Mod9.cpp

#include <cstdio>
#include <omp.h>
#include <cassert>

using namespace std;

constexpr int T_SIZE = 1e8;

// Bitwise operator based function to check multiple of 9
bool isMulOf9(int n) {
	// Base cases
	if (n == 0 || n == 9)
		return true;
	if (n < 9)
		return false;

	// if the number is greater than 9, then do this 
	return isMulOf9((n >> 3) - (n & 7));
};

int main() {
	
	bool r;
	{ // Speed round - int mod
		auto tik = omp_get_wtime();

		for (int i = 0; i < T_SIZE; ++i) {
			r = (i % 9) == 0;
		}

		auto tok = omp_get_wtime();
		printf("int mod : %f\n", (tok - tik));
	}
	{ // Speed round - recursive mod
		auto tik = omp_get_wtime();

		for (int i = 0; i < T_SIZE; ++i) {
			r = isMulOf9(i);
		}

		auto tok = omp_get_wtime();
		printf("rec mod : %f\n", (tok - tik));
	}
	{ // Accuracy round
		for (int i = 0; i < T_SIZE; ++i) {
			assert(((i % 9) == 0) == isMulOf9(i));
		}
		printf("Equivilant Results\n");
	}

	system("pause");
	return 0;
};

Results.txt

int mod : 0.327569
rec mod : 3.301001
Equivilant Results