def williams_pp1(n):
if isprime(n): return n
m = ispower(n)
if m: return m
for v in count(1):
for p in primegen():
e = ilog(isqrt(n), p)
if e == 0: break
for _ in xrange(e): v = mlucas(v, p, n)
g = gcd(v - 2, n)
if 1 < g < n: return g
if g == n: break
def introot(n, r=2):
if n < 0: return None if r%2 == 0 else -introot(-n, r)
if n < 2: return n
if r == 2: return isqrt(n)
lower, upper = 0, n
while lower != upper - 1:
mid = (lower + upper) / 2
m = mid**r
if m == n: return mid
elif m < n: lower = mid
elif m > n: upper = mid
return lower
def primefac(n, trial_limit=1000, rho_rounds=42000, verbose=False,
methods=(pollardRho_brent, pollard_pm1, williams_pp1, ecm, mpqs)):
# Obtains a complete factorization of n, yielding the prime factors as they are obtained.
# If the user explicitly specifies a splitting method, use that method. Otherwise,
# 1. Pull out small factors with trial division.
# TODO: a few rounds of Fermat's method?
# 2. Do a few rounds of Pollard's Rho algorithm.
# TODO: a few rounds of ECM by itself?
# TODO: a certain amount of P-1?
# 3. Launch multifactor on the remainder. Multifactor has enough overhead that we want to be fairly sure that rho isn't
# likely to yield new factors soon. The default value of rho_rounds=42000 seems good for that but is probably overkill.
if n < 2: return
if isprime(n): yield n; return
factors, nroot = [], isqrt(n)
for p in primegen(): # Note that we remove factors of 2 whether the user wants to or not.
if n%p == 0:
while n%p == 0:
yield p
n /= p
nroot = isqrt(n)
if isprime(n):
yield n
return
if p > nroot:
if n != 1: yield n
return
if p >= trial_limit: break
if isprime(n): yield n; return
if rho_rounds == "inf":
factors = [n]
while len(factors) != 0:
n = min(factors)
factors.remove(n)
f = pollardRho_brent(n)
if isprime(f): yield f
else: factors.append(f)
n /= f
if isprime(n): yield n
else: factors.append(n)
return
factors, difficult = [n], []
while len(factors) != 0:
rhocount = 0
n = factors.pop()
try:
g = n
while g == n:
x, c, g = randrange(1, n), randrange(1, n), 1
y = x
while g==1:
if rhocount >= rho_rounds: raise Exception
rhocount += 1
x = (x**2 + c) % n
y = (y**2 + c) % n
y = (y**2 + c) % n
g = gcd(x-y, n)
# We now have a nontrivial factor g of n. If we took too long to get here, we're actually at the except statement.
if isprime(g): yield g
else: factors.append(g)
n /= g
if isprime(n): yield n
else: factors.append(n)
except Exception: difficult.append(n) # Factoring n took too long. We'll have multifactor chug on it.
factors = difficult
while len(factors) != 0:
n = min(factors)
factors.remove(n)
f = multifactor(n, methods=methods, verbose=verbose)
if isprime(f): yield f
else: factors.append(f)
n /= f
if isprime(n): yield n
else: factors.append(n)
def mpqs(n):
# When the bound proves insufficiently large, we throw out all our work and start over.
# TODO: When this happens, get more data, but don't trash what we already have.
# TODO: Rewrite to get a few more relations before proceeding to the linear algebra.
# TODO: When we need to increase the bound, what is the optimal increment?
# Special cases: this function poorly handles primes and perfect powers:
m = ispower(n)
if m: return m
if isprime(n): return n
root_n, root_2n = isqrt(n), isqrt(2*n)
bound = ilog(n**6, 10)**2 # formula chosen by experiment
while True:
try:
prime, mod_root, log_p, num_prime = [], [], [], 0
# find a number of small primes for which n is a quadratic residue
p = 2
while p < bound or num_prime < 3:
leg = legendre(n%p, p)
if leg == 1:
prime += [p]
mod_root += [mod_sqrt(n, p)] # the rhs was [int(mod_sqrt(n, p))]. If we get errors, put it back.
