Implement random breaking of ties

html/index.html

@@ -103,15 +103,15 @@
 			</label>
 			<br>
 			<label>
-				Ties (NYI):
+				Ties:
 				<select id="selTies">
-					<option value="backwards_random" selected>Backwards then random</option>
+					<option value="backwards_random" selected>Backwards then random (NYI)</option>
 					<option value="random">Random</option>
 				</select>
 			</label>
 			<label>
 				Random seed:
-				<input type="text" id="txtSeed" value="Not yet implemented">
+				<input type="text" id="txtSeed" value="">
 			</label>
 		</div>
 		
@@ -119,6 +119,7 @@
 		
 		<script src="http://peterolson.github.com/BigRational.js/BigInt_BigRat.min.js"></script>
 		<script src="https://cdn.jsdelivr.net/npm/big.js@6.0.0/big.min.js"></script>
+		<script src="https://cdn.jsdelivr.net/npm/sjcl@1.0.8/sjcl.min.js"></script>
 		<script src="bundle.js"></script>
 		<script src="index.js"></script>
 	</body>

html/index.js

@@ -278,6 +278,14 @@ async function clickCount() {
 			'surplus_order': document.getElementById('selSurplus').value,
 			'ties': document.getElementById('selTies').value
 		},
+		'seed': document.getElementById('txtSeed').value,
 		'data': text
 	});
 }
+
+// Provide a default seed
+if (document.getElementById('txtSeed').value === '') {
+	function pad(x) { if (x < 10) { return '0' + x; } return '' + x; }
+	let d = new Date();
+	document.getElementById('txtSeed').value = d.getFullYear() + pad(d.getMonth() + 1) + pad(d.getDate());
+}

html/worker.js

@@ -16,7 +16,7 @@
     along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
-importScripts('http://peterolson.github.com/BigRational.js/BigInt_BigRat.min.js', 'https://cdn.jsdelivr.net/npm/big.js@6.0.0/big.min.js', 'bundle.js');
+importScripts('http://peterolson.github.com/BigRational.js/BigInt_BigRat.min.js', 'https://cdn.jsdelivr.net/npm/big.js@6.0.0/big.min.js', 'https://cdn.jsdelivr.net/npm/sjcl@1.0.8/sjcl.min.js', 'bundle.js');
 
 onmessage = function(evt) {
 	// Set settings
@@ -50,12 +50,10 @@ onmessage = function(evt) {
 	}
 	
 	if (evt.data.options['ties'] === 'backwards_random') {
-		counter.options['ties'] = [py.pyRCV2.ties.TiesBackwards(), py.pyRCV2.ties.TiesRandom()];
+		counter.options['ties'] = [py.pyRCV2.ties.TiesBackwards(), py.pyRCV2.ties.TiesRandom(evt.data.seed)];
 	} else if (evt.data.options['ties'] === 'random') {
-		counter.options['ties'] = [py.pyRCV2.ties.TiesRandom()];
+		counter.options['ties'] = [py.pyRCV2.ties.TiesRandom(evt.data.seed)];
-	} //else if (evt.data.options['ties'] === 'prompt') {
+	}
-	//	counter.options['ties'] = [py.pyRCV2.ties.TiesPrompt()];
-	//}
 	
 	// Reset
 	let result = counter.reset();

pyRCV2/cli/stv.py

@@ -22,6 +22,8 @@ from pyRCV2.method.base_stv import BaseUIGSTVCounter, BaseWIGSTVCounter
 from pyRCV2.method.wright import WrightSTVCounter
 from pyRCV2.ties import TiesBackwards, TiesPrompt, TiesRandom
 
