1091 lines
35 KiB
Rust
1091 lines
35 KiB
Rust
/* OpenTally: Open-source election vote counting
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* Copyright © 2021 Lee Yingtong Li (RunasSudo)
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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#![allow(mutable_borrow_reservation_conflict)]
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/// Gregory method of surplus distributions
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pub mod gregory;
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/// Meek method of surplus distributions, etc.
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pub mod meek;
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/// WebAssembly wrappers
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//#[cfg(target_arch = "wasm32")]
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pub mod wasm;
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use crate::numbers::Number;
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use crate::election::{Candidate, CandidateState, CountCard, CountState, Vote};
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use crate::sharandom::SHARandom;
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use crate::ties::TieStrategy;
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use itertools::Itertools;
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use wasm_bindgen::prelude::wasm_bindgen;
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use std::collections::HashMap;
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use std::ops;
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/// Options for conducting an STV count
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pub struct STVOptions {
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/// Round transfer values to specified decimal places
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pub round_tvs: Option<usize>,
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/// Round ballot weights to specified decimal places
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pub round_weights: Option<usize>,
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/// Round votes to specified decimal places
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pub round_votes: Option<usize>,
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/// Round quota to specified decimal places
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pub round_quota: Option<usize>,
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/// How to calculate votes to credit to candidates in surplus transfers
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pub sum_surplus_transfers: SumSurplusTransfersMode,
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/// Convert ballots with value >1 to multiple ballots of value 1
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pub normalise_ballots: bool,
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/// Quota type
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pub quota: QuotaType,
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/// Whether to elect candidates on meeting (geq) or strictly exceeding (gt) the quota
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pub quota_criterion: QuotaCriterion,
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/// Whether to apply a form of progressive quota
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pub quota_mode: QuotaMode,
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/// Tie-breaking method
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pub ties: Vec<TieStrategy>,
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/// Method of surplus distributions
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pub surplus: SurplusMethod,
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/// Order to distribute surpluses
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pub surplus_order: SurplusOrder,
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/// Examine only transferable papers during surplus distributions
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pub transferable_only: bool,
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/// Method of exclusions
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pub exclusion: ExclusionMethod,
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/// Use bulk exclusion
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pub bulk_exclude: bool,
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/// Defer surplus distributions if possible
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pub defer_surpluses: bool,
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/// Print votes to specified decimal places in results report
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pub pp_decimals: usize,
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}
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impl STVOptions {
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/// Returns a new [STVOptions] based on arguments given as strings
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pub fn new(
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round_tvs: Option<usize>,
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round_weights: Option<usize>,
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round_votes: Option<usize>,
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round_quota: Option<usize>,
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sum_surplus_transfers: &str,
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normalise_ballots: bool,
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quota: &str,
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quota_criterion: &str,
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quota_mode: &str,
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ties: &Vec<String>,
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random_seed: &Option<String>,
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surplus: &str,
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surplus_order: &str,
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transferable_only: bool,
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exclusion: &str,
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bulk_exclude: bool,
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defer_surpluses: bool,
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pp_decimals: usize,
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) -> Self {
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return STVOptions {
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round_tvs,
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round_weights,
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round_votes,
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round_quota,
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sum_surplus_transfers: match sum_surplus_transfers {
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"single_step" => SumSurplusTransfersMode::SingleStep,
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"by_value" => SumSurplusTransfersMode::ByValue,
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"per_ballot" => SumSurplusTransfersMode::PerBallot,
