OpenMP test code

OpenMP_test_sample_code.cpp

http://study.marearts.com/2017/05/openmp-test-on-visual-studio.html
#include <stdio.h>
#include <time.h>
#include <omp.h>      //for omp_get_thread_num()

void main()
{
	/////////////////////////////////////////////////////////
	printf("zero case : OpenMP Test (max thread:%d)\n ", omp_get_max_threads() );
	int i;
	omp_set_num_threads(4);         //Set Thread Number
#pragma omp parallel for        
	for (i = 0; i < 8; i++)
	{
		printf("%d Hello, World! Thread ID: %d\n", i,
			omp_get_thread_num());  //thread id
	}

	/////////////////////////////////////////////////////////
	printf("\nfirst case : no threading! \n ");
	double pi = 0.0;
	const int iterationCount = 200000000;
	clock_t startTime = clock();
	for (int i = 0; i < iterationCount; i++)
	{
		pi += 4 * (i % 2 ? -1 : 1) / (2.0 * i + 1.0);
	}
	printf("Elpase Time : %.3lf sec \n", (clock() - startTime) / 1000.);
	printf("pi = %.8f\n", pi);
	/////////////////////////////////////////////////////////

	///////////////////////////////////////////////////////////
	printf("\nsecond case : OpenMP - threading! \n ");
	pi = 0.0;
	startTime = clock();

	#pragma omp parallel for
	for (int i = 0; i < iterationCount; i++)
	{
		pi += 4 * (i % 2 ? -1 : 1) / (2.0 * i + 1.0);
	}
	printf("Elpase Time : %.3lf sec \n", (clock() - startTime) / 1000.);
	printf("pi = %.8f\n", pi);
	/////////////////////////////////////////////////////////

	/////////////////////////////////////////////////////////
	printf("\nthird case : OpenMP - reduction set\n");
	pi = 0.0;
	startTime = clock();

//#pragma omp parallel num_threads(40)
	//{
#pragma omp parallel for reduction(+:pi) //num_threads( omp_get_max_threads() )
		for (int i = 0; i < iterationCount; i++)
		{
			pi += 4 * (i % 2 ? -1 : 1) / (2.0 * i + 1.0);
		}
	//}

	printf("Elpase Time : %.3lf sec \n", (clock() - startTime) / 1000.);
	printf("pi = %.8f\n", pi);
	/////////////////////////////////////////////////////////

	/////////////////////////////////////////////////////////
	printf("\nthird case : OpenMP - critical set\n");
	pi = 0.0;
	startTime = clock();

#pragma omp parallel 
	{
		#pragma omp for 
		for (int i = 0; i < iterationCount; i++)
		{
			#pragma omp critical
			{
				pi += 4 * (i % 2 ? -1 : 1) / (2.0 * i + 1.0);
			}
		}
	}
	printf("Elpase Time : %.3lf sec \n", (clock() - startTime) / 1000.);
	printf("pi = %.8f\n", pi);
	/////////////////////////////////////////////////////////

	/////////////////////////////////////////////////////////
	printf("\nfourth case : OpenMP - private and reduction test\n");
	int num_steps = 200000000;
	double x, step, sum = 0.0;
	step = 1.0 / (double)num_steps;
	startTime = clock();
#pragma omp parallel for private(x) reduction(+:sum)
	for (i = 0; i<num_steps; i++) {
		x = (i + 0.5) * step;
		sum += 4.0 / (1.0 + x*x);
	}
	printf("Elpase Time : %.3lf sec \n", (clock() - startTime) / 1000.);
	printf("PI = %.8f (sum = %.8f)\n", step*sum, sum);
}

http://study.marearts.com/2017/05/openmp-test-on-visual-studio.html