+import sys
+
 def add_parser(subparsers):
 	parser = subparsers.add_parser('stv', help='single transferable vote')
 	parser.add_argument('file', help='path to BLT file')
@@ -34,6 +36,7 @@ def add_parser(subparsers):
 	parser.add_argument('--surplus-order', '-s', choices=['size', 'order'], default='size', help='whether to distribute surpluses by size or by order of election (default: size)')
 	parser.add_argument('--method', '-m', choices=['wig', 'uig', 'wright'], default='wig', help='method of surpluses and exclusions (default: wig - weighted inclusive Gregory)')
 	parser.add_argument('--ties', '-t', action='append', choices=['backwards', 'prompt', 'random'], default=None, help='how to resolve ties (default: backwards then random)')
+	parser.add_argument('--random-seed', default=None, help='arbitrary string used to seed the RNG for random tie breaking')
 
 def print_step(result):
 	print(result.comment)
@@ -92,7 +95,10 @@ def main(args):
 		elif t == 'prompt':
 			counter.options['ties'].append(TiesPrompt())
 		elif t == 'random':
-			counter.options['ties'].append(TiesRandom())
+			if args.random_seed is None:
+				print('A --random-seed is required to use random tie breaking')
+				sys.exit(1)
+			counter.options['ties'].append(TiesRandom(args.random_seed))
 	
 	# Reset
 	result = counter.reset()

pyRCV2/method/base_stv.py

@@ -19,7 +19,6 @@ __pragma__ = lambda x: None
 from pyRCV2.model import CandidateState, CountCard, CountCompleted, CountStepResult
 from pyRCV2.numbers import Num, Rational
 from pyRCV2.safedict import SafeDict
-from pyRCV2.ties import TiesBackwards, TiesPrompt, TiesRandom
 
 class STVException(Exception):
 	pass
@@ -40,7 +39,7 @@ class BaseSTVCounter:
 			'quota': 'droop', # 'droop', 'droop_exact', 'hare' or 'hare_exact'
 			'quota_criterion': 'geq', # 'geq' or 'gt'
 			'surplus_order': 'size', # 'size' or 'order'
-			'ties': [TiesBackwards(), TiesRandom()]
+			'ties': []
 		}
 		
 		if options is not None:
@@ -335,7 +334,10 @@ class BaseSTVCounter:
 		if len(l) == 1:
 			return l[0]
 		
-		tied = [(c, cc) for c, cc in l if cc.votes == l[0][1].votes]
+		__pragma__('opov')
+		# Do not use (c, cc) for c, cc in ... as this will break equality in JS
+		tied = [x for x in l if x[1].votes == l[0][1].votes]
+		__pragma__('noopov')
 		
 		if len(tied) == 1:
 			return tied[0]
@@ -356,7 +358,10 @@ class BaseSTVCounter:
 		if len(l) == 1:
 			return l[0]
 		
-		tied = [(c, cc) for c, cc in l if cc.votes == l[0][1].votes]
+		__pragma__('opov')
+		# Do not use (c, cc) for c, cc in ... as this will break equality in JS
+		tied = [x for x in l if x[1].votes == l[0][1].votes]
+		__pragma__('noopov')
 		
 		if len(tied) == 1:
 			return tied[0]

pyRCV2/random/__init__.py

@@ -0,0 +1,28 @@
+#   pyRCV2: Preferential vote counting
+#   Copyright © 2020  Lee Yingtong Li (RunasSudo)
+#
+#   This program is free software: you can redistribute it and/or modify
+#   it under the terms of the GNU Affero General Public License as published by
+#   the Free Software Foundation, either version 3 of the License, or
+#   (at your option) any later version.
+#
+#   This program is distributed in the hope that it will be useful,
+#   but WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#   GNU Affero General Public License for more details.
+#
+#   You should have received a copy of the GNU Affero General Public License
+#   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+__pragma__ = lambda x: None
+is_py = False
+__pragma__('skip')
+is_py = True
+__pragma__('noskip')
+
+if is_py:
+	__pragma__('skip')
+	from pyRCV2.random.sharandom_py import SHARandom
+	__pragma__('noskip')
+else:
+	from pyRCV2.random.sharandom_js import SHARandom