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_ => panic!("Invalid --sum-transfers"),
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},
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normalise_ballots,
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quota: match quota {
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"droop" => QuotaType::Droop,
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"hare" => QuotaType::Hare,
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"droop_exact" => QuotaType::DroopExact,
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"hare_exact" => QuotaType::HareExact,
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_ => panic!("Invalid --quota"),
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},
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quota_criterion: match quota_criterion {
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"geq" => QuotaCriterion::GreaterOrEqual,
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"gt" => QuotaCriterion::Greater,
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_ => panic!("Invalid --quota-criterion"),
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},
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quota_mode: match quota_mode {
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"static" => QuotaMode::Static,
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"ers97" => QuotaMode::ERS97,
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_ => panic!("Invalid --quota-mode"),
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},
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ties: ties.into_iter().map(|t| match t.as_str() {
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"forwards" => TieStrategy::Forwards,
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"backwards" => TieStrategy::Backwards,
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"random" => TieStrategy::Random(random_seed.as_ref().expect("Must provide a --random-seed if using --ties random").clone()),
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"prompt" => TieStrategy::Prompt,
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_ => panic!("Invalid --ties"),
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}).collect(),
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surplus: match surplus {
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"wig" => SurplusMethod::WIG,
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"uig" => SurplusMethod::UIG,
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"eg" => SurplusMethod::EG,
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"meek" => SurplusMethod::Meek,
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_ => panic!("Invalid --surplus"),
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},
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surplus_order: match surplus_order {
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"by_size" => SurplusOrder::BySize,
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"by_order" => SurplusOrder::ByOrder,
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_ => panic!("Invalid --surplus-order"),
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},
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transferable_only,
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exclusion: match exclusion {
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"single_stage" => ExclusionMethod::SingleStage,
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"by_value" => ExclusionMethod::ByValue,
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"parcels_by_order" => ExclusionMethod::ParcelsByOrder,
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_ => panic!("Invalid --exclusion"),
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},
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bulk_exclude,
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defer_surpluses,
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pp_decimals,
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};
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}
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/// Converts the [STVOptions] into CLI argument representation
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pub fn describe<N: Number>(&self) -> String {
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let mut flags = Vec::new();
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let n_str = N::describe_opt(); if !n_str.is_empty() { flags.push(N::describe_opt()) };
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if let Some(dps) = self.round_tvs { flags.push(format!("--round-tvs {}", dps)); }
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if let Some(dps) = self.round_weights { flags.push(format!("--round-weights {}", dps)); }
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if let Some(dps) = self.round_votes { flags.push(format!("--round-votes {}", dps)); }
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if let Some(dps) = self.round_quota { flags.push(format!("--round-quota {}", dps)); }
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if self.sum_surplus_transfers != SumSurplusTransfersMode::SingleStep { flags.push(self.sum_surplus_transfers.describe()); }
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if self.normalise_ballots { flags.push("--normalise-ballots".to_string()); }
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let ties_str = self.ties.iter().map(|t| t.describe()).join(" ");
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if ties_str != "prompt" { flags.push(format!("--ties {}", ties_str)); }
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for t in self.ties.iter() { if let TieStrategy::Random(seed) = t { flags.push(format!("--random-seed {}", seed)); } }
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if self.quota != QuotaType::DroopExact { flags.push(self.quota.describe()); }
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if self.quota_criterion != QuotaCriterion::Greater { flags.push(self.quota_criterion.describe()); }
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if self.quota_mode != QuotaMode::Static { flags.push(self.quota_mode.describe()); }
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if self.surplus != SurplusMethod::WIG { flags.push(self.surplus.describe()); }
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if self.surplus_order != SurplusOrder::BySize { flags.push(self.surplus_order.describe()); }
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if self.transferable_only { flags.push("--transferable-only".to_string()); }
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if self.exclusion != ExclusionMethod::SingleStage { flags.push(self.exclusion.describe()); }
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if self.bulk_exclude { flags.push("--bulk-exclude".to_string()); }
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if self.defer_surpluses { flags.push("--defer-surpluses".to_string()); }
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if self.pp_decimals != 2 { flags.push(format!("--pp-decimals {}", self.pp_decimals)); }
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return flags.join(" ");
