/*
 * binom_reduce.c
 *
 *  Created on: 18 Jun 2016
 *      Author: johannes
 */

#include <mpi.h>
#include <string.h>
#include <stdio.h>
#include "binom_reduce.h"

void swap(void **a, void **b) {
	void *temp;
	temp = *a;
	*a = *b;
	*b = temp;
}

int Binom_Reduce(const void *sendbuf, void *recvbuf, int count,
		MPI_Datatype datatype, MPI_Op op, int root, MPI_Comm comm) {

	if (root != 0) {
		fprintf(stderr, "Sorry, root!=0 not allowed");
		return -1;
	}

	int r, p, size;
	MPI_Status status;
	void *recv;
	void *reduced;

	MPI_Comm_rank(comm, &r);
	MPI_Comm_size(comm, &p);
	MPI_Type_size(datatype, &size);

	MPI_Alloc_mem(count * size, MPI_INFO_NULL, &recv);
	MPI_Alloc_mem(count * size, MPI_INFO_NULL, &reduced);

	memcpy(reduced, sendbuf, count * size);

	int i = 1;
	while ((r + i) % (2 * i) != 0 && i < p) {
		if (r + i < p) {
			MPI_Recv(recv, count, datatype, r + i, i, comm, &status);
			MPI_Reduce_local(reduced, recv, count, datatype, op);
			swap(&reduced, &recv);
		}
		i <<= 1;
	}

	if (r != root) {
		MPI_Send(reduced, count, datatype, r - i, i, comm);
	} else {
		memcpy(recvbuf, reduced, count * size);
	}

	MPI_Free_mem(reduced);
	MPI_Free_mem(recv);

	return 0;
}