pyRCV2/random/sharandom_js.py

@@ -0,0 +1,32 @@
+#   pyRCV2: Preferential vote counting
+#   Copyright © 2020  Lee Yingtong Li (RunasSudo)
+#
+#   This program is free software: you can redistribute it and/or modify
+#   it under the terms of the GNU Affero General Public License as published by
+#   the Free Software Foundation, either version 3 of the License, or
+#   (at your option) any later version.
+#
+#   This program is distributed in the hope that it will be useful,
+#   but WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#   GNU Affero General Public License for more details.
+#
+#   You should have received a copy of the GNU Affero General Public License
+#   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+class SHARandom:
+	MAX_VAL = bigInt(2).pow(256).subtract(1)
+	
+	def __init__(self, seed):
+		self.seed = seed
+		self.ctr = 0
+	
+	def next(self, modulus):
+		val = bigInt(sjcl.codec.hex.fromBits(sjcl.hash.sha256.hash(self.seed + ',' + str(self.ctr))), 16)
+		self.ctr += 1
+		
+		if val.greaterOrEquals(SHARandom.MAX_VAL.divide(modulus).multiply(modulus)):
+			# Discard this value to avoid bias
+			return self.next(modulus)
+		
+		return val.mod(modulus)

pyRCV2/random/sharandom_py.py

@@ -0,0 +1,36 @@
+#   pyRCV2: Preferential vote counting
+#   Copyright © 2020  Lee Yingtong Li (RunasSudo)
+#
+#   This program is free software: you can redistribute it and/or modify
+#   it under the terms of the GNU Affero General Public License as published by
+#   the Free Software Foundation, either version 3 of the License, or
+#   (at your option) any later version.
+#
+#   This program is distributed in the hope that it will be useful,
+#   but WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+#   GNU Affero General Public License for more details.
+#
+#   You should have received a copy of the GNU Affero General Public License
+#   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import hashlib
+
+class SHARandom:
+	MAX_VAL = 2 ** 256 - 1
+	
+	def __init__(self, seed):
+		self.seed = seed
+		self.ctr = 0
+	
+	def next(self, modulus):
+		c = hashlib.sha256()
+		c.update((self.seed + ',' + str(self.ctr)).encode('utf-8'))
+		self.ctr += 1
+		val = int.from_bytes(c.digest(), byteorder='big', signed=False)
+		
+		if val >= (SHARandom.MAX_VAL // modulus) * modulus:
+			# Discard this value to avoid bias
+			return self.next(modulus)
+		
+		return val % modulus

pyRCV2/ties.py

@@ -20,6 +20,8 @@ __pragma__('skip')
 is_py = True
 __pragma__('noskip')
 
+from pyRCV2.random import SHARandom
+
 class TiesPrompt:
 	"""Prompt the user to break ties"""
 	
@@ -71,8 +73,13 @@ class TiesBackwards:
 		raise Exception('Not yet implemented')
 
 class TiesRandom:
+	def __init__(self, seed):
+		self.random = SHARandom(seed)
+	
 	def choose_lowest(self, l):
-		raise Exception('Not yet implemented')
+		l.sort(key=lambda x: x[0].name)
+		return l[self.random.next(len(l))]
 	
 	def choose_highest(self, l):
-		raise Exception('Not yet implemented')
+		l.sort(key=lambda x: x[0].name)
+		return l[self.random.next(len(l))]

pyRCV2/transcrypt.py

@@ -18,6 +18,7 @@ import pyRCV2.blt
 import pyRCV2.model
 import pyRCV2.method, pyRCV2.method.base_stv, pyRCV2.method.wright
 import pyRCV2.numbers
+import pyRCV2.random
 import pyRCV2.ties
 
 __pragma__('js', '{}', 'export {pyRCV2, isinstance, repr, str};')