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}
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}
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/// Enum of options for [STVOptions::sum_surplus_transfers]
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#[wasm_bindgen]
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#[derive(Clone, Copy)]
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#[derive(PartialEq)]
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pub enum SumSurplusTransfersMode {
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/// Sum and round all surplus transfers for a candidate in a single step
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SingleStep,
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/// Sum and round a candidate's surplus transfers separately for ballot papers received at each particular value
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ByValue,
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/// Sum and round a candidate's surplus transfers individually for each ballot paper
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PerBallot,
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}
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impl SumSurplusTransfersMode {
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/// Convert to CLI argument representation
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fn describe(self) -> String {
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match self {
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SumSurplusTransfersMode::SingleStep => "--sum-surplus-transfers single_step",
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SumSurplusTransfersMode::ByValue => "--sum-surplus-transfers by_value",
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SumSurplusTransfersMode::PerBallot => "--sum-surplus-transfers per_ballot",
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}.to_string()
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}
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}
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/// Enum of options for [STVOptions::quota]
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#[wasm_bindgen]
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#[derive(Clone, Copy)]
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#[derive(PartialEq)]
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pub enum QuotaType {
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/// Droop quota
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Droop,
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/// Hare quota
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Hare,
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/// Exact Droop quota (Newland–Britton/Hagenbach-Bischoff quota)
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DroopExact,
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/// Exact Hare quota
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HareExact,
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}
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impl QuotaType {
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/// Convert to CLI argument representation
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fn describe(self) -> String {
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match self {
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QuotaType::Droop => "--quota droop",
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QuotaType::Hare => "--quota hare",
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QuotaType::DroopExact => "--quota droop_exact",
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QuotaType::HareExact => "--quota hare_exact",
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}.to_string()
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}
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}
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/// Enum of options for [STVOptions::quota_criterion]
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#[wasm_bindgen]
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#[derive(Clone, Copy)]
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#[derive(PartialEq)]
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pub enum QuotaCriterion {
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/// Elect candidates on equalling or exceeding the quota
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GreaterOrEqual,
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/// Elect candidates on strictly exceeding the quota
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Greater,
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}
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impl QuotaCriterion {
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/// Convert to CLI argument representation
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fn describe(self) -> String {
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match self {
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QuotaCriterion::GreaterOrEqual => "--quota-criterion geq",
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QuotaCriterion::Greater => "--quota-criterion gt",
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}.to_string()
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}
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}
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/// Enum of options for [STVOptions::quota_mode]
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#[wasm_bindgen]
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#[derive(Clone, Copy)]
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#[derive(PartialEq)]
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pub enum QuotaMode {
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/// Static quota
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Static,
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/// Static quota with ERS97 rules
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ERS97,
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}
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impl QuotaMode {
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/// Convert to CLI argument representation
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fn describe(self) -> String {
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match self {
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QuotaMode::Static => "--quota-mode static",
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QuotaMode::ERS97 => "--quota-mode ers97",
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}.to_string()
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}
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}
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/// Enum of options for [STVOptions::surplus]
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#[wasm_bindgen]
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#[derive(Clone, Copy)]
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#[derive(PartialEq)]
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pub enum SurplusMethod {
