Implement --normalise-ballots

This, with --sum-surplus-transfers, allows us to fully replicate the Scottish STV result

html/index.html

@@ -158,13 +158,15 @@
 							<input type="number" id="txtDP" value="5" min="0" style="width: 3em;">
 						</label>
 					</div>
-					<div class="col-12">
-						<label>
-							Display up to
-							<input type="number" id="txtPPDP" value="2" min="0" style="width: 3em;">
-							d.p.
-						</label>
-					</div>
+					<label class="col-12">
+						Display up to
+						<input type="number" id="txtPPDP" value="2" min="0" style="width: 3em;">
+						d.p.
+					</label>
+					<label class="col-12">
+						<input type="checkbox" id="chkNormaliseBallots">
+						Normalise ballots
+					</label>
 					<div class="col-12 subheading">
 						Count optimisations:
 					</div>

html/index.js

@@ -116,6 +116,7 @@ async function clickCount() {
 		'filePath': filePath,
 		'numbers': document.getElementById('selNumbers').value,
 		'decimals': document.getElementById('txtDP').value,
+		'normaliseBallots': document.getElementById('chkNormaliseBallots').checked,
 	});
 }
 
@@ -301,6 +302,7 @@ function changePreset() {
 		document.getElementById('chkDeferSurpluses').checked = false;
 		document.getElementById('selNumbers').value = 'rational';
 		document.getElementById('txtPPDP').value = '2';
+		document.getElementById('chkNormaliseBallots').checked = false;
 		document.getElementById('chkRoundQuota').checked = false;
 		document.getElementById('chkRoundVotes').checked = false;
 		document.getElementById('chkRoundTVs').checked = false;
@@ -321,6 +323,7 @@ function changePreset() {
 		document.getElementById('selNumbers').value = 'fixed';
 		document.getElementById('txtDP').value = '5';
 		document.getElementById('txtPPDP').value = '5';
+		document.getElementById('chkNormaliseBallots').checked = true;
 		document.getElementById('chkRoundQuota').checked = true;
 		document.getElementById('txtRoundQuota').value = '0';
 		document.getElementById('chkRoundVotes').checked = false;
@@ -343,6 +346,7 @@ function changePreset() {
 		document.getElementById('selNumbers').value = 'fixed';
 		document.getElementById('txtDP').value = '5';
 		document.getElementById('txtPPDP').value = '0';
+		document.getElementById('chkNormaliseBallots').checked = false;
 		document.getElementById('chkRoundQuota').checked = true;
 		document.getElementById('txtRoundQuota').value = '0';
 		document.getElementById('chkRoundVotes').checked = true;
@@ -365,6 +369,7 @@ function changePreset() {
 		document.getElementById('selNumbers').value = 'fixed';
 		document.getElementById('txtDP').value = '5';
 		document.getElementById('txtPPDP').value = '3';
+		document.getElementById('chkNormaliseBallots').checked = false;
 		document.getElementById('chkRoundQuota').checked = true;
 		document.getElementById('txtRoundQuota').value = '3';
 		document.getElementById('chkRoundVotes').checked = true;
@@ -389,6 +394,7 @@ function changePreset() {
 		document.getElementById('selNumbers').value = 'fixed';
 		document.getElementById('txtDP').value = '5';
 		document.getElementById('txtPPDP').value = '2';
+		document.getElementById('chkNormaliseBallots').checked = false;
 		document.getElementById('chkRoundQuota').checked = true;
 		document.getElementById('txtRoundQuota').value = '2';
 		document.getElementById('chkRoundVotes').checked = true;

html/worker.js

@@ -25,6 +25,10 @@ onmessage = function(evt) {
 		// Init election
 		let election = wasm['election_from_blt_' + numbers](evt.data.electionData);
 		
+		if (evt.data.normaliseBallots) {
+			wasm['election_normalise_ballots_' + numbers](election);
+		}
+		
 		// Init STV options
 		let opts = wasm.STVOptions.new.apply(null, evt.data.optsStr);
 		

src/election.rs

@@ -87,6 +87,23 @@ impl<N: Number> Election<N> {
 		
 		return election;
 	}
+	
+	pub fn normalise_ballots(&mut self) {
+		let mut normalised_ballots = Vec::new();
+		for ballot in self.ballots.iter() {
+			let mut n = N::new();
+			let one = N::one();
+			while n < ballot.orig_value {
+				let new_ballot = Ballot {
+					orig_value: N::one(),
+					preferences: ballot.preferences.clone(),
+				};
+				normalised_ballots.push(new_ballot);
+				n += &one;
+			}
+		}
+		self.ballots = normalised_ballots;
+	}
 }
 
