def zzx_hensel_lift(p, f, f_list, l):
"""Multifactor Hensel lifting.
Given a prime p, polynomial f over Z[x] such that lc(f) is a
unit modulo p, monic pair-wise coprime polynomials f_i over
Z[x] satisfying:
f = lc(f) f_1 ... f_r (mod p)
and a positive integer l, returns a list of monic polynomials
F_1, F_2, ..., F_r satisfying:
f = lc(f) F_1 ... F_r (mod p**l)
F_i = f_i (mod p), i = 1..r
For more details on the implemented algorithm refer to:
[1] J. von zur Gathen, J. Gerhard, Modern Computer Algebra,
First Edition, Cambridge University Press, 1999, pp. 424
"""
r = len(f_list)
lc = zzx_LC(f)
if r == 1:
F = zzx_mul_term(f, igcdex(lc, p**l)[0], 0)
return [zzx_trunc(F, p**l)]
m = p
k = int(r // 2)
d = int(ceil(log(l, 2)))
g = gf_from_int_poly([lc], p)
for f_i in f_list[:k]:
g = gf_mul(g, gf_from_int_poly(f_i, p), p)
h = gf_from_int_poly(f_list[k], p)
for f_i in f_list[k + 1:]:
h = gf_mul(h, gf_from_int_poly(f_i, p), p)
s, t, _ = gf_gcdex(g, h, p)
g = gf_to_int_poly(g, p)
h = gf_to_int_poly(h, p)
s = gf_to_int_poly(s, p)
t = gf_to_int_poly(t, p)
for _ in range(1, d + 1):
(g, h, s, t), m = zzx_hensel_step(m, f, g, h, s, t), m**2
return zzx_hensel_lift(p, g, f_list[:k], l) \
+ zzx_hensel_lift(p, h, f_list[k:], l)
def zzx_hensel_lift(p, f, f_list, l):
"""Multifactor Hensel lifting.
Given a prime p, polynomial f over Z[x] such that lc(f) is a
unit modulo p, monic pair-wise coprime polynomials f_i over
Z[x] satisfying:
f = lc(f) f_1 ... f_r (mod p)
and a positive integer l, returns a list of monic polynomials
F_1, F_2, ..., F_r satisfying:
f = lc(f) F_1 ... F_r (mod p**l)
F_i = f_i (mod p), i = 1..r
For more details on the implemented algorithm refer to:
[1] J. von zur Gathen, J. Gerhard, Modern Computer Algebra,
First Edition, Cambridge University Press, 1999, pp. 424
"""
r = len(f_list)
lc = zzx_LC(f)
if r == 1:
F = zzx_mul_term(f, igcdex(lc, p**l)[0], 0)
return [ zzx_trunc(F, p**l) ]
m = p
k = int(r // 2)
d = int(ceil(log(l, 2)))
g = gf_from_int_poly([lc], p)
for f_i in f_list[:k]:
g = gf_mul(g, gf_from_int_poly(f_i, p), p)
h = gf_from_int_poly(f_list[k], p)
for f_i in f_list[k+1:]:
h = gf_mul(h, gf_from_int_poly(f_i, p), p)
s, t, _ = gf_gcdex(g, h, p)
g = gf_to_int_poly(g, p)
h = gf_to_int_poly(h, p)
s = gf_to_int_poly(s, p)
t = gf_to_int_poly(t, p)
for _ in range(1, d+1):
(g, h, s, t), m = zzx_hensel_step(m, f, g, h, s, t), m**2
return zzx_hensel_lift(p, g, f_list[:k], l) \
+ zzx_hensel_lift(p, h, f_list[k:], l)
def test_gf_from_to_int_poly():
assert gf_from_int_poly([1,0,7,2,20], 5) == [1,0,2,2,0]
assert gf_to_int_poly([1,0,4,2,3], 5) == [1,0,-1,2,-2]
def zzx_zassenhaus(f):
"""Factor square-free polynomials over Z[x]. """
n = zzx_degree(f)
if n == 1:
return [f]
A = zzx_max_norm(f)
b = zzx_LC(f)
B = abs(int(sqrt(n + 1) * 2**n * A * b))
C = (n + 1)**(2 * n) * A**(2 * n - 1)
gamma = int(ceil(2 * log(C, 2)))
prime_max = int(2 * gamma * log(gamma))
for p in xrange(3, prime_max + 1):
if not isprime(p) or b % p == 0:
continue
F = gf_from_int_poly(f, p)
if gf_sqf_p(F, p):
break
l = int(ceil(log(2 * B + 1, p)))
modular = []
for ff in gf_factor_sqf(F, p)[1]:
modular.append(gf_to_int_poly(ff, p))
g = zzx_hensel_lift(p, f, modular, l)
T = set(range(len(g)))
factors, s = [], 1
while 2 * s <= len(T):
for S in subsets(T, s):
G, H = [b], [b]
S = set(S)
for i in S:
G = zzx_mul(G, g[i])
for i in T - S:
H = zzx_mul(H, g[i])
G = zzx_trunc(G, p**l)
H = zzx_trunc(H, p**l)
G_norm = zzx_l1_norm(G)
H_norm = zzx_l1_norm(H)
if G_norm * H_norm <= B:
T = T - S
G = zzx_primitive(G)[1]
f = zzx_primitive(H)[1]
factors.append(G)
b = zzx_LC(f)
break
else:
s += 1
return factors + [f]
def zzx_zassenhaus(f):
"""Factor square-free polynomials over Z[x]. """
n = zzx_degree(f)
if n == 1:
return [f]
A = zzx_max_norm(f)
b = zzx_LC(f)
B = abs(int(sqrt(n+1)*2**n*A*b))
C = (n+1)**(2*n)*A**(2*n-1)
gamma = int(ceil(2*log(C, 2)))
prime_max = int(2*gamma*log(gamma))
for p in xrange(3, prime_max+1):
if not isprime(p) or b % p == 0:
continue
F = gf_from_int_poly(f, p)
if gf_sqf_p(F, p):
break
l = int(ceil(log(2*B + 1, p)))
modular = []
for ff in gf_factor_sqf(F, p)[1]:
modular.append(gf_to_int_poly(ff, p))
g = zzx_hensel_lift(p, f, modular, l)
T = set(range(len(g)))
factors, s = [], 1
while 2*s <= len(T):
for S in subsets(T, s):
G, H = [b], [b]
S = set(S)
for i in S:
G = zzx_mul(G, g[i])
for i in T-S:
H = zzx_mul(H, g[i])
G = zzx_trunc(G, p**l)
H = zzx_trunc(H, p**l)
G_norm = zzx_l1_norm(G)
H_norm = zzx_l1_norm(H)
if G_norm*H_norm <= B:
T = T - S
G = zzx_primitive(G)[1]
f = zzx_primitive(H)[1]
factors.append(G)
b = zzx_LC(f)
break
else:
s += 1
return factors + [f]
