251 lines
7.4 KiB
Rust
251 lines
7.4 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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use super::{STVOptions, SumSurplusTransfersMode};
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use crate::election::{Candidate, CountState};
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use crate::numbers::Number;
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use std::collections::HashMap;
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/// Table describing vote transfers during a surplus distribution or exclusion
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pub struct TransferTable<'e, N: Number> {
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/// Columns in the table
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pub columns: Vec<TransferTableColumn<'e, N>>,
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}
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impl<'e, N: Number> TransferTable<'e, N> {
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/// Return a new [TransferTable]
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pub fn new() -> Self {
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TransferTable {
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columns: Vec::new(),
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}
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}
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/// Record the specified transfer
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pub fn add_transfers(&mut self, value_fraction: &N, candidate: &'e Candidate, ballots: &N) {
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for col in self.columns.iter_mut() {
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if &col.value_fraction == value_fraction {
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col.add_transfers(candidate, ballots);
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return;
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}
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}
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let mut col = TransferTableColumn {
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value_fraction: value_fraction.clone(),
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cells: HashMap::new(),
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exhausted: TransferTableCell { ballots: N::new() },
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};
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col.add_transfers(candidate, ballots);
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self.columns.push(col);
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}
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/// Record the specified exhaustion
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pub fn add_exhausted(&mut self, value_fraction: &N, ballots: &N) {
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for col in self.columns.iter_mut() {
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if &col.value_fraction == value_fraction {
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col.exhausted.ballots += ballots;
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return;
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}
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}
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let col = TransferTableColumn {
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value_fraction: value_fraction.clone(),
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cells: HashMap::new(),
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exhausted: TransferTableCell { ballots: ballots.clone() },
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};
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self.columns.push(col);
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}
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/// Apply the transfers described in the table to the count sheet
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///
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/// Credit continuing candidates and exhausted pile with the appropriate number of ballot papers and votes.
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pub fn apply_to(&self, state: &mut CountState<N>, opts: &STVOptions, surplus: Option<&N>, surplus_numer: &Option<N>, surplus_denom: &Option<N>) -> N {
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// Use weighted rules if exclusion or WIGM
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let is_weighted = surplus.is_none() || opts.surplus.is_weighted();
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let mut checksum = N::new();
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// Credit transferred votes
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for (candidate, count_card) in state.candidates.iter_mut() {
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let mut votes_transferred = N::new();
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let mut ballots_transferred = N::new();
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// If exclusion, or surplus at present value, or SumSurplusTransfersMode::ByValue
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if surplus_numer.is_none() || opts.sum_surplus_transfers == SumSurplusTransfersMode::ByValue {
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// Calculate transfer across all votes in this parcel
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for column in self.columns.iter() {
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if let Some(cell) = column.cells.get(*candidate) {
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if is_weighted {
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votes_transferred += cell.ballots.clone() * &column.value_fraction;
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}
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ballots_transferred += &cell.ballots;
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}
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}
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if !is_weighted {
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votes_transferred = ballots_transferred.clone();
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}
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// If surplus, multiply by surplus fraction
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if let Some(n) = &surplus_numer {
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votes_transferred *= n;
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}
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if let Some(n) = &surplus_denom {
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votes_transferred /= n;
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}
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} else if opts.sum_surplus_transfers == SumSurplusTransfersMode::PerBallot {
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// Sum transfer per each individual ballot
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for column in self.columns.iter() {
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if let Some(cell) = column.cells.get(*candidate) {
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ballots_transferred += &cell.ballots;
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let mut new_value_fraction;
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if is_weighted {
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new_value_fraction = column.value_fraction.clone();
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// If surplus, multiply by surplus fraction
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if let Some(n) = &surplus_numer {
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new_value_fraction *= n;
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}
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if let Some(n) = &surplus_denom {
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new_value_fraction /= n;
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}
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// Round if required
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if let Some(dps) = opts.round_values {
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new_value_fraction.floor_mut(dps);
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}
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} else {
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if let Some(n) = &surplus_numer {
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new_value_fraction = n.clone();
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} else {
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// Transferred at original value
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new_value_fraction = column.value_fraction.clone();
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}
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if let Some(n) = &surplus_denom {
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new_value_fraction /= n;
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}
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// Round if required
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if let Some(dps) = opts.round_values {
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new_value_fraction.floor_mut(dps);
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}
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}
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votes_transferred += cell.ballots.clone() * new_value_fraction;
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}
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}
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} else {
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unreachable!();
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}
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// Round if required
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if let Some(dps) = opts.round_votes {
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votes_transferred.floor_mut(dps);
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}
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count_card.transfer(&votes_transferred);
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count_card.ballot_transfers += ballots_transferred;
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checksum += votes_transferred;
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}
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// Credit exhausted votes
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// If exclusion or not --transferable-only
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if surplus.is_none() || !opts.transferable_only {
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// Standard rules
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let mut votes_transferred = N::new();
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let mut ballots_transferred = N::new();
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for column in self.columns.iter() {
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if is_weighted {
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votes_transferred += column.exhausted.ballots.clone() * &column.value_fraction;
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}
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ballots_transferred += &column.exhausted.ballots;
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}
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if !is_weighted {
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votes_transferred = ballots_transferred.clone();
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}
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// If surplus, multiply by surplus fraction
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if let Some(n) = &surplus_numer {
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votes_transferred *= n;
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}
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if let Some(n) = &surplus_denom {
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votes_transferred /= n;
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}
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// Round if required
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if let Some(dps) = opts.round_votes {
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votes_transferred.floor_mut(dps);
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}
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state.exhausted.transfer(&votes_transferred);
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state.exhausted.ballot_transfers += ballots_transferred;
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checksum += votes_transferred;
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} else {
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// Credit only nontransferable difference
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if surplus_numer.is_none() {
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// TODO: Is there a purer way of calculating this?
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let difference = surplus.unwrap().clone() - &checksum;
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state.exhausted.transfer(&difference);
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checksum += difference;
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for column in self.columns.iter() {
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state.exhausted.ballot_transfers += &column.exhausted.ballots;
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}
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} else {
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// No ballots exhaust
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}
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}
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return checksum;
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}
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}
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/// Column in a [TransferTable]
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pub struct TransferTableColumn<'e, N: Number> {
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/// Value fraction of ballots counted in this column
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pub value_fraction: N,
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/// Cells in this column
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pub cells: HashMap<&'e Candidate, TransferTableCell<N>>,
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/// Exhausted cell
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pub exhausted: TransferTableCell<N>,
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}
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impl<'e, N: Number> TransferTableColumn<'e, N> {
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/// Record the specified transfer
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pub fn add_transfers(&mut self, candidate: &'e Candidate, ballots: &N) {
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if let Some(cell) = self.cells.get_mut(candidate) {
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cell.ballots += ballots;
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} else {
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let cell = TransferTableCell {
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ballots: ballots.clone(),
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};
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self.cells.insert(candidate, cell);
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}
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}
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}
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/// Cell in a [TransferTable], representing transfers to one candidate at a particular value
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pub struct TransferTableCell<N: Number> {
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/// Ballots transferred to this candidate
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pub ballots: N,
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}
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