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Fold GetSelectionWaste() into ComputeAndSetWaste()

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Both `GetSelectionWaste()` and `ComputeAndSetWaste()` now are part of
`SelectionResult`. Instead of `ComputeAndSetWaste()` being a wrapper for
`GetSelectionWaste()`, we combine them to a new function
`RecalculateWaste()`.

As I was combining the logic of the two functions, I noticed that
`GetSelectionWaste()` was making the odd assumption that the
`change_cost` being set to zero means that no change is created.
However, if we build transactions at a feerate of zero with the
`discard_feerate` also set to zero, we'd organically have a
`change_cost` of zero, even when we create change on a transaction.

This commit cleans up this duplicate meaning of `change_cost` and relies
on `GetChange()` to figure out whether there is change on basis of the
`min_viable_change` and whatever is left after deducting fees.

Since this broke a bunch of tests that relied on the double-meaning of
`change_cost` a bunch of tests had to be fixed.
This commit is contained in:
Murch
2023-08-21 15:27:23 -04:00
parent 5a5ab1d544
commit 7aa7e30441
6 changed files with 83 additions and 99 deletions
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31
src/wallet/coinselection.h
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@@ -350,22 +350,6 @@ private:
}
}
/** 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] change_cost The cost of creating change and spending it in the future.
* Only used if there is change, in which case it must be positive.
* 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(CAmount change_cost, CAmount target, bool use_effective_value = true);
public:
explicit SelectionResult(const CAmount target, SelectionAlgorithm algo)
: m_target(target), m_algo(algo) {}
@@ -387,8 +371,19 @@ public:
/** How much individual inputs overestimated the bump fees for shared ancestries */
void SetBumpFeeDiscount(const CAmount discount);
/** Calculates and stores the waste for this selection via GetSelectionWaste */
void ComputeAndSetWaste(const CAmount min_viable_change, const CAmount change_cost, const CAmount change_fee);
/** Calculates and stores 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) - bump_fee_group_discount
* If no change, waste = excess + inputs * (effective_feerate - long_term_feerate) - bump_fee_group_discount
* where excess = selected_effective_value - target
* change_cost = effective_feerate * change_output_size + long_term_feerate * change_spend_size
*
* @param[in] min_viable_change The minimum amount necessary to make a change output economic
* @param[in] change_cost The cost of creating a change output and spending it in the future. Only
* used if there is change, in which case it must be non-negative.
* @param[in] change_fee The fee for creating a change output
*/
void RecalculateWaste(const CAmount min_viable_change, const CAmount change_cost, const CAmount change_fee);
[[nodiscard]] CAmount GetWaste() const;
/** Tracks that algorithm was able to exhaustively search the entire combination space before hitting limit of tries */