power

// Iterative C program to compute modular power 
#include <stdio.h> 
  
/* Iterative Function to calculate (x^y)%p in O(log y) */
int power(int x, unsigned int y, int p) 
{ 
    int res = 1;      // Initialize result 
  
    x = x % p;  // Update x if it is more than or  
                // equal to p 
  
    while (y > 0) 
    { 
        // If y is odd, multiply x with result 
        if (y & 1) 
            res = (res*x) % p; 
  
        // y must be even now 
        y = y>>1; // y = y/2 
        x = (x*x) % p;   
    } 
    return res; 
} 
  
// Driver program to test above functions 
int main() 
{ 
   int x = 2; 
   int y = 5; 
   int p = 13; 
   printf("Power is %u", power(x, y, p)); 
   return 0; 
}