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