33 lines
1.2 KiB
Python
33 lines
1.2 KiB
Python
|
# 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)
|