From 6bb127a12401e51baf85b6fef5ca2514a6cd75a2 Mon Sep 17 00:00:00 2001
From: RunasSudo <runassudo@yingtongli.me>
Date: Thu, 25 Aug 2022 21:49:50 +1000
Subject: [PATCH] Precompute Ballot::has_equal_rankings at parse time

Before: 5.3943 +- 0.0287
After: 5.27661 +- 0.00472
---
 src/election.rs   | 15 +++++++--------
 src/parser/blt.rs |  9 +++++++++
 src/parser/csp.rs |  9 +++++++--
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/src/election.rs b/src/election.rs
index 4c0a54f..2876dfd 100644
--- a/src/election.rs
+++ b/src/election.rs
@@ -71,6 +71,7 @@ impl<N: Number> Election<N> {
 				let new_ballot = Ballot {
 					orig_value: N::one(),
 					preferences: ballot.preferences.clone(),
+					has_equal_rankings: ballot.has_equal_rankings,
 				};
 				normalised_ballots.push(new_ballot);
 				n += &one;
@@ -81,7 +82,7 @@ impl<N: Number> Election<N> {
 	
 	/// Convert ballots with equal rankings to strict-preference "minivoters"
 	pub fn realise_equal_rankings(&mut self) {
-		if !self.ballots.iter().any(|b| b.has_equal_rankings()) {
+		if !self.ballots.iter().any(|b| b.has_equal_rankings) {
 			// No equal rankings
 			return;
 		}
@@ -582,17 +583,14 @@ pub struct Ballot<N> {
 	pub orig_value: N,
 	/// Indexes of candidates preferenced at each level on the ballot
 	pub preferences: Vec<Vec<usize>>,
+	/// Whether multiple candidates are preferenced at the same level
+	pub has_equal_rankings: bool,
 }
 
 impl<N: Number> Ballot<N> {
-	/// Check if this ballot has any equal rankings
-	pub fn has_equal_rankings(&self) -> bool {
-		return self.preferences.iter().any(|p| p.len() > 1);
-	}
-	
 	/// Convert ballot with equal rankings to strict-preference "minivoters"
 	pub fn realise_equal_rankings_into(self, dest: &mut Vec<Ballot<N>>) {
-		if !self.has_equal_rankings() {
+		if !self.has_equal_rankings {
 			dest.push(self);
 			return;
 		}
@@ -631,7 +629,8 @@ impl<N: Number> Ballot<N> {
 		for minivoter in minivoters {
 			dest.push(Ballot {
 				orig_value: weight_each.clone(),
-				preferences: minivoter
+				preferences: minivoter,
+				has_equal_rankings: false,
 			});
 		}
 	}
diff --git a/src/parser/blt.rs b/src/parser/blt.rs
index f0446a4..e01018f 100644
--- a/src/parser/blt.rs
+++ b/src/parser/blt.rs
@@ -38,6 +38,9 @@ pub struct BLTParser<N: Number, I: Iterator<Item=char>> {
 
 	/// Temporary buffer for parsing ballot values
 	ballot_value_buf: String,
+	/// Whether the current ballot has equal preferences
+	ballot_has_equal_rankings: bool,
+	
 	/// Current line number
 	line_no: u32,
 	/// Current column number
@@ -139,6 +142,8 @@ impl<N: Number, I: Iterator<Item=char>> BLTParser<N, I> {
 	
 	/// Parse a ballot
 	fn ballot(&mut self) -> Result<(), ParseError> {
+		self.ballot_has_equal_rankings = false;
+		
 		self.ballot_value()?;
 		
 		self.delimiter_not_nl();
@@ -152,6 +157,8 @@ impl<N: Number, I: Iterator<Item=char>> BLTParser<N, I> {
 				break;
 			} else if self.lookahead() == '=' {
 				// Equal preference
+				self.ballot_has_equal_rankings = true;
+				
 				self.accept();
 				preferences.last_mut().unwrap().push(self.usize()? - 1);
 				self.delimiter_not_nl();
@@ -167,6 +174,7 @@ impl<N: Number, I: Iterator<Item=char>> BLTParser<N, I> {
 		let ballot = Ballot {
 			orig_value: N::parse(&self.ballot_value_buf),
 			preferences,
+			has_equal_rankings: self.ballot_has_equal_rankings,
 		};
 		self.election.ballots.push(ballot);
 		
@@ -376,6 +384,7 @@ impl<N: Number, I: Iterator<Item=char>> BLTParser<N, I> {
 		Self {
 			chars,
 			ballot_value_buf: String::new(),
+			ballot_has_equal_rankings: false,
 			line_no: 1,
 			col_no: 1,
 			num_candidates: 0,
diff --git a/src/parser/csp.rs b/src/parser/csp.rs
index a621909..640a5db 100644
--- a/src/parser/csp.rs
+++ b/src/parser/csp.rs
@@ -95,6 +95,7 @@ pub fn parse_reader<R: Read, N: Number>(reader: R, require_1: bool, require_sequ
 				ballots.push(Ballot {
 					orig_value: value,
 					preferences: vec![],
+					has_equal_rankings: false,
 				});
 				continue;
 			}
@@ -102,17 +103,20 @@ pub fn parse_reader<R: Read, N: Number>(reader: R, require_1: bool, require_sequ
 		
 		let mut sorted_preferences = Vec::with_capacity(preferences.len());
 		let mut last_ranking = None;
+		let mut has_equal_rankings = false;
+		
 		for ranking in unique_rankings {
 			// Filter for preferences at this ranking
 			let prefs_this_ranking: Vec<usize> = preferences.iter()
 				.filter_map(|(r, i)| if *r == ranking { Some(**i) } else { None })
 				.collect();
 			
-			if require_strict_order {
-				if prefs_this_ranking.len() != 1 {
+			if prefs_this_ranking.len() != 1 {
+				if require_strict_order {
 					// Duplicate rankings
 					break;
 				}
+				has_equal_rankings = true;
 			}
 			
 			if require_sequential {
@@ -131,6 +135,7 @@ pub fn parse_reader<R: Read, N: Number>(reader: R, require_1: bool, require_sequ
 		ballots.push(Ballot {
 			orig_value: value,
 			preferences: sorted_preferences,
+			has_equal_rankings,
 		});
 	}