ", FormatMoney(applicable_groups[i].m_value));
741 : : }
742 : : }
743 [ + - + - : 3420 : LogDebug(BCLog::SELECTCOINS, "%stotal %s\n", log_message, FormatMoney(nBest));
+ - + - ]
744 : 1710 : }
745 : : }
746 [ + - ]: 2010 : Assume(result.GetWeight() <= max_selection_weight);
747 : 2010 : return result;
748 : 5727 : }
749 : :
750 : : /******************************************************************************
751 : :
752 : : OutputGroup
753 : :
754 : : ******************************************************************************/
755 : :
756 : 738673 : void OutputGroup::Insert(const std::shared_ptr<COutput>& output, size_t ancestors, size_t descendants) {
757 : 738673 : m_outputs.push_back(output);
758 : 738673 : auto& coin = *m_outputs.back();
759 : :
760 : 738673 : fee += coin.GetFee();
761 : :
762 [ + + ]: 738673 : coin.long_term_fee = coin.input_bytes < 0 ? 0 : m_long_term_feerate.GetFee(coin.input_bytes);
763 : 738673 : long_term_fee += coin.long_term_fee;
764 : :
765 : 738673 : effective_value += coin.GetEffectiveValue();
766 : :
767 : 738673 : m_from_me &= coin.from_me;
768 : 738673 : m_value += coin.txout.nValue;
769 [ + + ]: 738673 : m_depth = std::min(m_depth, coin.depth);
770 : : // ancestors here express the number of ancestors the new coin will end up having, which is
771 : : // the sum, rather than the max; this will overestimate in the cases where multiple inputs
772 : : // have common ancestors
773 : 738673 : m_ancestors += ancestors;
774 : : // descendants is the count as seen from the top ancestor, not the descendants as seen from the
775 : : // coin itself; thus, this value is counted as the max, not the sum
776 [ + - ]: 738673 : m_descendants = std::max(m_descendants, descendants);
777 : :
778 [ + + ]: 738673 : if (output->input_bytes > 0) {
779 : 7296 : m_weight += output->input_bytes * WITNESS_SCALE_FACTOR;
780 : : }
781 : 738673 : }
782 : :
783 : 988535 : bool OutputGroup::EligibleForSpending(const CoinEligibilityFilter& eligibility_filter) const
784 : : {
785 [ + + ]: 988535 : return m_depth >= (m_from_me ? eligibility_filter.conf_mine : eligibility_filter.conf_theirs)
786 [ + - ]: 987914 : && m_ancestors <= eligibility_filter.max_ancestors
787 [ + + - + ]: 1976449 : && m_descendants <= eligibility_filter.max_descendants;
788 : : }
789 : :
790 : 418604240 : CAmount OutputGroup::GetSelectionAmount() const
791 : : {
792 [ + + ]: 418604240 : return m_subtract_fee_outputs ? m_value : effective_value;
793 : : }
794 : :
795 : 987912 : void OutputGroupTypeMap::Push(const OutputGroup& group, OutputType type, bool insert_positive, bool insert_mixed)
796 : : {
797 [ + - ]: 987912 : if (group.m_outputs.empty()) return;
798 : :
799 : 987912 : Groups& groups = groups_by_type[type];
800 [ + + + + ]: 987912 : if (insert_positive && group.GetSelectionAmount() > 0) {
801 : 987846 : groups.positive_group.emplace_back(group);
802 : 987846 : all_groups.positive_group.emplace_back(group);
803 : : }
804 [ + + ]: 987912 : if (insert_mixed) {
805 : 987870 : groups.mixed_group.emplace_back(group);
806 : 987870 : all_groups.mixed_group.emplace_back(group);
807 : : }
808 : : }
809 : :
810 : 15 : CAmount GenerateChangeTarget(const CAmount payment_value, const CAmount change_fee, FastRandomContext& rng)
811 : : {
812 [ - + ]: 15 : if (payment_value <= CHANGE_LOWER / 2) {
813 : 0 : return change_fee + CHANGE_LOWER;
814 : : } else {
815 : : // random value between 50ksat and min (payment_value * 2, 1milsat)
816 [ - + ]: 15 : const auto upper_bound = std::min(payment_value * 2, CHANGE_UPPER);
817 : 15 : return change_fee + rng.randrange(upper_bound - CHANGE_LOWER) + CHANGE_LOWER;
818 : : }
819 : : }
820 : :
821 : 2 : void SelectionResult::SetBumpFeeDiscount(const CAmount discount)
822 : : {
823 : : // Overlapping ancestry can only lower the fees, not increase them
824 [ - + ]: 2 : assert (discount >= 0);
825 : 2 : bump_fee_group_discount = discount;
826 : 2 : }
827 : :
828 : 468 : void SelectionResult::RecalculateWaste(const CAmount min_viable_change, const CAmount change_cost, const CAmount change_fee)
829 : : {
830 : : // This function should not be called with empty inputs as that would mean the selection failed
831 [ - + ]: 468 : assert(!m_selected_inputs.empty());
832 : :
833 : : // Always consider the cost of spending an input now vs in the future.