log_p += [log(p, 10)]
num_prime += 1
elif leg == 0: return p
p = nextprime(p)
x_max = len(prime)*60 # size of the sieve
m_val = (x_max * root_2n) >> 1 # maximum value on the sieved range
# fudging the threshold down a bit makes it easier to find powers of primes as factors
# as well as partial-partial relationships, but it also makes the smoothness check slower.
# there's a happy medium somewhere, depending on how efficient the smoothness check is
thresh = log(m_val, 10) * 0.735
# skip small primes. they contribute very little to the log sum
# and add a lot of unnecessary entries to the table
# instead, fudge the threshold down a bit, assuming ~1/4 of them pass
min_prime = mpz(thresh*3)
fudge = sum(log_p[i] for i,p in enumerate(prime) if p < min_prime)/4
thresh -= fudge
smooth, used_prime, partial = [], set(), {}
num_smooth, num_used_prime, num_partial, num_poly, root_A = 0, 0, 0, 0, isqrt(root_2n / x_max)
while num_smooth <= num_used_prime:
# find an integer value A such that:
# A is =~ sqrt(2*n) / x_max
# A is a perfect square
# sqrt(A) is prime, and n is a quadratic residue mod sqrt(A)
while True:
root_A = nextprime(root_A)
leg = legendre(n, root_A)
if leg == 1: break
elif leg == 0: return root_A
A = root_A**2
# solve for an adequate B
# B*B is a quadratic residue mod n, such that B*B-A*C = n
# this is unsolvable if n is not a quadratic residue mod sqrt(A)
b = mod_sqrt(n, root_A)
B = (b + (n - b*b) * modinv(b + b, root_A))%A
C = (B*B - n) / A # B*B-A*C = n <=> C = (B*B-n)/A
num_poly += 1
# sieve for prime factors
sums, i = [0.0]*(2*x_max), 0
for p in prime:
if p < min_prime:
i += 1
continue
logp = log_p[i]
inv_A = modinv(A, p)
# modular root of the quadratic
a, b, k = mpz(((mod_root[i] - B) * inv_A)%p), mpz(((p - mod_root[i] - B) * inv_A)%p), 0
while k < x_max:
if k+a < x_max: sums[k+a] += logp
if k+b < x_max: sums[k+b] += logp
if k:
sums[k-a+x_max] += logp
sums[k-b+x_max] += logp
k += p
i += 1
# check for smooths
i = 0
for v in sums:
if v > thresh:
x, vec, sqr = x_max-i if i > x_max else i, set(), []
# because B*B-n = A*C
# (A*x+B)^2 - n = A*A*x*x+2*A*B*x + B*B - n
# = A*(A*x*x+2*B*x+C)
# gives the congruency
# (A*x+B)^2 = A*(A*x*x+2*B*x+C) (mod n)
# because A is chosen to be square, it doesn't need to be sieved
val = sieve_val = (A*x + 2*B)*x + C
if sieve_val < 0: vec, sieve_val = {-1}, -sieve_val
for p in prime:
while sieve_val%p == 0:
if p in vec: sqr += [p] # track perfect sqr facs to avoid sqrting something huge at the end
vec ^= {p}
sieve_val = mpz(sieve_val / p)
if sieve_val == 1: # smooth
smooth += [(vec, (sqr, (A*x+B), root_A))]
used_prime |= vec
elif sieve_val in partial:
# combine two partials to make a (xor) smooth
# that is, every prime factor with an odd power is in our factor base
pair_vec, pair_vals = partial[sieve_val]
sqr += list(vec & pair_vec) + [sieve_val]
vec ^= pair_vec
smooth += [(vec, (sqr + pair_vals[0], (A*x+B)*pair_vals[1], root_A*pair_vals[2]))]
used_prime |= vec
num_partial += 1
else: partial[sieve_val] = (vec, (sqr, A*x+B, root_A)) # save partial for later pairing
i += 1
num_smooth, num_used_prime = len(smooth), len(used_prime)
used_prime = sorted(list(used_prime))
# set up bit fields for gaussian elimination
masks, mask, bitfields = [], 1, [0]*num_used_prime
for vec, vals in smooth:
masks += [mask]
i = 0
for p in used_prime:
if p in vec: bitfields[i] |= mask
i += 1
mask <<= 1
# row echelon form
offset = 0
null_cols = []
for col in xrange(num_smooth):
pivot = bitfields[col-offset] & masks[col] == 0 # This occasionally throws IndexErrors.
