def create_poly(xs: List[int], p: int) -> nmod_poly:
"""
returns the polynomial (z - x[0]) ... (z - x[N-1]) mod p
"""
ans: nmod_poly = nmod_poly([1], p)
for x in xs:
ans *= nmod_poly([-x, 1], p)
return ans
def ring_generate(irr, p):
power_dict = {(1, ): 0}
element_dict = {0: [1]}
test_poly = flint.nmod_poly([1], 2)
alpha_poly = flint.nmod_poly([0, 1], 2)
for i in range(1, p**irr.degree() - 1):
test_poly = (test_poly * alpha_poly) % irr.poly
coeffs = tuple(int(e) for e in test_poly.coeffs())
if coeffs in power_dict:
return power_dict, element_dict
power_dict[coeffs] = i
element_dict[i] = list(coeffs)
return power_dict, element_dict
def get_phigh(tlist: List[int], s: int, p: int) -> nmod_poly:
"""
return a polynomial object where the caller specfies the highest coefficents
except the highest cofficent which takes the value 1
"""
nzeros: int = s - len(tlist)
coeffs: List[int] = [0] * nzeros
coeffs.extend(tlist)
coeffs.append(1)
return nmod_poly(coeffs, p)
def has_repeated_roots(poly: nmod_poly, prime: int) -> bool:
"""
returns True if the polynomial has repeated roots
"""
if prime < 2 or not isprime(prime):
raise FuzzyError("prime is not prime")
temp: List[int] = [0] * (prime + 1)
temp[-1] = 1
temp[1] = -1
zpoly: nmod_poly = nmod_poly(temp, prime)
result: nmod_poly = zpoly % poly
return result.coeffs() != []
def Berlekamp_Welch(
aList: List[int], # inputs
bList: List[int], # received codeword
k: int,
t: int,
p: int # prime
) -> nmod_poly:
"""
Berlekamp-Welsch-Decoder
This function throws an exception if no solution exists
see https://en.wikipedia.org/wiki/Berlekamp%E2%80%93Welch_algorithm
"""
if len(aList) < 1:
raise FuzzyError("aList is empty")
if len(aList) != len(bList):
raise FuzzyError("bList is empty")
if k < 1 or t < 1:
raise FuzzyError("k={0} and t={1} are not consistent".format(k, t))
if p < 2 or not isprime(p):
raise FuzzyError("p is not prime")
n = len(aList)
# Create the Berlekamp-Welch system of equations
# and store them as an n x n matrix 'm' and a
# constant source vector 'y' of length n
m_entries: List[nmod] = []
y_entries: List[nmod] = []
for i in range(n):
a: int = aList[i]
b: int = bList[i]
apowers: List[nmod] = mod_get_powers(a, k + t, p)
for j in range(k+t):
m_entries.append(apowers[j])
for j in range(t):
m_entries.append(-b * apowers[j])
y_entries.append(b * apowers[t])
m: nmod_mat = nmod_mat(n, n, m_entries, p)
y: nmod_mat = nmod_mat(n, 1, y_entries, p)
# solve the linear system of equations m * x = y for x
try:
x = gauss.solve(m, y).entries()
except gauss.NoSolutionError:
raise FuzzyError("No solution exists")
# create the polynomials Q and E
Qs: List[nmod] = x[:k+t]
Es: List[nmod] = x[k+t:]
Es.append(nmod(1, p))
Q: nmod_poly = nmod_poly(Qs, p)
E: nmod_poly = nmod_poly(Es, p)
Answer: nmod_poly = Q // E
Remainder: nmod_poly = Q - Answer * E
if len(Remainder.coeffs()) > 0:
raise FuzzyError("Remainder is not zero")
return Answer
def from_numpy(arr):
return GF2Poly(flint.nmod_poly([int(e) for e in arr.flat], 2))
def from_list(arr):
return GF2Poly(flint.nmod_poly(arr, 2))
