isprime.py

Created by nicolas-patrois

Created on May 30, 2018

413 Bytes

Primality test using random.

from random import randint

def pow(a,n,m):
 p=1
 for _ in range(n):
  p*=a
  p%=m
 return p

def isprime(n):
 d=n-1
 s=0
 while d%2==0:
  s+=1
  d/=2
 for _ in range(5):
  a=randint(2,n-2)
  x=pow(a,d,n)
  if x==1 or x==n-1:
   continue
  c=False
  for _ in range(s-1):
   x=pow(x,2,n)
   if x==1:
    return False
   if x==n-1:
    c=True
    break
  if c:
   continue
  return False
 return True

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