Binom_Reduce funktioniert soweit denk ich, ob kommutativität passt bin

ich nicht sicher

hpc_mpi/src/hpc_mpi.c

@@ -0,0 +1,78 @@
+/*
+ ============================================================================
+ Name        : hpc_mpi.c
+ Author      : 
+ Version     :
+ Copyright   : Your copyright notice
+ Description : Hello MPI World in C 
+ ============================================================================
+ */
+#include <stdio.h>
+#include <string.h>
+#include "mpi.h"
+
+int Binom_Reduce(const void *sendbuf, void *recvbuf, int count,
+		MPI_Datatype datatype, MPI_Op op, int root, MPI_Comm comm);
+
+int main(int argc, char* argv[]) {
+	int my_rank; /* rank of process */
+	int p; /* number of processes */
+
+	/* start up MPI */
+
+	MPI_Init(&argc, &argv);
+
+	/* find out process rank */
+	MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
+
+	/* find out number of processes */
+	MPI_Comm_size(MPI_COMM_WORLD, &p);
+
+	int a = my_rank;
+	int recv;
+
+	Binom_Reduce(&a, &recv, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD);
+
+	if (my_rank == 0) {
+		printf("%i\n", recv);
+	}
+	/* shut down MPI */
+	MPI_Finalize();
+
+	return 0;
+}
+
+int Binom_Reduce(const void *sendbuf, void *recvbuf, int count,
+		MPI_Datatype datatype, MPI_Op op, int root, MPI_Comm comm) {
+	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);
+	if (r != root) {
+		MPI_Alloc_mem(count * size, MPI_INFO_NULL, &reduced);
+	} else {
+		reduced = recvbuf;
+	}
+	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(recv, reduced, count, datatype, op);
+		}
+		i <<= 1;
+	}
+
+	if (r != root) {
+		MPI_Send(reduced, count, datatype, r - i, i, comm);
+	}
+
+	return 0;
+}