834 : 468 : CAmount waste = 0;
835 [ + + ]: 145358 : for (const auto& coin_ptr : m_selected_inputs) {
836 : 144890 : const COutput& coin = *coin_ptr;
837 : 144890 : waste += coin.GetFee() - coin.long_term_fee;
838 : : }
839 : : // Bump fee of whole selection may diverge from sum of individual bump fees
840 : 468 : waste -= bump_fee_group_discount;
841 : :
842 [ + + ]: 468 : if (GetChange(min_viable_change, change_fee)) {
843 : : // if we have a minimum viable amount after deducting fees, account for
844 : : // cost of creating and spending change
845 : 127 : waste += change_cost;
846 : : } else {
847 : : // When we are not making change (GetChange(…) == 0), consider the excess we are throwing away to fees
848 [ + + ]: 341 : CAmount selected_effective_value = m_use_effective ? GetSelectedEffectiveValue() : GetSelectedValue();
849 [ - + ]: 341 : assert(selected_effective_value >= m_target);
850 : 341 : waste += selected_effective_value - m_target;
851 : : }
852 : :
853 : 468 : m_waste = waste;
854 : 468 : }
855 : :
856 : 6 : void SelectionResult::SetAlgoCompleted(bool algo_completed)
857 : : {
858 : 6 : m_algo_completed = algo_completed;
859 : 6 : }
860 : :
861 : 0 : bool SelectionResult::GetAlgoCompleted() const
862 : : {
863 : 0 : return m_algo_completed;
864 : : }
865 : :
866 : 6 : void SelectionResult::SetSelectionsEvaluated(size_t attempts)
867 : : {
868 : 6 : m_selections_evaluated = attempts;
869 : 6 : }
870 : :
871 : 10 : size_t SelectionResult::GetSelectionsEvaluated() const
872 : : {
873 : 10 : return m_selections_evaluated;
874 : : }
875 : :
876 : 148 : CAmount SelectionResult::GetWaste() const
877 : : {
878 : 148 : return *Assert(m_waste);
879 : : }
880 : :
881 : 2875 : CAmount SelectionResult::GetSelectedValue() const
882 : : {
883 : 122500 : return std::accumulate(m_selected_inputs.cbegin(), m_selected_inputs.cend(), CAmount{0}, [](CAmount sum, const auto& coin) { return sum + coin->txout.nValue; });
884 : : }
885 : :
886 : 782 : CAmount SelectionResult::GetSelectedEffectiveValue() const
887 : : {
888 : 237869 : return std::accumulate(m_selected_inputs.cbegin(), m_selected_inputs.cend(), CAmount{0}, [](CAmount sum, const auto& coin) { return sum + coin->GetEffectiveValue(); }) + bump_fee_group_discount;
889 : : }
890 : :
891 : 13 : CAmount SelectionResult::GetTotalBumpFees() const
892 : : {
893 : 26 : return std::accumulate(m_selected_inputs.cbegin(), m_selected_inputs.cend(), CAmount{0}, [](CAmount sum, const auto& coin) { return sum + coin->ancestor_bump_fees; }) - bump_fee_group_discount;
894 : : }
895 : :
896 : 13 : void SelectionResult::Clear()
897 : : {
898 : 13 : m_selected_inputs.clear();
899 [ - + ]: 13 : m_waste.reset();
900 : 13 : m_weight = 0;
901 : 13 : }
902 : :
903 : 221287 : void SelectionResult::AddInput(const OutputGroup& group)
904 : : {
905 : : // As it can fail, combine inputs first
906 : 221287 : InsertInputs(group.m_outputs);
907 : 221287 : m_use_effective = !group.m_subtract_fee_outputs;
908 : :
909 : 221287 : m_weight += group.m_weight;
910 : 221287 : }
911 : :
912 : 2 : void SelectionResult::AddInputs(const std::set<std::shared_ptr<COutput>>& inputs, bool subtract_fee_outputs)
913 : : {
914 : : // As it can fail, combine inputs first
