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"""Created by Nathan Damon, @bizzfitch on github
>>> test_miller_rabin()
"""
def miller_rabin(n, allow_probable=False):
"""Deterministic Miller-Rabin algorithm for primes ~< 3.32e24.
Uses numerical analysis results to return whether or not the passed number
is prime. If the passed number is above the upper limit, and
allow_probable is True, then a return value of True indicates that n is
probably prime. This test does not allow False negatives- a return value
of False is ALWAYS composite.
Parameters
----------
n : int
The integer to be tested. Since we usually care if a number is prime,
n < 2 returns False instead of raising a ValueError.
allow_probable: bool, default False
Whether or not to test n above the upper bound of the deterministic test.
Raises
------
ValueError
Reference
---------
https://en.wikipedia.org/wiki/Miller%E2%80%93Rabin_primality_test
"""
if n == 2:
return True
if not n % 2 or n < 2:
return False
if n > 5 and n % 10 not in (1, 3, 7, 9): # can quickly check last digit
return False
if n > 3_317_044_064_679_887_385_961_981 and not allow_probable:
raise ValueError(
"Warning: upper bound of deterministic test is exceeded. "
"Pass allow_probable=True to allow probabilistic test. "
"A return value of True indicates a probable prime."
)
# array bounds provided by analysis
bounds = [
2_047,
1_373_653,
25_326_001,
3_215_031_751,
2_152_302_898_747,
3_474_749_660_383,
341_550_071_728_321,
1,
3_825_123_056_546_413_051,
1,
1,
318_665_857_834_031_151_167_461,
3_317_044_064_679_887_385_961_981,
]
primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41]
for idx, _p in enumerate(bounds, 1):
if n < _p:
# then we have our last prime to check
plist = primes[:idx]
break
d, s = n - 1, 0
# break up n -1 into a power of 2 (s) and
# remaining odd component
# essentially, solve for d * 2 ** s == n - 1
while d % 2 == 0:
d //= 2
s += 1
for prime in plist:
pr = False
for r in range(s):
m = pow(prime, d * 2 ** r, n)
# see article for analysis explanation for m
if (r == 0 and m == 1) or ((m + 1) % n == 0):
pr = True
# this loop will not determine compositeness
break
if pr:
continue
# if pr is False, then the above loop never evaluated to true,
# and the n MUST be composite
return False
return True
def test_miller_rabin():
"""Testing a nontrivial (ends in 1, 3, 7, 9) composite
and a prime in each range.
"""
assert not miller_rabin(561)
assert miller_rabin(563)
# 2047
assert not miller_rabin(838_201)
assert miller_rabin(838_207)
# 1_373_653
assert not miller_rabin(17_316_001)
assert miller_rabin(17_316_017)
# 25_326_001
assert not miller_rabin(3_078_386_641)
assert miller_rabin(3_078_386_653)
# 3_215_031_751
assert not miller_rabin(1_713_045_574_801)
assert miller_rabin(1_713_045_574_819)
# 2_152_302_898_747
assert not miller_rabin(2_779_799_728_307)
assert miller_rabin(2_779_799_728_327)
# 3_474_749_660_383
assert not miller_rabin(113_850_023_909_441)
assert miller_rabin(113_850_023_909_527)
# 341_550_071_728_321
assert not miller_rabin(1_275_041_018_848_804_351)
assert miller_rabin(1_275_041_018_848_804_391)
# 3_825_123_056_546_413_051
assert not miller_rabin(79_666_464_458_507_787_791_867)
assert miller_rabin(79_666_464_458_507_787_791_951)
# 318_665_857_834_031_151_167_461
assert not miller_rabin(552_840_677_446_647_897_660_333)
assert miller_rabin(552_840_677_446_647_897_660_359)
# 3_317_044_064_679_887_385_961_981
# upper limit for probabilistic test
if __name__ == "__main__":
test_miller_rabin()