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Add waste metric calculation function

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Andrew Chow 2021-05-20 19:06:56 -04:00
parent 935b3ddf72
commit 4f5ad43b1e
2 changed files with 42 additions and 0 deletions
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27
src/wallet/coinselection.cpp
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@ -341,3 +341,30 @@ CAmount OutputGroup::GetSelectionAmount() const
{
return m_subtract_fee_outputs ? m_value : effective_value;
}
CAmount GetSelectionWaste(const std::set<CInputCoin>& inputs, CAmount change_cost, CAmount target, bool use_effective_value)
{
// This function should not be called with empty inputs as that would mean the selection failed
assert(!inputs.empty());
// Always consider the cost of spending an input now vs in the future.
CAmount waste = 0;
CAmount selected_effective_value = 0;
for (const CInputCoin& coin : inputs) {
waste += coin.m_fee - coin.m_long_term_fee;
selected_effective_value += use_effective_value ? coin.effective_value : coin.txout.nValue;
}
if (change_cost) {
// Consider the cost of making change and spending it in the future
// If we aren't making change, the caller should've set change_cost to 0
assert(change_cost > 0);
waste += change_cost;
} else {
// When we are not making change (change_cost == 0), consider the excess we are throwing away to fees
assert(selected_effective_value >= target);
waste += selected_effective_value - target;
}
return waste;
}

15
src/wallet/coinselection.h
View file

@ -166,6 +166,21 @@ struct OutputGroup
CAmount GetSelectionAmount() const;
};
/** Compute the waste for this result given the cost of change
* and the opportunity cost of spending these inputs now vs in the future.
* If change exists, waste = change_cost + inputs * (effective_feerate - long_term_feerate)
* If no change, waste = excess + inputs * (effective_feerate - long_term_feerate)
* where excess = selected_effective_value - target
* change_cost = effective_feerate * change_output_size + long_term_feerate * change_spend_size
*
* @param[in] inputs The selected inputs
* @param[in] change_cost The cost of creating change and spending it in the future. Only used if there is change. Must be 0 if there is no change.
* @param[in] target The amount targeted by the coin selection algorithm.
* @param[in] use_effective_value Whether to use the input's effective value (when true) or the real value (when false).
* @return The waste
*/
[[nodiscard]] CAmount GetSelectionWaste(const std::set<CInputCoin>& inputs, CAmount change_cost, CAmount target, bool use_effective_value = true);
bool SelectCoinsBnB(std::vector<OutputGroup>& utxo_pool, const CAmount& selection_target, const CAmount& cost_of_change, std::set<CInputCoin>& out_set, CAmount& value_ret);
// Original coin selection algorithm as a fallback