915 : 2 : InsertInputs(inputs);
916 : 2 : m_use_effective = !subtract_fee_outputs;
917 : :
918 : 2 : m_weight += std::accumulate(inputs.cbegin(), inputs.cend(), 0, [](int sum, const auto& coin) {
919 [ + - ]: 4 : return sum + std::max(coin->input_bytes, 0) * WITNESS_SCALE_FACTOR;
920 : : });
921 : 2 : }
922 : :
923 : 2 : void SelectionResult::Merge(const SelectionResult& other)
924 : : {
925 : : // As it can fail, combine inputs first
926 : 2 : InsertInputs(other.m_selected_inputs);
927 : :
928 : 2 : m_target += other.m_target;
929 : 2 : m_use_effective |= other.m_use_effective;
930 [ - + ]: 2 : if (m_algo == SelectionAlgorithm::MANUAL) {
931 : 0 : m_algo = other.m_algo;
932 : : }
933 : :
934 : 2 : m_weight += other.m_weight;
935 : 2 : }
936 : :
937 : 6779 : const std::set<std::shared_ptr<COutput>>& SelectionResult::GetInputSet() const
938 : : {
939 : 6779 : return m_selected_inputs;
940 : : }
941 : :
942 : 15 : std::vector<std::shared_ptr<COutput>> SelectionResult::GetShuffledInputVector() const
943 : : {
944 : 15 : std::vector<std::shared_ptr<COutput>> coins(m_selected_inputs.begin(), m_selected_inputs.end());
945 : 15 : std::shuffle(coins.begin(), coins.end(), FastRandomContext());
946 : 15 : return coins;
947 : : }
948 : :
949 : 216 : bool SelectionResult::operator<(SelectionResult other) const
950 : : {
951 : 216 : Assert(m_waste.has_value());
952 : 216 : Assert(other.m_waste.has_value());
953 : : // As this operator is only used in std::min_element, we want the result that has more inputs when waste are equal.
954 [ + - + + : 216 : return *m_waste < *other.m_waste || (*m_waste == *other.m_waste && m_selected_inputs.size() > other.m_selected_inputs.size());
+ + ]
955 : : }
956 : :
957 : 0 : std::string COutput::ToString() const
958 : : {
959 [ # # # # ]: 0 : return strprintf("COutput(%s, %d, %d) [%s]", outpoint.hash.ToString(), outpoint.n, depth, FormatMoney(txout.nValue));
960 : : }
961 : :
962 : 13 : std::string GetAlgorithmName(const SelectionAlgorithm algo)
963 : : {
964 [ - + - - : 13 : switch (algo)
- - ]
965 : : {
966 : 0 : case SelectionAlgorithm::BNB: return "bnb";
967 : 13 : case SelectionAlgorithm::KNAPSACK: return "knapsack";
968 : 0 : case SelectionAlgorithm::SRD: return "srd";
969 : 0 : case SelectionAlgorithm::CG: return "cg";
970 : 0 : case SelectionAlgorithm::MANUAL: return "manual";
971 : : // No default case to allow for compiler to warn
972 : : }
973 : 0 : assert(false);
974 : : }
975 : :
976 : 481 : CAmount SelectionResult::GetChange(const CAmount min_viable_change, const CAmount change_fee) const
977 : : {
978 : : // change = SUM(inputs) - SUM(outputs) - fees
979 : : // 1) With SFFO we don't pay any fees
980 : : // 2) Otherwise we pay all the fees:
981 : : // - input fees are covered by GetSelectedEffectiveValue()
982 : : // - non_input_fee is included in m_target
983 : : // - change_fee
984 : 481 : const CAmount change = m_use_effective
985 [ + + ]: 481 : ? GetSelectedEffectiveValue() - m_target - change_fee
986 : 31 : : GetSelectedValue() - m_target;
987 : :
988 [ + + ]: 481 : if (change < min_viable_change) {
989 : 345 : return 0;
990 : : }
991 : :
992 : : return change;
993 : : }
994 : :
995 : : } // namespace wallet
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