Fermat Primality Test in C++

This C++ Program demonstrates the implementation of Fermat Primality Test.

Here is source code of the C++ Program to demonstrate the implementation of Fermat Primality Test. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/* 
```

 * C++ Program to Implement Fermat Primality Test

```
 */
```
```
#include <cstring>
```
```
#include <iostream>
```
```
#include <cstdlib>
```
```
#define ll long long
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```
using namespace std;
```
```
/* 
```
```
 * modular exponentiation
```
```
 */
```
```
ll modulo(ll base, ll exponent, ll mod)
```
```
{
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```
    ll x = 1;
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    ll y = base;
```
```
    while (exponent > 0)
```
```
    {
```
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        if (exponent % 2 == 1)
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            x = (x * y) % mod;
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```
        y = (y * y) % mod;
```
```
        exponent = exponent / 2;
```
```
    }
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```
    return x % mod;
```
```
}
```
```
 
```
```
/* 
```

 * Fermat's test for checking primality

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 */
```
```
bool Fermat(ll p, int iterations)
```
```
{
```
```
    if (p == 1)
```
```
    {
```
```
        return false;
```
```
    }
```

    for (int i = 0; i < iterations; i++)

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    {
```
```
        ll a = rand() % (p - 1) + 1; 
```
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        if (modulo(a, p - 1, p) != 1)
```
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        { 
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            return false;
```
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        }
```
```
    }
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    return true;
```
```
}
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```
/* 
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```
 * Main
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```
 */
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int main()
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```
{
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    int iteration = 50;
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    ll num;
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    cout<<"Enter integer to test primality: ";

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    cin>>num;
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    if (Fermat(num, iteration))
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        cout<<num<<" is prime"<<endl;
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```
    else
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        cout<<num<<" is not prime"<<endl;

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    return 0;
```
```
}
```

$ g++ fermat_primality.cpp
$ a.out
 
Enter integer to test primality: 479001599
479001599 is prime
 
------------------
(program exited with code: 1)
Press return to continue

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