Cleaned up src/MPI2_message_passing/.

[parallel_computing.git] / src / MPI2_message_passing / ring.c

diff --git a/src/MPI2_message_passing/ring.c b/src/MPI2_message_passing/ring.c
index c897d96077c0720c15fe9075006b04d7e6d969fb..e03a875b7cdc7599620d853c2cf13c76ec17d39b 100644 (file)
--- a/src/MPI2_message_passing/ring.c
+++ b/src/MPI2_message_passing/ring.c
@@ -1,70 +1,62 @@
-
 /************************************************************************
- * This file has been written as a sample solution to an exercise in a 
+ * This file has been written as a sample solution to an exercise in a
  * course given at the Edinburgh Parallel Computing Centre. It is made
  * freely available with the understanding that every copy of this file
  * must include this header and that EPCC takes no responsibility for
  * the use of the enclosed teaching material.
  *
- * Author:      Joel Malard     
+ * Author:      Joel Malard
  *
  * Contact:     epcc-tec@epcc.ed.ac.uk
  *
- * Purpose:     A program to try out non-blocking point-to-point 
+ * Purpose:     A program to try out non-blocking point-to-point
  *              communications.
  *
  * Contents:    C source code.
  *
  ************************************************************************/
 
-#include       <stdio.h>
-#include       <mpi.h>
-#define tag_right 201
-#define tag_left  102
+#include <stdio.h>
+#include <mpi.h>
+
+#define TAG_RIGHT 123
 
 int main (int argc, char *argv[])
 {
-int ierror, rank, my_rank, size;
-int right, left;
-int other, sum, i;
-int message;
+  int ierror, rank, size;
+  int right, left, count, i;
+  int message, sum;
 
-MPI_Status  send_status;
-MPI_Status  recv_status;
-MPI_Request request;
+  MPI_Status  send_status;
+  MPI_Status  recv_status;
+  MPI_Request request;
 
-    MPI_Init(&argc, &argv);
+  MPI_Init(&argc, &argv);
+  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
+  MPI_Comm_size(MPI_COMM_WORLD, &size);
 
-    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
-    MPI_Comm_size(MPI_COMM_WORLD, &size);
+  count = 1;                        /* only sending a single MPI_INT */
+  right = (rank + 1) % size;
+  left = (rank - 1 + size) % size;  /* the '+ size' ensures 'left >= 0'. */
 
-    right = my_rank + 1;
-    if (right == size) right = 0;
+  sum = 0;
+  message = rank;
 
-    left = my_rank - 1;
-    if (left == -1) left = size-1;
+  for (i=0; i < size; i++) {
+    /* Issend because? */
+    MPI_Issend(&message, count, MPI_INT, right, TAG_RIGHT,
+              MPI_COMM_WORLD, &request);
 
-    sum = 0;
-    message = my_rank;
+    MPI_Recv(&message, count, MPI_INT, left, TAG_RIGHT,
+            MPI_COMM_WORLD, &recv_status);
 
-    for( i = 0; i < size; i++) {
+    /* Wait because? */
+    MPI_Wait(&request, &send_status);
 
-        MPI_Issend(&message, 1, MPI_INT, right, tag_right,
-                   MPI_COMM_WORLD, &request);
-    
-        MPI_Recv(&other, 1, MPI_INT, left, tag_right,
-                 MPI_COMM_WORLD, &recv_status);
-    
-        MPI_Wait(&request, &send_status);
-    
-        sum = sum + other;
-        message = other;
-    
-    }
+    sum += message;
+  }
 
-    printf ("PE%d:\tSum = %d\n", my_rank, sum);
-
-    MPI_Finalize();
+  printf ("PE%d:\tSum = %d\n", rank, sum);
 
+  MPI_Finalize();
 }
-