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/// Weighted inclusive Gregory method
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WIG,
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/// Unweighted inclusive Gregory method
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UIG,
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/// Exclusive Gregory method (last bundle)
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EG,
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/// Meek method
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Meek,
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}
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impl SurplusMethod {
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/// Convert to CLI argument representation
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fn describe(self) -> String {
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match self {
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SurplusMethod::WIG => "--surplus wig",
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SurplusMethod::UIG => "--surplus uig",
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SurplusMethod::EG => "--surplus eg",
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SurplusMethod::Meek => "--surplus meek",
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}.to_string()
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}
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}
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/// Enum of options for [STVOptions::surplus_order]
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#[wasm_bindgen]
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#[derive(Clone, Copy)]
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#[derive(PartialEq)]
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pub enum SurplusOrder {
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/// Transfer the largest surplus first, even if it arose at a later stage of the count
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BySize,
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/// Transfer the surplus of the candidate elected first, even if it is smaller than another
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ByOrder,
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}
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impl SurplusOrder {
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/// Convert to CLI argument representation
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fn describe(self) -> String {
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match self {
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SurplusOrder::BySize => "--surplus-order by_size",
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SurplusOrder::ByOrder => "--surplus-order by_order",
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}.to_string()
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}
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}
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/// Enum of options for [STVOptions::exclusion]
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#[wasm_bindgen]
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#[derive(Clone, Copy)]
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#[derive(PartialEq)]
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pub enum ExclusionMethod {
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/// Transfer all ballot papers of an excluded candidate in one stage
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SingleStage,
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/// Transfer the ballot papers of an excluded candidate in descending order of accumulated transfer value
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ByValue,
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/// Transfer the ballot papers of an excluded candidate parcel by parcel in the order received
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ParcelsByOrder,
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}
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impl ExclusionMethod {
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/// Convert to CLI argument representation
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fn describe(self) -> String {
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match self {
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ExclusionMethod::SingleStage => "--exclusion single_stage",
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ExclusionMethod::ByValue => "--exclusion by_value",
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ExclusionMethod::ParcelsByOrder => "--exclusion parcels_by_order",
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}.to_string()
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}
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}
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/// An error during the STV count
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#[wasm_bindgen]
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#[derive(Debug)]
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pub enum STVError {
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/// User input is required
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RequireInput,
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/// Tie could not be resolved
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UnresolvedTie,
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}
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/// Distribute first preferences, and initialise other states such as the random number generator and tie-breaking rules
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pub fn count_init<'a, N: Number>(mut state: &mut CountState<'a, N>, opts: &'a STVOptions)
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where
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for<'r> &'r N: ops::Sub<&'r N, Output=N>,
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for<'r> &'r N: ops::Mul<&'r N, Output=N>,
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{
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// Initialise RNG
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for t in opts.ties.iter() {
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if let TieStrategy::Random(seed) = t {
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state.random = Some(SHARandom::new(seed));
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}
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}
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distribute_first_preferences(&mut state, opts);
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calculate_quota(&mut state, opts);
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elect_meeting_quota(&mut state, opts);
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init_tiebreaks(&mut state, opts);
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}
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/// Perform a single stage of the STV count
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pub fn count_one_stage<'a, N: Number>(mut state: &mut CountState<'a, N>, opts: &STVOptions) -> Result<bool, STVError>