 #[derive(PartialEq, Eq, Hash)]

src/main.rs

@@ -59,6 +59,10 @@ struct STV {
 	#[clap(help_heading=Some("NUMBERS"), long, default_value="5", value_name="dps")]
 	decimals: usize,
 	
+	/// Convert ballots with value >1 to multiple ballots of value 1
+	#[clap(help_heading=Some("NUMBERS"), long)]
+	normalise_ballots: bool,
+	
 	// -----------------------
 	// -- Rounding settings --
 	
@@ -164,7 +168,7 @@ fn main() {
 	}
 }
 
-fn count_election<N: Number>(election: Election<N>, cmd_opts: STV)
+fn count_election<N: Number>(mut election: Election<N>, cmd_opts: STV)
 where
 	for<'r> &'r N: ops::Sub<&'r N, Output=N>,
 	for<'r> &'r N: ops::Div<&'r N, Output=N>,
@@ -189,6 +193,11 @@ where
 		cmd_opts.pp_decimals,
 	);
 	
+	// Normalise ballots if requested
+	if cmd_opts.normalise_ballots {
+		election.normalise_ballots();
+	}
+	
 	// Initialise count state
 	let mut state = CountState::new(&election);
 	

src/stv/wasm.rs

@@ -47,6 +47,12 @@ macro_rules! impl_type {
 			return [<Election$type>](election);
 		}
 		
+		#[wasm_bindgen]
+		#[allow(non_snake_case)]
+		pub fn [<election_normalise_ballots_$type>](election: &mut [<Election$type>]) {
+			election.0.normalise_ballots();
+		}
+		
 		#[wasm_bindgen]
 		#[allow(non_snake_case)]
 		pub fn [<count_init_$type>](state: &mut [<CountState$type>], opts: &stv::STVOptions) {

tests/scotland.rs

@@ -69,7 +69,10 @@ fn scotland_linn07_fixed5() {
 	let file_reader = io::BufReader::new(file);
 	let lines = file_reader.lines();
 	
-	let election: Election<Fixed> = Election::from_blt(lines.map(|r| r.expect("IO Error").to_string()).into_iter());
+	let mut election: Election<Fixed> = Election::from_blt(lines.map(|r| r.expect("IO Error").to_string()).into_iter());
+	
+	// !!! FOR SCOTTISH STV !!!
+	election.normalise_ballots();
 	
 	// Initialise count state
 	let mut state = CountState::new(&election);
@@ -87,7 +90,7 @@ fn scotland_linn07_fixed5() {
 			.get_text().unwrap()
 			.to_string();
 		
-		assert!(approx_eq(&(&state.exhausted.votes + &state.loss_fraction.votes), &parse_str(nt_votes)));
+		assert!((&state.exhausted.votes + &state.loss_fraction.votes) == parse_str(nt_votes));
 		
 		for (candidate, cand_xml) in state.election.candidates.iter().zip(candidates.iter()) {
 			let count_card = state.candidates.get(candidate).unwrap();
@@ -98,7 +101,7 @@ fn scotland_linn07_fixed5() {
 				.get_text().unwrap()
 				.to_string();
 			let cand_votes = parse_str(cand_votes);
-			assert!(approx_eq(&count_card.votes, &cand_votes), "Failed to validate votes for candidate {}. Expected {:}, got {:}", candidate.name, cand_votes, count_card.votes);
+			assert!(count_card.votes == cand_votes, "Failed to validate votes for candidate {}. Expected {:}, got {:}", candidate.name, cand_votes, count_card.votes);
 			
 			// Validate candidate states
 			let cand_state = get_cand_stage(cand_xml, i)
@@ -137,17 +140,3 @@ fn parse_str(s: String) -> Fixed {
 	let f: f64 = s.parse().expect("Syntax Error");
 	return opentally::numbers::From::from(f);
 }
-
-fn approx_eq(a: &Fixed, b: &Fixed) -> bool {
-	// Some tolerance required in equality comparisons, as eSTV incorrectly computes transfers
-	// by value, instead of all at once, resulting in increased rounding error
-	let eq_tol: Fixed = opentally::numbers::From::from(0.0001);
-	
-	if a - b > eq_tol {
-		return false;
-	}
-	if b - a > eq_tol {
-		return false;
-	}
-	return true;
-}