refac: comments + renaming `ud_index` which is confusiong

pallets/universal-dividend/src/compute_claim_uds.rs

@@ -24,18 +24,22 @@ pub(super) fn compute_claim_uds<Balance: AtLeast32BitUnsigned>(
 ) -> (UdIndex, Balance) {
     let mut total_amount = Zero::zero();
     let mut total_count = 0;
-    for (ud_index, ud_amount) in past_reevals.rev() {
-        if ud_index <= first_ud_index {
+    // We start in reverse order, i.e. the most recent reeval first
+    for (reeval_index, ud_amount) in past_reevals.rev() {
+        // Therefore, if our first UD is above the current reeval index, we have reached our final useful reeval and must break
+        if reeval_index <= first_ud_index {
             let count = current_ud_index - first_ud_index;
             total_amount += Balance::from(count) * ud_amount;
             total_count += count;
             // First unclaimed UD is reached; stop counting now.
             break;
-        } else {
-            let count = current_ud_index - ud_index;
+        }
+        // Otherwise, we consume the full reeval contained UDs
+        else {
+            let count = current_ud_index - reeval_index;
             total_amount += Balance::from(count) * ud_amount;
             total_count += count;
-            current_ud_index = ud_index;
+            current_ud_index = reeval_index;
         }
     }