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where
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for<'r> &'r N: ops::Sub<&'r N, Output=N>,
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for<'r> &'r N: ops::Mul<&'r N, Output=N>,
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for<'r> &'r N: ops::Div<&'r N, Output=N>,
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for<'r> &'r N: ops::Neg<Output=N>,
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{
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state.logger.entries.clear();
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state.step_all();
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// Finish count
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if finished_before_stage(&state) {
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return Ok(true);
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}
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// Continue exclusions
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if continue_exclusion(&mut state, &opts) {
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calculate_quota(&mut state, opts);
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elect_meeting_quota(&mut state, opts);
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update_tiebreaks(&mut state, opts);
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return Ok(false);
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}
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// Distribute surpluses
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if distribute_surpluses(&mut state, &opts)? {
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calculate_quota(&mut state, opts);
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elect_meeting_quota(&mut state, opts);
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update_tiebreaks(&mut state, opts);
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return Ok(false);
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}
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// Attempt bulk election
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if bulk_elect(&mut state, &opts)? {
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return Ok(false);
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}
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// Exclude lowest hopeful
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if exclude_hopefuls(&mut state, &opts)? {
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calculate_quota(&mut state, opts);
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elect_meeting_quota(&mut state, opts);
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update_tiebreaks(&mut state, opts);
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return Ok(false);
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}
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panic!("Count incomplete but unable to proceed");
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}
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/// See [next_preferences]
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struct NextPreferencesResult<'a, N> {
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candidates: HashMap<&'a Candidate, NextPreferencesEntry<'a, N>>,
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exhausted: NextPreferencesEntry<'a, N>,
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total_ballots: N,
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total_votes: N,
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}
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/// See [next_preferences]
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struct NextPreferencesEntry<'a, N> {
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//count_card: Option<&'a CountCard<'a, N>>,
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votes: Vec<Vote<'a, N>>,
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num_ballots: N,
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num_votes: N,
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}
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/// Count the given votes, grouping according to next available preference
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fn next_preferences<'a, N: Number>(state: &CountState<'a, N>, votes: Vec<Vote<'a, N>>) -> NextPreferencesResult<'a, N> {
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let mut result = NextPreferencesResult {
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candidates: HashMap::new(),
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exhausted: NextPreferencesEntry {
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votes: Vec::new(),
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num_ballots: N::new(),
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num_votes: N::new(),
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},
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total_ballots: N::new(),
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total_votes: N::new(),
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};
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for mut vote in votes.into_iter() {
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result.total_ballots += &vote.ballot.orig_value;
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result.total_votes += &vote.value;
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let mut next_candidate = None;
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for (i, preference) in vote.ballot.preferences.iter().enumerate().skip(vote.up_to_pref) {
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let candidate = &state.election.candidates[*preference];
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let count_card = state.candidates.get(candidate).unwrap();
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if let CandidateState::Hopeful | CandidateState::Guarded = count_card.state {
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next_candidate = Some(candidate);
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vote.up_to_pref = i + 1;
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break;
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}
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}
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// Have to structure like this to satisfy Rust's borrow checker
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if let Some(candidate) = next_candidate {
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if result.candidates.contains_key(candidate) {
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let entry = result.candidates.get_mut(candidate).unwrap();
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entry.num_ballots += &vote.ballot.orig_value;
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entry.num_votes += &vote.value;
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entry.votes.push(vote);
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} else {
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let entry = NextPreferencesEntry {
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num_ballots: vote.ballot.orig_value.clone(),
