This is a non-recursive implementation of exponentiation in O(log(n)) with MOD. Takes up more space as compared to the recursive implementation.

PowMod_nonrecursive.cpp

//non recursive version
int64_t powMod(int64_t a,int64_t power)
{
	if (a==1)
	{
		return 1;
	}
	
	int64_t count=0, answer=1;
	std::vector<int64_t> powerDP;
	powerDP.push_back(a);
	int64_t powerTemp=power>>1;

	while(powerTemp!=0)
	{
		int64_t temp=powerDP.back()*powerDP.back();
		temp=(temp>=MOD)?temp%MOD:temp;
		powerDP.push_back(temp);
		powerTemp=powerTemp>>1;
	}

	while(power!=0)
	{
		if (power & 1)
		{
			answer=answer* powerDP[count];
			answer=(answer>=MOD)?answer%MOD:answer;
			
		}
		power=power>>1;
		count++;
	}
	return answer;
}