# TODO: figure out why it throws errors and fix it.
for row in xrange(col+1-offset, num_used_prime):
if bitfields[row] & masks[col]:
if pivot: bitfields[col-offset], bitfields[row], pivot = bitfields[row], bitfields[col-offset], False
else: bitfields[row] ^= bitfields[col-offset]
if pivot:
null_cols += [col]
offset += 1
# reduced row echelon form
for row in xrange(num_used_prime):
mask = bitfields[row] & -bitfields[row] # lowest set bit
for up_row in xrange(row):
if bitfields[up_row] & mask: bitfields[up_row] ^= bitfields[row]
# check for non-trivial congruencies
# TODO: if none exist, check combinations of null space columns...
# if _still_ none exist, sieve more values
for col in null_cols:
all_vec, (lh, rh, rA) = smooth[col]
lhs = lh # sieved values (left hand side)
rhs = [rh] # sieved values - n (right hand side)
rAs = [rA] # root_As (cofactor of lhs)
i = 0
for field in bitfields:
if field & masks[col]:
vec, (lh, rh, rA) = smooth[i]
lhs += list(all_vec & vec) + lh
all_vec ^= vec
rhs += [rh]
rAs += [rA]
i += 1
factor = gcd(listprod(rAs)*listprod(lhs) - listprod(rhs), n)
if 1 < factor < n: return factor
except IndexError: pass
bound *= 1.2
def isprime(n, tb=(3,5,7,11), eb=(2,), mrb=()): # TODO: more streamlining
# tb: trial division basis
# eb: Euler's test basis
# mrb: Miller-Rabin basis
# This test suite's first false positve is unknown but has been shown to be greater than 2**64.
# Infinitely many are thought to exist.
if n%2 == 0 or n < 13 or n == isqrt(n)**2: return n in (2, 3, 5, 7, 11) # Remove evens, squares, and numbers less than 13
if any(n%p == 0 for p in tb): return n in tb # Trial division
for b in eb: # Euler's test
if b >= n: continue
if not pow(b, n-1, n) == 1: return False
r = n - 1
while r%2 == 0: r /= 2
c = pow(b, r, n)
if c == 1: continue
while c != 1 and c != n-1: c = pow(c, 2, n)
if c == 1: return False
s, d = pfactor(n)
if not sprp(n, 2, s, d): return False
if n < 2047: return True
if n >= 3825123056546413051: # BPSW has two phases: SPRP with base 2 and SLPRP. We just did the SPRP; now we do the SLPRP:
d = 5
while True:
if gcd(d, n) > 1:
p, q = 0, 0
break
if jacobi(d, n) == -1:
p, q = 1, (1 - d) / 4
break
d = -d - 2*d/abs(d)
if p == 0: return n == d
s, t = pfactor(n + 2)
u, v, u2, v2, m = 1, p, 1, p, t/2
k = q
while m > 0:
u2, v2, q = (u2*v2)%n, (v2*v2-2*q)%n, (q*q)%n
if m%2 == 1:
u, v = u2*v+u*v2, v2*v+u2*u*d
if u%2 == 1: u += n
if v%2 == 1: v += n
u, v, k = (u/2)%n, (v/2)%n, (q*k)%n
m /= 2
if (u == 0) or (v == 0): return True
for i in xrange(1, s):
v, k = (v*v-2*k)%n, (k*k)%n
if v == 0: return True
return False
if not mrb:
if n < 1373653: mrb = [3]
elif n < 25326001: mrb = [3,5]
elif n < 3215031751: mrb = [3,5,7]
elif n < 2152302898747: mrb = [3,5,7,11]
elif n < 3474749660383: mrb = [3,5,6,11,13]
elif n < 341550071728321: mrb = [3,5,7,11,13,17] # This number is also a false positive for primes(19+1).
elif n < 3825123056546413051: mrb = [3,5,7,11,13,17,19,23] # Also a false positive for primes(31+1).
return all(sprp(n, b, s, d) for b in mrb) # Miller-Rabin