|
|
num_votes: vote.value.clone(),
|
|
votes: vec![vote],
|
|
};
|
|
result.candidates.insert(candidate, entry);
|
|
}
|
|
} else {
|
|
result.exhausted.num_ballots += &vote.ballot.orig_value;
|
|
result.exhausted.num_votes += &vote.value;
|
|
result.exhausted.votes.push(vote);
|
|
}
|
|
}
|
|
|
|
return result;
|
|
}
|
|
|
|
/// Distribute first preference votes
|
|
fn distribute_first_preferences<N: Number>(state: &mut CountState<N>, opts: &STVOptions)
|
|
where
|
|
for<'r> &'r N: ops::Sub<&'r N, Output=N>,
|
|
for<'r> &'r N: ops::Mul<&'r N, Output=N>,
|
|
{
|
|
match opts.surplus {
|
|
SurplusMethod::WIG | SurplusMethod::UIG | SurplusMethod::EG => {
|
|
gregory::distribute_first_preferences(state);
|
|
}
|
|
SurplusMethod::Meek => {
|
|
meek::distribute_first_preferences(state);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Calculate the quota, given the total vote, according to [STVOptions::quota]
|
|
fn total_to_quota<N: Number>(mut total: N, seats: usize, opts: &STVOptions) -> N {
|
|
match opts.quota {
|
|
QuotaType::Droop | QuotaType::DroopExact => {
|
|
total /= N::from(seats + 1);
|
|
}
|
|
QuotaType::Hare | QuotaType::HareExact => {
|
|
total /= N::from(seats);
|
|
}
|
|
}
|
|
|
|
if let Some(dps) = opts.round_quota {
|
|
match opts.quota {
|
|
QuotaType::Droop | QuotaType::Hare => {
|
|
// Increment to next available increment
|
|
let mut factor = N::from(10);
|
|
factor.pow_assign(dps as i32);
|
|
total *= &factor;
|
|
total.floor_mut(0);
|
|
total += N::one();
|
|
total /= factor;
|
|
}
|
|
QuotaType::DroopExact | QuotaType::HareExact => {
|
|
// Round up to next available increment if necessary
|
|
total.ceil_mut(dps);
|
|
}
|
|
}
|
|
}
|
|
|
|
return total;
|
|
}
|
|
|
|
/// Calculate the quota according to [STVOptions::quota]
|
|
fn calculate_quota<N: Number>(state: &mut CountState<N>, opts: &STVOptions) {
|
|
// Calculate quota
|
|
if state.quota.is_none() || opts.surplus == SurplusMethod::Meek {
|
|
let mut log = String::new();
|
|
|
|
// Calculate the total vote
|
|
let total_vote = state.candidates.values().fold(N::zero(), |acc, cc| { acc + &cc.votes });
|
|
log.push_str(format!("{:.dps$} usable votes, so the quota is ", total_vote, dps=opts.pp_decimals).as_str());
|
|
|
|
let quota = total_to_quota(total_vote, state.election.seats, opts);
|
|
|
|
log.push_str(format!("{:.dps$}.", quota, dps=opts.pp_decimals).as_str());
|
|
state.quota = Some(quota);
|
|
state.logger.log_literal(log);
|
|
}
|
|
|
|
if let QuotaMode::ERS97 = opts.quota_mode {
|
|
// ERS97 rules
|
|
|
|
// -------------------------
|
|
// Reduce quota if allowable
|
|
|
|
if state.num_elected == 0 {
|
|
let mut log = String::new();
|
|
|
|
// Calculate the total vote
|
|
let total_vote = state.candidates.values().fold(N::zero(), |acc, cc| { acc + &cc.votes });
|
|
log.push_str(format!("{:.dps$} usable votes, so the quota is reduced to ", total_vote, dps=opts.pp_decimals).as_str());
|
|
|
|
let quota = total_to_quota(total_vote, state.election.seats, opts);
|
|
|
|
if "a < state.quota.as_ref().unwrap() {
|
|
log.push_str(format!("{:.dps$}.", quota, dps=opts.pp_decimals).as_str());
|
|
state.quota = Some(quota);
|
|
state.logger.log_literal(log);
|
|
}
|
|
}
|
|
|
|
// ------------------------------------
|
|
// Calculate vote required for election
|
|
|
|
if state.num_elected < state.election.seats {
|
|
let mut log = String::new();
|
|
|
|
// Calculate total active vote
|
|
let total_active_vote = state.candidates.values().fold(N::zero(), |acc, cc| {
|
|
match cc.state {
|
|
CandidateState::Elected => { if &cc.votes > state.quota.as_ref().unwrap() { acc + &cc.votes - state.quota.as_ref().unwrap() } else { acc } }
|
|
_ => { acc + &cc.votes }
|
|
}
|
|
});
|
|
log.push_str(format!("Total active vote is {:.dps$}, so the vote required for election is ", total_active_vote, dps=opts.pp_decimals).as_str());
|
|
|
|
let vote_req = total_to_quota(total_active_vote, state.election.seats - state.num_elected, opts);
|
|
|
|
if &vote_req < state.quota.as_ref().unwrap() {
|
|
// VRE is less than the quota
|
|
if let Some(v) = &state.vote_required_election {
|
|
if &vote_req != v {
|
|
log.push_str(format!("{:.dps$}.", vote_req, dps=opts.pp_decimals).as_str());
|
|
state.vote_required_election = Some(vote_req);
|
|
state.logger.log_literal(log);
|
|
}
|
|
} else {
|
|
log.push_str(format!("{:.dps$}.", vote_req, dps=opts.pp_decimals).as_str());
|
|
state.vote_required_election = Some(vote_req);
|
|
state.logger.log_literal(log);
|
|
}
|
|
} else {
|
|
// VRE is not less than the quota, so use the quota
|
|
state.vote_required_election = state.quota.clone();
|
|
}
|
|
}
|
|
} else {
|
|
// No ERS97 rules
|
|
if state.vote_required_election.is_none() || opts.surplus == SurplusMethod::Meek {
|
|
state.vote_required_election = state.quota.clone();
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Determine if the given candidate meets the quota, according to [STVOptions::quota_criterion]
|
|
fn meets_quota<N: Number>(quota: &N, count_card: &CountCard<N>, opts: &STVOptions) -> bool {
|
|
match opts.quota_criterion {
|
|
QuotaCriterion::GreaterOrEqual => {
|
|
return count_card.votes >= *quota;
|
|
}
|
|
QuotaCriterion::Greater => {
|
|
return count_card.votes > *quota;
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Declare elected all candidates meeting the quota
|
|
fn elect_meeting_quota<N: Number>(state: &mut CountState<N>, opts: &STVOptions) {
|
|
let vote_req = state.vote_required_election.as_ref().unwrap(); // Have to do this or else the borrow checker gets confused
|
|
|
|
let mut cands_meeting_quota: Vec<&Candidate> = state.election.candidates.iter()
|
|
.filter(|c| { let cc = state.candidates.get(c).unwrap(); cc.state == CandidateState::Hopeful && meets_quota(vote_req, cc, opts) })
|
|
.collect();
|
|
|
|
if !cands_meeting_quota.is_empty() {
|
|
// Sort by votes
|
|
cands_meeting_quota.sort_unstable_by(|a, b| state.candidates.get(a).unwrap().votes.cmp(&state.candidates.get(b).unwrap().votes));
|
|
|
|
// Declare elected in descending order of votes
|
|
for candidate in cands_meeting_quota.into_iter().rev() {
|
|
let count_card = state.candidates.get_mut(candidate).unwrap();
|
|
count_card.state = CandidateState::Elected;
|
|
state.num_elected += 1;
|
|
count_card.order_elected = state.num_elected as isize;
|
|
state.logger.log_smart(
|
|
"{} meets the quota and is elected.",
|
|
"{} meet the quota and are elected.",
|
|
vec![&candidate.name]
|
|
);
|
|
|
|
if opts.quota_mode == QuotaMode::ERS97 {
|
|
// Vote required for election may have changed
|
|
calculate_quota(state, opts);
|
|
}
|
|
}
|
|
|
|
if opts.quota_mode == QuotaMode::ERS97 {
|
|
// Repeat in case vote required for election has changed
|
|
//calculate_quota(state, opts);
|
|
elect_meeting_quota(state, opts);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Determine whether the transfer of all surpluses can be deferred
|
|
///
|
|
/// The value of [STVOptions::defer_surpluses] is not taken into account and must be handled by the caller
|
|
fn can_defer_surpluses<N: Number>(state: &CountState<N>, opts: &STVOptions, total_surpluses: &N) -> bool
|
|
where
|
|
for<'r> &'r N: ops::Sub<&'r N, Output=N>
|
|
{
|
|
// Do not defer if this could change the last 2 candidates
|
|
let mut hopefuls: Vec<(&&Candidate, &CountCard<N>)> = state.candidates.iter()
|
|
