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98 lines
2.0 KiB
C++
98 lines
2.0 KiB
C++
/*
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* C++ Program to Implement Miller Rabin Primality Test
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*/
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#include <iostream>
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#include <cstring>
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#include <cstdlib>
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#define ll long long
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using namespace std;
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/*
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* calculates (a * b) % c taking into account that a * b might overflow
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*/
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ll mulmod(ll a, ll b, ll mod)
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{
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ll x = 0,y = a % mod;
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while (b > 0)
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{
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if (b % 2 == 1)
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{
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x = (x + y) % mod;
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}
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y = (y * 2) % mod;
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b /= 2;
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}
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return x % mod;
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}
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/*
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* modular exponentiation
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*/
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ll modulo(ll base, ll exponent, ll mod)
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{
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ll x = 1;
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ll y = base;
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while (exponent > 0)
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{
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if (exponent % 2 == 1)
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x = (x * y) % mod;
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y = (y * y) % mod;
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exponent = exponent / 2;
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}
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return x % mod;
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}
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/*
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* Miller-Rabin primality test, iteration signifies the accuracy
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*/
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bool Miller(ll p,int iteration)
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{
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if (p < 2)
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{
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return false;
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}
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if (p != 2 && p % 2==0)
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{
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return false;
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}
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ll s = p - 1;
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while (s % 2 == 0)
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{
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s /= 2;
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}
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for (int i = 0; i < iteration; i++)
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{
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ll a = rand() % (p - 1) + 1, temp = s;
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ll mod = modulo(a, temp, p);
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while (temp != p - 1 && mod != 1 && mod != p - 1)
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{
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mod = mulmod(mod, mod, p);
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temp *= 2;
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}
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if (mod != p - 1 && temp % 2 == 0)
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{
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return false;
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}
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}
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return true;
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}
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//Main
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int main()
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{
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int iteration = 5;
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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 (Miller(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;
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}
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/*
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Enter integer to test primality: 127
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127 is prime
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------------------
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(program exited with code: 1)
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Press return to continue
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