From c140ef0a9005fb1df823507e8939d662285047d1 Mon Sep 17 00:00:00 2001
From: RunasSudo <runassudo@yingtongli.me>
Date: Sun, 11 Jun 2023 21:01:29 +1000
Subject: [PATCH] Fix rounding of subtransfers by parcel

Was erroneously segmenting transfers by outgoing parcel rather than incoming parcel
---
 src/stv/gregory/mod.rs | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/src/stv/gregory/mod.rs b/src/stv/gregory/mod.rs
index eda06df..9528f80 100644
--- a/src/stv/gregory/mod.rs
+++ b/src/stv/gregory/mod.rs
@@ -241,7 +241,7 @@ where
 	let mut exhausted_ballots = N::new();
 	let mut exhausted_votes = N::new();
 	
-	for parcel in parcels {
+	for (parcel_num, parcel) in parcels.into_iter().enumerate() {
 		// Count next preferences
 		let result = super::next_preferences(state, parcel.votes);
 		
@@ -253,7 +253,14 @@ where
 		exhausted_ballots += &result.exhausted.num_ballots;
 		exhausted_votes += &result.exhausted.num_ballots * &parcel.value_fraction;
 		
-		parcels_next_prefs.push((parcel.value_fraction, parcel.source_order, result));
+		// Determine which column of the transfer table to use
+		let table_column_num = match opts.round_subtransfers {
+			RoundSubtransfersMode::ByValueAndSource => Some(parcel.source_order),
+			RoundSubtransfersMode::ByParcel => Some(parcel_num),
+			_ => Some(0)
+		};
+		
+		parcels_next_prefs.push((parcel.value_fraction, table_column_num, result));
 	}
 	
 	// Calculate and print surplus fraction
@@ -320,16 +327,12 @@ where
 		surplus.clone(), surplus_fraction.clone(), surplus_numer.clone(), surplus_denom.clone()
 	);
 	
-	for (value_fraction, source_order, result) in parcels_next_prefs {
+	for (value_fraction, table_column_num, result) in parcels_next_prefs {
 		for (candidate, entry) in result.candidates.into_iter() {
 			// Record transfers
 			transfer_table.add_transfers(
 				&value_fraction,
-				match opts.round_subtransfers {
-					RoundSubtransfersMode::ByValueAndSource => Some(source_order),
-					RoundSubtransfersMode::ByParcel => None, // Force new column per parcel
-					_ => Some(0)
-				},
+				table_column_num,
 				candidate,
 				&entry.num_ballots
 			);
@@ -366,11 +369,7 @@ where
 		// Record exhausted votes
 		transfer_table.add_exhausted(
 			&value_fraction,
-			match opts.round_subtransfers {
-				RoundSubtransfersMode::ByValueAndSource => Some(source_order),
-				RoundSubtransfersMode::ByParcel => None, // Force new column per parcel
-				_ => Some(0)
-			},
+			table_column_num,
 			&result.exhausted.num_ballots
 		);