93 lines
2.9 KiB
Python
93 lines
2.9 KiB
Python
# pyRCV2: Preferential vote counting
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# Copyright © 2020–2021 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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from pyRCV2.numbers.base import BasePyNum, compatible_types
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import decimal
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_quantize_exp = decimal.Decimal('10') ** -12
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_pos_epsilon = decimal.Decimal('10') ** -6 / decimal.Decimal('2')
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_neg_epsilon = -_pos_epsilon
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def _gfixed_set_dps(dps):
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global _quantize_exp
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_quantize_exp = decimal.Decimal('10') ** -(2 * dps)
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_pos_epsilon = decimal.Decimal('10') ** -dps / decimal.Decimal('2')
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_neg_epsilon = -_pos_epsilon
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class FixedGuarded(BasePyNum):
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"""
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Wrapper for Python Decimal (for fixed-point arithmetic)
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Implements guarded (quasi-exact) fixed-point
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"""
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_py_class = decimal.Decimal # For BasePyNum
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ROUND_DOWN = decimal.ROUND_DOWN
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ROUND_HALF_UP = decimal.ROUND_HALF_UP
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ROUND_HALF_EVEN = decimal.ROUND_HALF_EVEN
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ROUND_UP = decimal.ROUND_UP
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@classmethod
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def _to_impl(cls, value):
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"""Overrides BasePyNum._to_impl"""
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return decimal.Decimal(value).quantize(_quantize_exp)
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@classmethod
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def _truediv_impl(cls, i1, i2):
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"""Overrides BasePyNum._truediv_impl"""
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return (i1 / i2).quantize(_quantize_exp)
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@compatible_types
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def __eq__(self, other):
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"""Overrides BasePyNum.__eq__"""
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diff = self.impl - other.impl
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return diff < _pos_epsilon and diff > _neg_epsilon
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@compatible_types
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def __ne__(self, other):
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"""Overrides BasePyNum.__ne__"""
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return not self.__eq__(other)
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@compatible_types
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def __gt__(self, other):
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"""Overrides BasePyNum.__gt__"""
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diff = self.impl - other.impl
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return diff > _pos_epsilon
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@compatible_types
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def __ge__(self, other):
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"""Overrides BasePyNum.__ge__"""
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diff = self.impl - other.impl
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return diff > _neg_epsilon
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@compatible_types
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def __lt__(self, other):
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"""Overrides BasePyNum.__lt__"""
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diff = self.impl - other.impl
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return diff < _neg_epsilon
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@compatible_types
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def __le__(self, other):
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"""Overrides BasePyNum.__le__"""
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diff = self.impl - other.impl
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return diff < _pos_epsilon
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@compatible_types
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def __itruediv__(self, other):
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"""Overrides BasePyNum.__itruediv__"""
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self.impl = (self.impl / other.impl).quantize(_quantize_exp)
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return self
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def round(self, dps, mode):
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"""Implements BaseNum.round"""
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return FixedGuarded._from_impl(self.impl.quantize(decimal.Decimal('10') ** -dps, mode))
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