.filter(|(_, cc)| cc.state == CandidateState::Hopeful || cc.state == CandidateState::Guarded)
|
|
.collect();
|
|
hopefuls.sort_unstable_by(|(_, cc1), (_, cc2)| cc1.votes.cmp(&cc2.votes));
|
|
if total_surpluses > &(&hopefuls[1].1.votes - &hopefuls[0].1.votes) {
|
|
return false;
|
|
}
|
|
|
|
// Do not defer if this could affect a bulk exclusion
|
|
if opts.bulk_exclude {
|
|
let to_exclude = hopefuls_to_bulk_exclude(state, opts);
|
|
let num_to_exclude = to_exclude.len();
|
|
if num_to_exclude > 0 {
|
|
let total_excluded = to_exclude.into_iter()
|
|
.fold(N::new(), |acc, c| acc + &state.candidates.get(c).unwrap().votes);
|
|
if total_surpluses > &(&hopefuls[num_to_exclude + 1].1.votes - &total_excluded) {
|
|
return false;
|
|
}
|
|
}
|
|
}
|
|
return true;
|
|
}
|
|
|
|
/// Distribute surpluses according to [STVOptions::surplus]
|
|
fn distribute_surpluses<N: Number>(state: &mut CountState<N>, opts: &STVOptions) -> Result<bool, STVError>
|
|
where
|
|
for<'r> &'r N: ops::Sub<&'r N, Output=N>,
|
|
for<'r> &'r N: ops::Mul<&'r N, Output=N>,
|
|
for<'r> &'r N: ops::Div<&'r N, Output=N>,
|
|
for<'r> &'r N: ops::Neg<Output=N>,
|
|
{
|
|
match opts.surplus {
|
|
SurplusMethod::WIG | SurplusMethod::UIG | SurplusMethod::EG => {
|
|
return gregory::distribute_surpluses(state, opts);
|
|
}
|
|
SurplusMethod::Meek => {
|
|
return meek::distribute_surpluses(state, opts);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Declare all continuing candidates elected, if the number equals the number of remaining vacancies
|
|
fn bulk_elect<N: Number>(state: &mut CountState<N>, opts: &STVOptions) -> Result<bool, STVError> {
|
|
if state.election.candidates.len() - state.num_excluded <= state.election.seats {
|
|
state.kind = None;
|
|
state.title = "Bulk election".to_string();
|
|
|
|
// Bulk elect all remaining candidates
|
|
let mut hopefuls: Vec<&Candidate> = state.election.candidates.iter()
|
|
.filter(|c| state.candidates.get(c).unwrap().state == CandidateState::Hopeful)
|
|
.collect();
|
|
|
|
while !hopefuls.is_empty() {
|
|
let max_votes = hopefuls.iter()
|
|
.max_by(|a, b| state.candidates.get(**a).unwrap().votes.cmp(&state.candidates.get(**b).unwrap().votes))
|
|
.unwrap();
|
|
let max_votes = &state.candidates.get(max_votes).unwrap().votes;
|
|
let max_hopefuls: Vec<&Candidate> = hopefuls.iter()
|
|
.filter(|c| &state.candidates.get(**c).unwrap().votes == max_votes)
|
|
.map(|c| *c)
|
|
.collect();
|
|
|
|
let candidate;
|
|
if max_hopefuls.len() > 1 {
|
|
// Handle ties
|
|
candidate = choose_highest(state, opts, max_hopefuls)?;
|
|
} else {
|
|
candidate = max_hopefuls[0];
|
|
}
|
|
|
|
let count_card = state.candidates.get_mut(candidate).unwrap();
|
|
count_card.state = CandidateState::Elected;
|
|
state.num_elected += 1;
|
|
count_card.order_elected = state.num_elected as isize;
|
|
|
|
state.logger.log_smart(
|
|
"{} is elected to fill the remaining vacancy.",
|
|
"{} are elected to fill the remaining vacancies.",
|
|
vec![&candidate.name]
|
|
);
|
|
|
|
hopefuls.remove(hopefuls.iter().position(|c| *c == candidate).unwrap());
|
|
}
|
|
|
|
return Ok(true);
|
|
}
|
|
return Ok(false);
|
|
}
|
|
|
|
/// Determine which continuing candidates could be excluded in a bulk exclusion
|
|
///
|
|
/// The value of [STVOptions::bulk_exclude] is not taken into account and must be handled by the caller
|
|
fn hopefuls_to_bulk_exclude<'a, N: Number>(state: &CountState<'a, N>, _opts: &STVOptions) -> Vec<&'a Candidate> {
|
|
let mut excluded_candidates = Vec::new();
|
|
|
|
let mut hopefuls: Vec<(&&Candidate, &CountCard<N>)> = state.candidates.iter()
|
|
.filter(|(_, cc)| cc.state == CandidateState::Hopeful)
|
|
.collect();
|
|
|
|
// Sort by votes
|
|
// NB: Unnecessary to handle ties, as ties will be rejected at "Do not exclude if this could change the order of exclusion"
|
|
hopefuls.sort_unstable_by(|a, b| a.1.votes.cmp(&b.1.votes));
|
|
|
|
let total_surpluses = state.candidates.iter()
|
|
.filter(|(_, cc)| &cc.votes > state.quota.as_ref().unwrap())
|
|
.fold(N::new(), |agg, (_, cc)| agg + &cc.votes - state.quota.as_ref().unwrap());
|
|
|
|
// Attempt to exclude as many candidates as possible
|
|
for i in 0..hopefuls.len() {
|
|
let try_exclude = &hopefuls[0..hopefuls.len()-i];
|
|
|
|
// Do not exclude if this leaves insufficient candidates
|
|
if state.num_elected + hopefuls.len() - try_exclude.len() < state.election.seats {
|
|
continue;
|
|
}
|
|
|
|
// Do not exclude if this could change the order of exclusion
|
|
let total_votes = try_exclude.into_iter().fold(N::new(), |agg, (_, cc)| agg + &cc.votes);
|
|
if i != 0 && total_votes + &total_surpluses >= hopefuls[hopefuls.len()-i].1.votes {
|
|
continue;
|
|
}
|
|
|
|
for (c, _) in try_exclude.into_iter() {
|
|
excluded_candidates.push(**c);
|
|
}
|
|
break;
|
|
}
|
|
|
|
return excluded_candidates;
|
|
}
|
|
|
|
/// Exclude the lowest-ranked hopeful candidate(s)
|
|
fn exclude_hopefuls<'a, N: Number>(state: &mut CountState<'a, N>, opts: &STVOptions) -> Result<bool, STVError>
|
|
where
|
|
for<'r> &'r N: ops::Sub<&'r N, Output=N>,
|
|
for<'r> &'r N: ops::Mul<&'r N, Output=N>,
|
|
for<'r> &'r N: ops::Div<&'r N, Output=N>,
|
|
{
|
|
let mut excluded_candidates: Vec<&Candidate> = Vec::new();
|
|
|
|
// Attempt a bulk exclusion
|
|
if opts.bulk_exclude {
|
|
excluded_candidates = hopefuls_to_bulk_exclude(state, opts);
|
|
}
|
|
|
|
// Exclude lowest ranked candidate
|
|
if excluded_candidates.is_empty() {
|
|
let mut hopefuls: Vec<(&Candidate, &CountCard<N>)> = state.election.candidates.iter() // Present in order in case of tie
|
|
.map(|c| (c, state.candidates.get(c).unwrap()))
|
|
.filter(|(_, cc)| cc.state == CandidateState::Hopeful)
|
|
.collect();
|
|
|
|
// Sort by votes
|
|
hopefuls.sort_by(|a, b| a.1.votes.cmp(&b.1.votes));
|
|
|
|
// Handle ties
|
|
if hopefuls.len() > 1 && hopefuls[0].1.votes == hopefuls[1].1.votes {
|
|
let min_votes = &hopefuls[0].1.votes;
|
|
let hopefuls = hopefuls.into_iter().filter_map(|(c, cc)| if &cc.votes == min_votes { Some(c) } else { None }).collect();
|
|
excluded_candidates = vec![choose_lowest(state, opts, hopefuls)?];
|
|
} else {
|
|
excluded_candidates = vec![&hopefuls[0].0];
|
|
}
|
|
}
|
|
|
|
let mut names: Vec<&str> = excluded_candidates.iter().map(|c| c.name.as_str()).collect();
|
|
names.sort();
|
|
state.kind = Some("Exclusion of");
|
|
state.title = names.join(", ");
|
|
state.logger.log_smart(
|
|
"No surpluses to distribute, so {} is excluded.",
|
|
"No surpluses to distribute, so {} are excluded.",
|
|
names
|
|
);
|
|
|
|
exclude_candidates(state, opts, excluded_candidates);
|
|
|
|
return Ok(true);
|
|
}
|
|
|
|
/// Continue the exclusion of a candidate who is being excluded
|
|
fn continue_exclusion<'a, N: Number>(state: &mut CountState<'a, N>, opts: &STVOptions) -> bool
|
|
where
|
|
for<'r> &'r N: ops::Sub<&'r N, Output=N>,
|
|
for<'r> &'r N: ops::Mul<&'r N, Output=N>,
|
|
for<'r> &'r N: ops::Div<&'r N, Output=N>,
|
|
{
|
|
// Cannot filter by raw vote count, as candidates may have 0.00 votes but still have recorded ballot papers
|
|
let mut excluded_with_votes: Vec<(&&Candidate, &CountCard<N>)> = state.candidates.iter()
|
|
.filter(|(_, cc)| cc.state == CandidateState::Excluded && cc.parcels.iter().any(|p| !p.is_empty()))
|
|
.collect();
|
|
|
|
if !excluded_with_votes.is_empty() {
|
|
