[OpenMP] PI 구하기

 

PI 구하는 식 병렬화

 

#include <stdio.h>
#include <omp.h>

static long num_steps = 1000000;
double step;

void Sequential()
{
	double before = omp_get_wtime();

	int i;
	double x, pi, sum = 0.0;

	step = 1.0/(double) num_steps;
	
	for(i=1; i<=num_steps; i++)
	{
		x = (i-0.5) * step;
		sum = sum + 4.0/(1.0 + x*x);
	}
		
	pi = step * sum;
	
	printf("PI : %f\n",pi);
	printf("%f sec Sequential Complete.\n",omp_get_wtime()-before);
}

void openMP()
{
	double before = omp_get_wtime();

	int i;
	double x, pi, sum = 0.0;

	step = 1.0/(double) num_steps;
	#pragma omp parallel shared(sum, num_steps, step) private(i, x)
	{	
		#pragma omp for reduction(+:sum)
		for(i=1; i<=num_steps; i++)
		{
			x = (i-0.5) * step;
			sum = sum + 4.0/(1.0 + x*x);
		}
		
		#pragma omp single
		pi = step * sum;
	}

	printf("PI : %f\n",pi);
	printf("%f sec OpenMP Complete.\n",omp_get_wtime()-before);

}


int main()
{
	openMP();
	Sequential();

	return 0;
}