Fix incorrect crediting of votes when surplus votes transferred at values received

Many thanks to J Groves for pointing this out

src/stv/gregory/transfers.rs

@@ -202,7 +202,8 @@ impl<'e, N: Number> TransferTable<'e, N> {
 		if self.surplus.is_none() || opts.sum_surplus_transfers == SumSurplusTransfersMode::ByValue {
 			for (_candidate, cell) in self.total.cells.iter_mut() {
 				let mut votes_out;
-				if is_weighted {
+				if is_weighted || self.surpfrac.is_none() {
+					// NB: If surplus.is_none, then votes transferred at values received
 					votes_out = cell.votes_in.clone();
 				} else {
 					votes_out = cell.ballots.clone();
@@ -221,7 +222,7 @@ impl<'e, N: Number> TransferTable<'e, N> {
 			
 			if self.surplus.is_none() || !opts.transferable_only {
 				let mut votes_out;
-				if is_weighted {
+				if is_weighted || self.surpfrac.is_none() {
 					votes_out = self.total.exhausted.votes_in.clone();
 				} else {
 					votes_out = self.total.exhausted.ballots.clone();

tests/data/surplus_values_received.blt

@@ -0,0 +1,13 @@
+# Comment: Constructed example - surplus votes need to be transferred at values received
+4 3
+12 1 2 0
+3 1 2 3 0  # These votes need to be transferred to C at values received by B
+9 2 0
+8 3 0
+7 4 0
+0
+"A"
+"B"
+"C"
+"D"
+"Surplus transferred at values received"

tests/data/surplus_values_received.csv

@@ -0,0 +1,7 @@
+Stage:,1,,2,,3,
+Comment:,First preferences,,Surplus of A,,Surplus of B,
+A,15,EL,9.75,EL,9.75,EL
+B,9,H,14.25,EL,9.75,EL
+C,8,H,8,H,9.05,EL
+D,7,H,7,H,7,H
+Exhausted,0,,0,,3.45,

tests/tests_impl/special_cases.rs

@@ -15,8 +15,10 @@
  *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+use crate::utils;
+
 use opentally::election::{CandidateState, CountState, Election};
-use opentally::numbers::Rational;
+use opentally::numbers::{Fixed, Rational};
 use opentally::parser::blt;
 use opentally::stv;
 use opentally::ties::TieStrategy;
@@ -146,3 +148,28 @@ fn tideman_a34_prsa1977_rational() {
 	
 	// Assert count completes
 }
+
+/// Surplus votes need to be transferred at values received
+#[test]
+fn surplus_values_received() {
+	let stv_opts = stv::STVOptionsBuilder::default()
+		.round_surplus_fractions(Some(2))
+		.round_values(Some(2))
+		.round_votes(Some(2))
+		.round_quota(Some(2))
+		.quota(stv::QuotaType::DroopExact)
+		.quota_criterion(stv::QuotaCriterion::GreaterOrEqual)
+		.quota_mode(stv::QuotaMode::ERS97)
+		.surplus(stv::SurplusMethod::EG)
+		.transferable_only(true)
+		.exclusion(stv::ExclusionMethod::ByValue)
+		.bulk_exclude(true)
+		.defer_surpluses(true)
+		.build().unwrap();
+	
+	Fixed::set_dps(5);
+	
+	assert_eq!(stv_opts.describe::<Fixed>(), "--numbers fixed --decimals 5 --round-surplus-fractions 2 --round-values 2 --round-votes 2 --round-quota 2 --quota droop_exact --quota-criterion geq --quota-mode ers97 --surplus eg --transferable-only --exclusion by_value --bulk-exclude --defer-surpluses");
+	
+	utils::read_validate_election::<Fixed>("tests/data/surplus_values_received.csv", "tests/data/surplus_values_received.blt", stv_opts, None, &["exhausted"]);
+}