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with Ada.Strings.Fixed;
with Ada.Strings.Unbounded;
with Ada.Text_IO;
use Ada.Text_IO;
with Rationals;
-- This source is licensed under Creative Commons CC0 v1.0.
--
-- To read the full text, see license.txt in the main directory of this repository
-- or go to https://creativecommons.org/publicdomain/zero/1.0/legalcode.txt
--
-- For a human readable summary, go to https://creativecommons.org/publicdomain/zero/1.0/
package body Election is
package SU renames Ada.Strings.Unbounded;
-- Candidate, preference data, and other information
-- that's actively used by the main STV algorithm.
Pref_Data : Bundle_Containers.Bundle_Map;
Cand_Data : Candidates.Containers.Candidate_Map;
Entries : Entry_Vectors.Vector;
Exhausted : Extra_Data;
Fractional : Extra_Data;
Transfers : Transfer_Vectors.Vector;
-- Logging settings.
Out_Dir : SU.Unbounded_String;
Next_Log_Num : Positive;
Main_Log : File_Type;
-- Static info about the election.
-- (Although Vacancies gets modified as seats are won.)
Seats : Natural;
Vacancies : Natural;
Total_Papers : Natural;
Quota : Natural;
-- Administrative details of the program.
Verbose : Boolean;
Work_To_Do : Boolean := False;
function Droop_Quota
(Votes : in Natural;
Seats : in Natural)
return Natural is
begin
return Votes / (Seats + 1) + 1;
end Droop_Quota;
-- Extracts and sets up relevant entry metadata from the preference bundle map.
procedure Read_Entries
is
Votes, Papers : Integer;
This : Entry_Data;
begin
Entries := Entry_Vectors.Empty_Vector;
for B in Pref_Data.Iterate loop
Given_Bundles.Count_Both
(Bundle_Containers.Bundle_Maps.Element (B).First_Element, Votes, Papers);
This :=
(ID => Bundle_Containers.Bundle_Maps.Key (B),
Vote_Change => Votes,
Total_Votes => Votes,
Paper_Change => Papers,
Total_Papers => Papers,
Status => Running,
Changed => False,
Order_Elected => 0);
Entries.Append (This);
end loop;
end Read_Entries;
-- This must be called before an election is run.
procedure Setup
(Candidate_Data : in Candidates.Containers.Candidate_Map;
Preference_File : in String;
Output_Dir, Main_Logfile : in String;
Number_To_Elect : in Natural;
Is_Verbose : in Boolean := False) is
begin
Verbose := Is_Verbose;
if Verbose then
Put_Line (Standard_Error, "Reading preference data...");
end if;
Bundle_Containers.Read_Bundles (Preference_File, Pref_Data);
if Verbose then
Put_Line (Standard_Error, "Done." & ASCII.LF);
Put_Line (Standard_Error, "Setting up election...");
end if;
Cand_Data := Candidate_Data;
Read_Entries;
Exhausted := (others => 0);
Fractional := (others => 0);
Transfers := Transfer_Vectors.Empty_Vector;
Out_Dir := SU.To_Unbounded_String (Output_Dir);
Next_Log_Num := 1;
Open (Main_Log, Append_File, Output_Dir & "/" & Main_Logfile);
Seats := Number_To_Elect;
Vacancies := Number_To_Elect;
Total_Papers := 0;
for E of Entries loop
Total_Papers := Total_Papers + E.Total_Papers;
end loop;
Quota := Droop_Quota (Total_Papers, Seats);
Work_To_Do := True;
if Verbose then
Put_Line (Standard_Error, "Done." & ASCII.LF);
end if;
end Setup;
-- This is used because the 'Image attribute
-- puts unwanted padding either side of numbers.
function Int_Image
(Number : in Integer)
return String
is
use Ada.Strings;
use Ada.Strings.Fixed;
Result : String :=
Trim (Integer'Image (Number), Both);
begin
return Result;
end Int_Image;
-- Outputs a new numbered csv logfile of the current status of the election.
-- Automatically increments the logfile number afterwards.
