55 lines
1.1 KiB
C
55 lines
1.1 KiB
C
|
#include <stdio.h>
|
||
|
|
#include <stdlib.h>
|
||
|
|
|
||
|
|
#define ll long long
|
||
|
|
/*
|
||
|
|
* modular exponentiation
|
||
|
|
*/ll modulo(ll base, ll exponent, ll mod)
|
||
|
|
{
|
||
|
|
ll x = 1;
|
||
|
|
ll y = base;
|
||
|
|
while (exponent > 0)
|
||
|
|
{
|
||
|
|
if (exponent % 2 == 1)
|
||
|
|
x = (x * y) % mod;
|
||
|
|
y = (y * y) % mod;
|
||
|
|
exponent = exponent / 2;
|
||
|
|
}
|
||
|
|
return x % mod;
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Fermat's test for checking primality
|
||
|
|
*/
|
||
|
|
int Fermat(ll p, int iterations)
|
||
|
|
{
|
||
|
|
int i;
|
||
|
|
if (p == 1)
|
||
|
|
{
|
||
|
|
return 0;
|
||
|
|
}
|
||
|
|
for (i = 0; i < iterations; i++)
|
||
|
|
{
|
||
|
|
ll a = rand() % (p - 1) + 1;
|
||
|
|
if (modulo(a, p - 1, p) != 1)
|
||
|
|
{
|
||
|
|
return 0;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
return 1;
|
||
|
|
}
|
||
|
|
/*
|
||
|
|
* Main
|
||
|
|
*/
|
||
|
|
int main()
|
||
|
|
{
|
||
|
|
int iteration = 50;
|
||
|
|
ll num;
|
||
|
|
printf("Enter integer to test primality: ");
|
||
|
|
scanf("%lld", &num);
|
||
|
|
if (Fermat(num, iteration) == 1)
|
||
|
|
printf("%lld is prime ", num);
|
||
|
|
else
|
||
|
|
printf("%lld is not prime ", num);
|
||
|
|
return 0;
|
||
|
|
}
|