Add requested changes

Author: csralvall

src/wallet/coin_selection.rs

@@ -147,20 +147,20 @@ impl CoinSelectionResult {
 
 /// Metric introduced to measure the performance of different coin selection algorithms.
 ///
-/// This implementations considers waste as the sum of two values:
+/// This implementation considers "waste" the sum of two values:
 /// * Timing cost
 /// * Creation cost
 /// > waste = timing_cost + creation_cost
 ///
-/// **Timing cost** is the cost associated to the current fee rate and some long term fee rate used
-/// as a treshold to consolidate UTXOs.
+/// **Timing cost** is the cost associated with the current fee rate and some long term fee rate used
+/// as a threshold to consolidate UTXOs.
 /// > timing_cost = txin_size * current_fee_rate - txin_size * long_term_fee_rate
 ///
 /// Timing cost can be negative if the `current_fee_rate` is cheaper than the `long_term_fee_rate`,
 /// or zero if they are equal.
 ///
-/// **Creation cost** is the cost associated to the surplus of coins besides the transaction amount
-/// and transaction fees. It can happen in the form of a change output or in the form of excess
+/// **Creation cost** is the cost associated with the surplus of coins beyond the transaction amount
+/// and transaction fees. It can appear in the form of a change output or in the form of excess
 /// fees paid to the miner.
 ///
 /// Change cost is derived from the cost of adding the extra output to the transaction and spending
@@ -177,7 +177,7 @@ impl CoinSelectionResult {
 /// algorithm.
 ///
 /// So, waste can be zero if creation and timing cost are zero. Or can be negative, if timing cost
-/// is negative and the creation cost is lower enough (less than the absolute value of timing
+/// is negative and the creation cost is low enough (less than the absolute value of timing
 /// cost).
 #[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
 pub struct Waste(pub i64);
@@ -189,7 +189,10 @@ impl Waste {
     ///
     /// - `selected`: the selected transaction inputs
     /// - `cost_of_change`: the cost of creating change and spending it in the future
-    /// - `target`: the amount in satoshis of the aimed transaction output
+    /// - `target`: threshold in satoshis used to select UTXOs. It includes the sum of recipient
+    ///             outputs, the fees for creating the recipient outputs and the fees for fixed transaction
+    ///             parts
+
     /// - `fee_rate`: fee rate to use
     pub fn calculate(
         selected: &[WeightedUtxo],
@@ -1511,7 +1514,7 @@ mod test {
         let change_out_size = 31_f32;
         let change_in_size = 68_f32;
         let cost_of_change: u64 = (change_out_size * fee_rate.as_sat_vb()
-            - change_in_size * LONG_TERM_FEE_RATE.as_sat_vb())
+            + change_in_size * LONG_TERM_FEE_RATE.as_sat_vb())
             as u64;
 
         let utxo_fee_diff: i64 = utxos.iter().fold(0, |acc, utxo| {