excluded_with_votes.sort_unstable_by(|a, b| a.1.order_elected.cmp(&b.1.order_elected));
|
|
|
|
let order_excluded = excluded_with_votes[0].1.order_elected;
|
|
let excluded_candidates: Vec<&Candidate> = excluded_with_votes.into_iter()
|
|
.filter(|(_, cc)| cc.order_elected == order_excluded)
|
|
.map(|(c, _)| *c)
|
|
.collect();
|
|
|
|
let mut names: Vec<&str> = excluded_candidates.iter().map(|c| c.name.as_str()).collect();
|
|
names.sort();
|
|
state.kind = Some("Exclusion of");
|
|
state.title = names.join(", ");
|
|
state.logger.log_smart(
|
|
"Continuing exclusion of {}.",
|
|
"Continuing exclusion of {}.",
|
|
names
|
|
);
|
|
|
|
exclude_candidates(state, opts, excluded_candidates);
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
/// Perform one stage of a candidate exclusion, according to [STVOptions::exclusion]
|
|
fn exclude_candidates<'a, N: Number>(state: &mut CountState<'a, N>, opts: &STVOptions, excluded_candidates: Vec<&'a Candidate>)
|
|
where
|
|
for<'r> &'r N: ops::Sub<&'r N, Output=N>,
|
|
for<'r> &'r N: ops::Mul<&'r N, Output=N>,
|
|
for<'r> &'r N: ops::Div<&'r N, Output=N>,
|
|
{
|
|
match opts.surplus {
|
|
SurplusMethod::WIG | SurplusMethod::UIG | SurplusMethod::EG => {
|
|
gregory::exclude_candidates(state, opts, excluded_candidates);
|
|
}
|
|
SurplusMethod::Meek => {
|
|
meek::exclude_candidates(state, opts, excluded_candidates);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// Determine if the count is complete because the number of elected candidates equals the number of vacancies
|
|
fn finished_before_stage<N: Number>(state: &CountState<N>) -> bool {
|
|
if state.num_elected >= state.election.seats {
|
|
return true;
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// Break a tie between the given candidates according to [STVOptions::ties], selecting the highest candidate
|
|
///
|
|
/// The given candidates are assumed to be tied in this round
|
|
fn choose_highest<'c, N: Number>(state: &mut CountState<N>, opts: &STVOptions, candidates: Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
|
|
for strategy in opts.ties.iter() {
|
|
match strategy.choose_highest(state, &candidates) {
|
|
Ok(c) => {
|
|
return Ok(c);
|
|
}
|
|
Err(e) => {
|
|
if let STVError::UnresolvedTie = e {
|
|
continue;
|
|
} else {
|
|
return Err(e);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
panic!("Unable to resolve tie");
|
|
}
|
|
|
|
/// Break a tie between the given candidates according to [STVOptions::ties], selecting the lowest candidate
|
|
///
|
|
/// The given candidates are assumed to be tied in this round
|
|
fn choose_lowest<'c, N: Number>(state: &mut CountState<N>, opts: &STVOptions, candidates: Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
|
|
for strategy in opts.ties.iter() {
|
|
match strategy.choose_lowest(state, &candidates) {
|
|
Ok(c) => {
|
|
return Ok(c);
|
|
}
|
|
Err(e) => {
|
|
if let STVError::UnresolvedTie = e {
|
|
continue;
|
|
} else {
|
|
return Err(e);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
panic!("Unable to resolve tie");
|
|
}
|
|
|
|
/// If required, initialise the state of the forwards or backwards tie-breaking strategies, according to [STVOptions::ties]
|
|
fn init_tiebreaks<N: Number>(state: &mut CountState<N>, opts: &STVOptions) {
|
|
if !opts.ties.iter().any(|t| t == &TieStrategy::Forwards) && !opts.ties.iter().any(|t| t == &TieStrategy::Backwards) {
|
|
return;
|
|
}
|
|
|
|
// Sort candidates in this stage by votes, grouping by ties
|
|
let mut sorted_candidates: Vec<(&&Candidate, &CountCard<N>)> = state.candidates.iter().collect();
|
|
sorted_candidates.sort_unstable_by(|a, b| a.1.votes.cmp(&b.1.votes));
|
|
let sorted_candidates: Vec<Vec<(&&Candidate, &CountCard<N>)>> = sorted_candidates.into_iter()
|
|
.group_by(|(_, cc)| &cc.votes)
|
|
.into_iter()
|
|
.map(|(_, candidates)| candidates.collect())
|
|
.collect();
|
|
|
|
// Update forwards tie-breaking order
|
|
if opts.ties.iter().any(|t| t == &TieStrategy::Forwards) {
|
|
let mut hm: HashMap<&Candidate, usize> = HashMap::new();
|
|
for (i, group) in sorted_candidates.iter().enumerate() {
|
|
for (candidate, _) in group.iter() {
|
|
hm.insert(candidate, i);
|
|
}
|
|
}
|
|
state.forwards_tiebreak = Some(hm);
|
|
}
|
|
|
|
// Update backwards tie-breaking order
|
|
if opts.ties.iter().any(|t| t == &TieStrategy::Backwards) {
|
|
let mut hm: HashMap<&Candidate, usize> = HashMap::new();
|
|
for (i, group) in sorted_candidates.iter().enumerate() {
|
|
for (candidate, _) in group.iter() {
|
|
hm.insert(candidate, i);
|
|
}
|
|
}
|
|
state.backwards_tiebreak = Some(hm);
|
|
}
|
|
}
|
|
|
|
/// If required, update the state of the forwards or backwards tie-breaking strategies, according to [STVOptions::ties]
|
|
fn update_tiebreaks<N: Number>(state: &mut CountState<N>, _opts: &STVOptions) {
|
|
if let None = state.forwards_tiebreak {
|
|
if let None = state.backwards_tiebreak {
|
|
return;
|
|
}
|
|
}
|
|
|
|
// Sort candidates in this stage by votes, grouping by ties
|
|
let mut sorted_candidates: Vec<(&&Candidate, &CountCard<N>)> = state.candidates.iter().collect();
|
|
sorted_candidates.sort_unstable_by(|a, b| a.1.votes.cmp(&b.1.votes));
|
|
let sorted_candidates: Vec<Vec<&Candidate>> = sorted_candidates.into_iter()
|
|
.group_by(|(_, cc)| &cc.votes)
|
|
.into_iter()
|
|
.map(|(_, candidates)| candidates.map(|(c, _)| *c).collect())
|
|
.collect();
|
|
|
|
// Update forwards tie-breaking order
|
|
if let Some(hm) = state.forwards_tiebreak.as_mut() {
|
|
// TODO: Check if already completely sorted
|
|
let mut sorted_last_round: Vec<(&&Candidate, &usize)> = hm.iter().collect();
|
|
sorted_last_round.sort_unstable_by(|a, b| a.1.cmp(b.1));
|
|
let sorted_last_round: Vec<Vec<&Candidate>> = sorted_last_round.into_iter()
|
|
.group_by(|(_, v)| **v)
|
|
.into_iter()
|
|
.map(|(_, group)| group.map(|(c, _)| *c).collect())
|
|
.collect();
|
|
|
|
let mut i: usize = 0;
|
|
for mut group in sorted_last_round.into_iter() {
|
|
if group.len() == 1 {
|
|
hm.insert(group[0], i);
|
|
i += 1;
|
|
continue;
|
|
} else {
|
|
// Tied in last round - refer to this round
|
|
group.sort_unstable_by(|a, b|
|
|
sorted_candidates.iter().position(|x| x.contains(a)).unwrap()
|
|
.cmp(&sorted_candidates.iter().position(|x| x.contains(b)).unwrap())
|
|
);
|
|
let tied_last_round = group.into_iter()
|
|
.group_by(|c| sorted_candidates.iter().position(|x| x.contains(c)).unwrap());
|
|
|
|
for (_, group2) in tied_last_round.into_iter() {
|
|
for candidate in group2 {
|
|
hm.insert(candidate, i);
|
|
}
|
|
i += 1;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Update backwards tie-breaking order
|
|
if let Some(hm) = state.backwards_tiebreak.as_mut() {
|
|
let hm_orig = hm.clone();
|
|
let mut i: usize = 0;
|
|
for group in sorted_candidates.iter() {
|
|
if group.len() == 1 {
|
|
hm.insert(group[0], i);
|
|
i += 1;
|
|
continue;
|
|
} else {
|
|
// Tied in this round - refer to last round
|
|
let mut tied_this_round: Vec<&Candidate> = group.into_iter().map(|c| *c).collect();
|
|
tied_this_round.sort_unstable_by(|a, b| hm_orig.get(a).unwrap().cmp(hm_orig.get(b).unwrap()));
|
|
let tied_this_round = tied_this_round.into_iter()
|
|
.group_by(|c| hm_orig.get(c).unwrap());
|
|
|
|
for (_, group2) in tied_this_round.into_iter() {
|
|
for candidate in group2 {
|
|
hm.insert(candidate, i);
|
|
}
|
|
i += 1;
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|