procedure Write_Log
is
Header : String :=
"Seats,Vacancies,Total Papers,Quota," &
Candidates.Candidate_Header &
",Papers,Change,Votes,Transfer,Status,Changed,Order Elected";
Logname : String :=
SU.To_String (Out_Dir) & "/" & Int_Image (Next_Log_Num) & ".csv";
Change_Str, Order_Str : SU.Unbounded_String;
Logfile : File_Type;
begin
Create (Logfile, Out_File, Logname);
Put_Line (Logfile, Header);
for E of Entries loop
if E.Changed then
Change_Str := SU.To_Unbounded_String ("True");
else
Change_Str := SU.To_Unbounded_String (0);
end if;
if E.Order_Elected > 0 then
Order_Str := SU.To_Unbounded_String (Int_Image (E.Order_Elected));
else
Order_Str := SU.To_Unbounded_String (0);
end if;
Put_Line (Logfile,
Int_Image (Seats) & "," &
Int_Image (Vacancies) & "," &
Int_Image (Total_Papers) & "," &
Int_Image (Quota) & "," &
Candidates.To_String (Cand_Data.Element (E.ID)) & "," &
Int_Image (E.Total_Papers) & "," &
Int_Image (E.Paper_Change) & "," &
Int_Image (E.Total_Votes) & "," &
Int_Image (E.Vote_Change) & "," &
Candidate_Status'Image (E.Status) & "," &
SU.To_String (Change_Str) & "," &
SU.To_String (Order_Str));
end loop;
-- I don't really like how it's not obvious by looking at this
-- whether the correct number of commas is being used.
Put_Line (Logfile,
",,,,,,Fractional Loss,,," &
Int_Image (Fractional.Total_Papers) & "," &
Int_Image (Fractional.Paper_Change) & "," &
",,,,");
Put_Line (Logfile,
",,,,,,Exhausted,,," &
Int_Image (Exhausted.Total_Papers) & "," &
Int_Image (Exhausted.Paper_Change) & "," &
",,,,");
Close (Logfile);
Next_Log_Num := Next_Log_Num + 1;
end Write_Log;
type Entry_Position is record
Index : Positive;
Total_Votes : Natural;
end record;
package Position_Vectors is new Ada.Containers.Vectors
(Index_Type => Positive,
Element_Type => Entry_Position);
-- Ordering is stable with respect to the original candidate
-- order in the event of multiple entries have equal votes.
function "<"
(Left, Right : in Entry_Position)
return Boolean is
begin
if Left.Total_Votes = Right.Total_Votes then
return Left.Index < Right.Index;
else
return Left.Total_Votes < Right.Total_Votes;
end if;
end "<";
package Position_Sorting is new Position_Vectors.Generic_Sorting;
-- The above types and this function are used to be able to sort
-- still running entries by how many votes they have without
-- messing up their original order, since the order should be
-- consistent between numbered logfiles.
function Get_Running_Entry_Positions
return Position_Vectors.Vector
is
Result : Position_Vectors.Vector := Position_Vectors.Empty_Vector;
begin
for E in Entries.Iterate loop
if Entry_Vectors.Element (E).Status = Running then
Result.Append
((Index => Entry_Vectors.To_Index (E),
Total_Votes => Entry_Vectors.Element (E).Total_Votes));
end if;
end loop;
return Result;
end Get_Running_Entry_Positions;
-- Only used by the Transfer_Votes function.
function Get_Not_Running_IDs
return Candidates.Containers.CandidateID_Sets.Set
is
Result : Candidates.Containers.CandidateID_Sets.Set :=
Candidates.Containers.CandidateID_Sets.Empty_Set;
begin
for E of Entries loop
if E.Status /= Running then
Result.Insert (E.ID);
end if;
end loop;
return Result;
end Get_Not_Running_IDs;
-- Helper function for Elect_Candidates and Check_No_Quota.
-- Performs the actual marking of Entries as being Elected.
procedure Elect
(Index : Positive;
ID : Candidates.CandidateID)
is
Log_Msg : SU.Unbounded_String;
begin
Log_Msg := SU.To_Unbounded_String
(Candidates.Name_And_Party (Cand_Data.Reference (ID)) &
" elected at logfile #" & Int_Image (Next_Log_Num));
Put_Line (Main_Log, SU.To_String (Log_Msg));
if Verbose then
Put_Line (Standard_Error, SU.To_String (Log_Msg));
end if;
Entries.Reference (Index).Status := Elected;
Entries.Reference (Index).Changed := True;
Entries.Reference (Index).Order_Elected := Seats - Vacancies + 1;
Vacancies := Vacancies - 1;
end Elect;
-- Marks all the entries that have quota as elected, and adds a new
-- Transfer for each of them to the transfer queue.
function Elect_Candidates
return Boolean
is
Running : Position_Vectors.Vector := Get_Running_Entry_Positions;
Working_Position : Positive;
Working_ID : Candidates.CandidateID;
Number_Elected : Natural := 0;
begin
Position_Sorting.Sort (Running);
for R in reverse Running.Iterate loop
exit when Running.Reference (R).Total_Votes < Quota;
Working_Position := Position_Vectors.Element (R).Index;
Working_ID := Entries.Reference (Working_Position).ID;
Elect (Working_Position, Working_ID);
Number_Elected := Number_Elected + 1;
Transfers.Append ( (From => Working_ID, Position => Working_Position) );
end loop;
return Number_Elected > 0;
end Elect_Candidates;
-- This step finishes up election processing if all vacancies are filled
-- or if no further running Entries are available to fill them.
function Check_If_Done
return Boolean
is
Total_Still_Running : Natural := 0;
begin
for E of Entries loop
if E.Status = Running then
Total_Still_Running := Total_Still_Running + 1;
end if;
end loop;
if Vacancies = 0 or Total_Still_Running = 0 then
Close (Main_Log);
Work_To_Do := False;
return True;
else
return False;
end if;
end Check_If_Done;
-- Helper function for Transfer_Votes.
