Parallel programming final exam 3rd question. C parallel program that calculate trapezoidal area via OpenMP.

calculateTrapAreaOpenMP.c

/*
Paralel Programlama Final Soruları
Soru 3)	Argüman olarak n sayısını alan ve geriye trapezoidal alanı döndüren C programını OPENMP ile yazınız.
	n in tek olduğu durumlar göz önüne alınmalıdır.
	
	Compile:  gcc -g -Wall -o calculateTrapAreaOpenMP calculateTrapAreaOpenMP.c -lm -lpthread
	Run:      ./calculateTrapAreaOpenMP <number of threads> <n>
	
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*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <omp.h>

#define A_POINT 0.0
#define B_POINT 0.8

double f(double x) {
	return 0.2 + 25 * x + -200 * pow(x, 2) + 675 * pow(x, 3) - 900 * pow(x, 4) + 400 * pow(x, 5);
}

void Trap(int n, double* global_result_p) {
	double  h, x, my_result, tempRemainder;
	double  local_a, local_b;
	int  i, local_n;
	int my_rank = omp_get_thread_num();
	int thread_count = omp_get_num_threads();

	h = (B_POINT - A_POINT) / n;

	if (n % thread_count == 0) {
		local_n = n / thread_count;
		local_a = A_POINT + my_rank*local_n*h;
		local_b = local_a + local_n*h;
	}
	else {
		tempRemainder = n % thread_count;
		local_n = (n - tempRemainder) / thread_count;
		local_a = A_POINT + my_rank*local_n*h;
		if (my_rank == thread_count - 1) {
			local_b = local_a + local_n*h + tempRemainder;
		}
		else {
			local_b = local_a + local_n*h;
		}
	}

	my_result = (f(local_a) + f(local_b)) / 2.0;
	for (i = 1; i <= local_n - 1; i++) {
		x = local_a + i*h;
		my_result += f(x);
	}
	my_result = my_result*h;

#	pragma omp critical 
	*global_result_p += my_result;
}

int main(int argc, char* argv[]) {
	int n = 10;
	int thread_count = 10;
	double  global_result = 0.0;

	//sınav için gerekli: değerleri konsoldan alıyoruz.
	//thread_count = strtol(argv[1], NULL, 10); 
	//n = strtoll(argv[2], NULL, 10);

#	pragma omp parallel num_threads(thread_count) 
	Trap(n, &global_result);

	printf("%lf\n", global_result);

	system("PAUSE");
	return 0;
}