# Source code for diofant.domains.finitefield

"""Implementation of :class:FiniteField class. """

import numbers
import random

from ..core import Dummy, integer_digits
from ..ntheory import isprime, perfect_power
from ..polys.galoistools import gf_irreducible
from ..polys.polyerrors import CoercionFailed
from .field import Field
from .groundtypes import DiofantInteger
from .integerring import GMPYIntegerRing, PythonIntegerRing
from .quotientring import QuotientRingElement
from .simpledomain import SimpleDomain

__all__ = 'FiniteField', 'GMPYFiniteField', 'PythonFiniteField'

_modular_integer_cache = {}

[docs]class FiniteField(Field, SimpleDomain):
"""General class for finite fields. """

is_FiniteField = is_FF = True
is_Numerical = True

has_assoc_Ring = False
has_assoc_Field = True

def __new__(cls, order, dom, modulus=None):
if not (isinstance(order, numbers.Integral) and isprime(order)):
pp = perfect_power(order)
if not pp:
raise ValueError('order must be a prime power, '
'got %s' % order)
mod, deg = pp
else:
mod, deg = order, 1
if modulus is None:
modulus = [1, 0]
else:
deg = len(modulus) - 1
order = mod**deg

if modulus is None:
random.seed(0)
modulus = gf_irreducible(deg, mod, dom)
elif deg != len(modulus) - 1:
raise ValueError('degree of a defining polynomial for the field'
' does not match extension degree')
modulus = tuple(map(dom.dtype, modulus))

mod = dom.convert(mod)

key = order, dom, mod, modulus

obj = super().__new__(cls)

obj.domain = dom
obj.mod = mod
obj.order = order

obj.rep = 'GF(%s)' % obj.order

try:
obj.dtype = _modular_integer_cache[key]
except KeyError:
if deg == 1:
obj.dtype = type("ModularInteger", (ModularInteger,),
{"mod": mod, "domain": dom, "_parent": obj})
else:
ff = dom.finite_field(mod).poly_ring(Dummy('x'))
mod = ff.from_dense(modulus)
if not mod.is_irreducible:
raise ValueError('defining polynomial must be irreducible')
obj.dtype = type("GaloisFieldElement", (GaloisFieldElement,),
{"mod": mod, "domain": ff, "_parent": obj})
_modular_integer_cache[key] = obj.dtype

obj.zero = obj.dtype(0)
obj.one = obj.dtype(1)

return obj

def __hash__(self):
return hash((self.__class__.__name__, self.dtype, self.order, self.domain))

def __eq__(self, other):
"""Returns True if two domains are equivalent. """
return isinstance(other, FiniteField) and \
self.order == other.order and self.domain == other.domain

@property
def characteristic(self):
"""Return the characteristic of this domain. """
return self.mod

[docs]    def to_expr(self, a):
"""Convert a to a Diofant object. """
return DiofantInteger(int(a))

[docs]    def from_expr(self, a):
"""Convert Diofant's Integer to dtype. """
if a.is_Integer:
return self.dtype(self.domain.dtype(int(a)))
elif a.is_Float and int(a) == a:
return self.dtype(self.domain.dtype(int(a)))
else:
raise CoercionFailed("expected an integer, got %s" % a)

def _from_PythonFiniteField(self, a, K0=None):
return self.dtype(self.domain.convert(a.rep, K0.domain))

def _from_PythonIntegerRing(self, a, K0=None):
return self.dtype(self.domain.convert(a, K0))

def _from_PythonRationalField(self, a, K0=None):
if a.denominator == 1:
return self.convert(a.numerator)

def _from_GMPYFiniteField(self, a, K0=None):
return self.dtype(self.domain.convert(a.rep, K0.domain))

def _from_GMPYIntegerRing(self, a, K0=None):
return self.dtype(self.domain.convert(a, K0))

def _from_GMPYRationalField(self, a, K0=None):
if a.denominator == 1:
return self.convert(a.numerator)

def _from_RealField(self, a, K0):
p, q = K0.to_rational(a)

if q == 1:
return self.dtype(self.domain.dtype(p))

[docs]    def is_positive(self, a):
"""Returns True if a is positive. """
return a.rep != 0

[docs]    def is_negative(self, a):
"""Returns True if a is negative. """
return False

[docs]class PythonFiniteField(FiniteField):
"""Finite field based on Python's integers. """

def __new__(cls, order, modulus=None):
return super().__new__(cls, order, PythonIntegerRing(), modulus)

[docs]class GMPYFiniteField(FiniteField):
"""Finite field based on GMPY's integers. """

def __new__(cls, order, modulus=None):
return super().__new__(cls, order, GMPYIntegerRing(), modulus)

class ModularInteger(QuotientRingElement):
"""A class representing a modular integer. """

class GaloisFieldElement(ModularInteger):
def __init__(self, rep):
if isinstance(rep, numbers.Integral):
rep = rep % self.parent.order
rep = integer_digits(rep, self.parent.mod)

if isinstance(rep, (list, tuple)):
rep = self.domain.from_dense(rep)
self.rep = rep = rep % self.mod
else:
super().__init__(rep)

self._int_rep = self.parent.domain.poly_ring(*self.rep.parent.symbols)(dict(self.rep))

def __int__(self):
return int(self._int_rep.eval(0, self.parent.mod))