-- Sets the Total_Votes, Total_Papers, Vote_Change and Paper_Change for
-- the Entry being transferred from to the appropriate values, and generates
-- a Fraction to use as a transfer value in the actual redistribution.
procedure Adjust_Entry_Votes_And_Papers
(Position : in Positive;
New_Value : out Rationals.Fraction)
is
use type Rationals.Fraction;
Entry_Ref : Entry_Vectors.Reference_Type :=
Entries.Reference (Position);
begin
if Entry_Ref.Status = Excluded then
Entry_Ref.Vote_Change := - Entry_Ref.Total_Votes;
New_Value := 1 / 1;
Entry_Ref.Total_Votes := 0;
else
Entry_Ref.Vote_Change := Quota - Entry_Ref.Total_Votes;
New_Value := (Entry_Ref.Total_Votes - Quota) / Entry_Ref.Total_Votes;
Entry_Ref.Total_Votes := Quota;
end if;
Entry_Ref.Paper_Change := - Entry_Ref.Total_Papers;
Entry_Ref.Total_Papers := 0;
end Adjust_Entry_Votes_And_Papers;
-- Helper function for Transfer_Votes.
-- Performs the actual redistribution of preferences, generating new vote Bundles
-- and adding them to the appropriate Entries. Also keeps a running total of how
-- many papers were lost to fractional losses, and how many papers were *NOT*
-- exhausted.
procedure Redistribute_Papers
(Still_Running : in Position_Vectors.Vector;
Already_Excluded : in Candidates.Containers.CandidateID_Set;
Transfer_From : in Candidates.CandidateID;
Transfer_Value : in Rationals.Fraction;
Fractional_Loss : out Natural;
Not_Exhausted : out Natural)
is
Working_Position : Positive;
Working_ID : Candidates.CandidateID;
New_Bundle : Given_Bundles.Bundle;
Votes_In, Papers_In : Natural;
begin
Fractional_Loss := 0;
Not_Exhausted := 0;
for R in Still_Running.Iterate loop
Working_Position := Still_Running.Constant_Reference (R).Index;
Working_ID := Entries.Constant_Reference (Working_Position).ID;
for B in Pref_Data.Reference (Transfer_From).Iterate loop
Given_Bundles.Transfer
(This => Pref_Data.Reference (Transfer_From).Reference (B),
From => Transfer_From,
To => Working_ID,
Excluded => Already_Excluded,
Value => Transfer_Value,
Result => New_Bundle);
Given_Bundles.Count_Both (New_Bundle, Votes_In, Papers_In);
if Votes_In > 0 then
Pref_Data.Reference (Working_ID).Append (New_Bundle);
declare
Entry_Ref : Entry_Vectors.Reference_Type :=
Entries.Reference (Working_Position);
begin
Entry_Ref.Vote_Change := Entry_Ref.Vote_Change + Votes_In;
Entry_Ref.Paper_Change := Entry_Ref.Paper_Change + Papers_In;
end;
Not_Exhausted := Not_Exhausted + Papers_In;
elsif Papers_In > 0 then
Fractional_Loss := Fractional_Loss + Papers_In;
Not_Exhausted := Not_Exhausted + Papers_In;
end if;
end loop;
declare
Entry_Ref : Entry_Vectors.Reference_Type :=
Entries.Reference (Working_Position);
begin
Entry_Ref.Total_Votes := Entry_Ref.Total_Votes + Entry_Ref.Vote_Change;
Entry_Ref.Total_Papers := Entry_Ref.Total_Papers + Entry_Ref.Paper_Change;
end;
end loop;
Pref_Data.Replace (Transfer_From, Bundle_Containers.Bundle_Vectors.Empty_Vector);
end Redistribute_Papers;
-- Takes the oldest Transfer from the transfer queue and uses the above
-- helper functions to perform it. Only performs a single transfer per call.
