// ==================================================================
//      Author: Jean-Michel RICHER
//       Email: jean-michel.richer@univ-angers.fr
// Institution: LERIA, Faculty of Science
//              University of Angers, France
// ==================================================================

#include <iostream>
#include <iomanip>
using namespace std;

typedef double real;

/* ==================================================================
 * SUBPROGRAM
 *
 *		real sum_reduction( real *t, int size );
 *
 * WHAT
 *
 *  Perform sum of values of the array @param(t) of
 *  @param(size) elements
 *
 * HOW
 *
 *	Simply iterate and sum each value.
 *
 * PARAMETERS
 *
 *	@paramdef(real, t) : array
 *  @paramdef(int, size) : size of the array
 *
 * ==================================================================
 */
real sum_reduction(real *t, int size)
{

	real total = 0.0;

	for (int i = 0; i < size; ++i)
	{
		total += t[i];
	}

	return total;
}

/* ==================================================================
 * SUBPROGRAM
 *
 *		real parallel_sum_reduction( real *t, int size );
 *
 * WHAT
 *
 *  Perform sum of values of the array @param(t) of
 *  @param(size) elements
 *
 * HOW
 *
 *	Simply iterate and sum each value but use parallelism
 *
 * PARAMETERS
 *
 *	@paramdef(real, t) : array
 *  @paramdef(int, size) : size of the array
 *
 * ==================================================================
 */
real parallel_sum_reduction(real *t, int size)
{

	real total = 0.0;

// OpenMP directive for parallelization
#pragma omp parallel for reduction(+ : total)
	for (int i = 0; i < size; ++i)
	{
		total += t[i];
	}

	return total;
}

/* ==================================================================
 * SUBPROGRAM
 *
 * 		int main(int argc, char *argv[])
 *
 * WHAT
 *
 *   Main program that repeats 100 times the reduction and sums all
 *   results.
 *   Expected result is sum=10000000000.00
 *
 * PARAMETERS
 *
 *	@paramdef(int,argc) : number of command line arguments
 *  @paramdef(char **, argv) : command line arguments as C-strings
 *
 * ==================================================================
 */
int main(int argc, char *argv[])
{

	int method = 1;

	if (argc > 1)
	{
		method = std::stoi(argv[1]);
	}
	// maximum number of values in the array
	const int MAX_VALUES = 100'000'000;
	// array of reals
	real *data;

	// allocate array
	data = new real[MAX_VALUES];

	// fill array
	for (int i = 0; i < MAX_VALUES; ++i)
	{
		data[i] = 1.0;
	}

	real sum = 0;

	for (int r = 1; r <= 100; ++r)
	{
		if (method == 1)
		{
			sum += sum_reduction(data, MAX_VALUES);
		}
		else
		{
			sum += parallel_sum_reduction(data, MAX_VALUES);
		}
	}

	// print result

	cout << "sum=" << std::fixed << std::setprecision(2) << sum << endl;

	return EXIT_SUCCESS;
}