pi.cpp

gistfile1.txt

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

long long num_steps = 100000000;
double step, table[40];

int main(int argc, char* argv[])
{
	clock_t start, stop;
	double x, pi, sum = 0.0;
	int i,j;
	omp_set_num_threads(2);
	step = 1. / (double)num_steps;

	for (j = 0; j < num_steps; j++){

		start = clock();
		double sum = 0;
#pragma omp parallel
		{
			int id = omp_get_thread_num();
			table[j + id] = 0;
#pragma omp for
			for (i = 0; i < num_steps; i++)
			{
				double x = (i + .5)*step;
				//unieważnienie całej linii danych
				table[j + id] += 4.0 / (1. + x*x);
			}
#pragma omp atomic
			sum += table[j + id];
		}

		pi = sum*step;
		stop = clock();

		printf("Wartosc liczby PI wynosi %15.12f\n", pi);
		printf("Czas przetwarzania wynosi %f sekund\n", ((double)(stop - start) / 1000.0));
	}
	return 0;
}