function Transfer_Votes
return Boolean
is
Running_Positions : Position_Vectors.Vector;
Not_Considered : Candidates.Containers.CandidateID_Set;
This_Transfer : Pending_Transfer;
This_Value : Rationals.Fraction;
Fractional_Loss, Not_Exhausted : Natural;
begin
if Integer (Transfers.Length) = 0 then
return False;
end if;
Running_Positions := Get_Running_Entry_Positions;
Not_Considered := Get_Not_Running_IDs;
This_Transfer := Transfers.First_Element;
Transfers.Delete_First;
Exhausted.Paper_Change := Entries.Reference (This_Transfer.Position).Total_Papers;
Adjust_Entry_Votes_And_Papers
(Position => This_Transfer.Position,
New_Value => This_Value);
Redistribute_Papers
(Still_Running => Running_Positions,
Already_Excluded => Not_Considered,
Transfer_From => This_Transfer.From,
Transfer_Value => This_Value,
Fractional_Loss => Fractional_Loss,
Not_Exhausted => Not_Exhausted);
Fractional.Paper_Change := Fractional_Loss;
Fractional.Total_Papers := Fractional.Total_Papers + Fractional_Loss;
Exhausted.Paper_Change := Exhausted.Paper_Change - Not_Exhausted;
Exhausted.Total_Papers := Exhausted.Total_Papers + Exhausted.Paper_Change;
return True;
end Transfer_Votes;
-- If the number of running entries is only one more than the number of
-- vacancies remaining to be filled, the entries with the highest vote
-- totals can be elected without further vote transferral.
function Check_No_Quota
return Boolean
is
Running : Position_Vectors.Vector := Get_Running_Entry_Positions;
Working_Position : Positive;
Working_ID : Candidates.CandidateID;
begin
if Integer (Running.Length) > Vacancies + 1 then
return False;
end if;
Position_Sorting.Sort (Running);
for R in reverse Running.Iterate loop
exit when Vacancies = 0;
Working_Position := Position_Vectors.Element (R).Index;
Working_ID := Entries.Reference (Working_Position).ID;
Elect (Working_Position, Working_ID);
end loop;
return True;
end Check_No_Quota;
-- Implements bulk exclusions using applied breakpoints. Entries will be
-- excluded in order of least vote count until the running total of excluded
-- votes is as high as it can go without exceeding the difference between the
-- running entry with the highest vote total and the quota. A minimum of one entry
-- will always be excluded. A new Transfer for each excluded Entry is added
-- to the transfer queue.
-- (Note that this step does not yet implement proper tiebreaker handling.)
function Exclude_Candidates
return Boolean
is
Running : Position_Vectors.Vector := Get_Running_Entry_Positions;
Log_Msg : SU.Unbounded_String;
Working_ID : Candidates.CandidateID;
Working_Position : Positive;
Number_Excluded : Natural := 0;
Votes_Excluded : Natural := 0;
Votes_To_Be_Excluded : Natural;
Applied_Breakpoint : Positive;
begin
Position_Sorting.Sort (Running);
Applied_Breakpoint := Quota - Running.Reference (Running.Last_Index).Total_Votes;
for R in Running.Iterate loop
Votes_To_Be_Excluded := Running.Reference (R).Total_Votes;
exit when Number_Excluded > 0 and Votes_Excluded + Votes_To_Be_Excluded > Applied_Breakpoint;
Working_Position := Running.Reference (R).Index;
Working_ID := Entries.Reference (Working_Position).ID;
Entries.Reference (Working_Position).Status := Excluded;
Entries.Reference (Working_Position).Changed := True;
Transfers.Append ( (From => Working_ID, Position => Working_Position) );
Votes_Excluded := Votes_Excluded + Votes_To_Be_Excluded;
Number_Excluded := Number_Excluded + 1;
end loop;
if Number_Excluded > 1 then
Log_Msg := SU.To_Unbounded_String
("Bulk exclusion of " & Int_Image (Number_Excluded) &
" candidates at logfile #" & Int_Image (Next_Log_Num));
Put_Line (Main_Log, SU.To_String (Log_Msg));
if Verbose then
Put_Line (Standard_Error, SU.To_String (Log_Msg));
end if;
end if;
return Number_Excluded > 0;
end Exclude_Candidates;
-- The main loop of election processing. Each individual step returns
-- a boolean value of whether or not it was applicable and did anything,
-- which allows the use of the if statement.
procedure Run is
begin
while Work_To_Do loop
Write_Log;
-- Clear marked changes in the entry list from
-- previous iterations.
for E of Entries loop
E.Vote_Change := 0;
E.Paper_Change := 0;
E.Changed := False;
end loop;
Fractional.Paper_Change := 0;
Exhausted.Paper_Change := 0;
if not Elect_Candidates and then
not Check_If_Done and then
not Transfer_Votes and then
not Check_No_Quota and then
not Exclude_Candidates
then
-- If all of the above procedures can't do
-- anything then something is wrong.
raise Program_Error;
end if;
end loop;
end Run;
-- A guard function to ensure nobody foolishly tries to run
-- an election before setting it up.
function Is_Properly_Setup
return Boolean is
begin
return Work_To_Do;
end Is_Properly_Setup;
end Election;
|