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primality_test.py
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53 lines (44 loc) · 1.41 KB
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"""
Primality Test
--------------
Implementation of a Primality Test that uses a cache to improve
performance.
"""
from math import sqrt
from algorithms.math.sieve_eratosthenes import eratosthenes
CACHE_LIMIT = 10 ** 6
primes_cache_list = []
primes_cache_bool = []
def is_prime(number, cache=True):
"""
Takes `number` and determines if it is prime.
:param number: The integer to be tested for primality.
:param cache: A boolean to determine if a cache should be used to
improve performance.
:rtype: A boolean that signifies if `number` is prime.
"""
if number < 2:
return False
global primes_cache_list, primes_cache_bool
if cache and len(primes_cache_list) == 0:
primes_cache_list, primes_cache_bool = eratosthenes(
CACHE_LIMIT, return_boolean=True
)
for prime in primes_cache_list:
primes_cache_bool[prime] = True
if number < len(primes_cache_bool):
return primes_cache_bool[number]
sqrt_number = sqrt(number)
for prime in primes_cache_list:
if prime > sqrt_number:
return True
if number % prime == 0:
return False
to_check = 2
if len(primes_cache_list) > 0:
to_check = primes_cache_list[-1] + 1
while to_check <= sqrt_number:
if number % to_check == 0:
return False
to_check += 1
return True