86 lines
1.7 KiB
C
86 lines
1.7 KiB
C
/*
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* bin_reduce.c
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*
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* Created on: 16 Jun 2016
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* Author: johannes
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*/
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#include <stdio.h>
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#include <string.h>
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#include <mpi.h>
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#include "bin_reduce.h"
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int int_log2(int x) {
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int r=0;
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while (x >>= 1) {
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r++;
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}
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return r;
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}
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int Bin_Reduce(const void *sendbuf, void *recvbuf, int count,
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MPI_Datatype datatype, MPI_Op op, int root, MPI_Comm comm) {
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if (root != 0) {
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fprintf(stderr, "Sorry, root!=0 not allowed");
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return -1;
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}
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int r, p, size;
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MPI_Status status;
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MPI_Comm_rank(comm, &r);
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MPI_Comm_size(comm, &p);
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MPI_Type_size(datatype, &size);
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int tree_depth = int_log2(p) + 1;
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int i = 0;
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int depth;
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int parent = 0;
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// maximum possible number of nodes in a subtree with current depth
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int max_nodes = ((1 << tree_depth) - 1) / 2;
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void *recv_left;
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void *recv_right;
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if (r == root) {
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recv_right = recvbuf;
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} else {
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MPI_Alloc_mem(count * size, MPI_INFO_NULL, &recv_right);
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}
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for (depth = 1; i != r; depth++) {
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parent = i;
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if (r > i + max_nodes) {
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i += max_nodes + 1;
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} else {
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i++;
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}
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max_nodes /= 2;
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}
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if (depth != tree_depth && r + 1 < p) {
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MPI_Alloc_mem(count * size, MPI_INFO_NULL, &recv_left);
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MPI_Recv(recv_left, count, datatype, r + 1, 0, comm, &status);
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MPI_Reduce_local(sendbuf, recv_left, count, datatype, op);
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if (r + max_nodes + 1 < p) {
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MPI_Recv(recv_right, count, datatype, r + max_nodes + 1, 0, comm,
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&status);
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MPI_Reduce_local(recv_left, recv_right, count, datatype, op);
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} else {
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memcpy(recv_right, recv_left, count * size);
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}
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MPI_Free_mem(recv_left);
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} else {
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memcpy(recv_right, sendbuf, count * size);
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}
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if (r != root) {
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MPI_Send(recv_right, count, datatype, parent, 0, comm);
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MPI_Free_mem(recv_right);
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}
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return 0;
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}
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