Cleaned up src/MPI2_message_passing/.

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

diff --git a/src/MPI2_message_passing/hop_again_again.c b/src/MPI2_message_passing/hop_again_again.c
index 36bdb27a1a52dbb4f6922e06cf3abaaf8c4d6e84..00a2163066f9f745a770f0a5e1b8e9d3ccf46b5e 100644 (file)
--- a/src/MPI2_message_passing/hop_again_again.c
+++ b/src/MPI2_message_passing/hop_again_again.c
@@ -1,75 +1,61 @@
-             
-             /*      node identifications      */
+/* passing a message to neighbors, multiple hops */
 
-             /* passing a message to neighbors */
-             /*    multiple hops               */
-                                                   /* Michel Vallieres */
-#include   <stdio.h>
-#include   <mpi.h>
+/* Michel Vallieres */
 
-void permute ( int hop, int *my_number, int my_rank, int size )
+#include <stdio.h>
+#include <mpi.h>
+
+void permute (int hop, int *number, int rank, int size)
 {
-MPI_Status  recv_status;
-int         target_node, from_node;
-int         message;
-                                /* target node */
-   target_node = my_rank + hop;
-   target_node = (target_node +size) % size;
-                                /* from node */
-   from_node = my_rank- hop;
-   from_node = (from_node + size) % size;
-                                /* send info to target node */
-                                /*                          */
-                                /* note: a blocking send    */
-                                /* MPI_Ssend will node lock */
-                                /* in this case             */
-   message = *my_number;
-   MPI_Send(&message, 1, MPI_INT, target_node, 121, MPI_COMM_WORLD);
-                                /* receive new number from the */
-                                /* - from node -               */
-   MPI_Recv(&message, 1, MPI_INT, from_node, 121,
-                            MPI_COMM_WORLD, &recv_status);
-                                 /* update my_number */
-   *my_number = message;
+  MPI_Status  recv_status;
+  int         target_node, from_node, count, tag;
+  int         message;
+
+  count = 1;  /* only sending a single MPI_INT */
+  tag = 123;  /* arbitrary integer tagging the message */
+
+  target_node = (rank + hop + size) % size;       /* target node */
+  from_node = (rank - hop + size) % size;         /* from node */
+  /* The '+ size' ensures positive nodes for hops in the range (-size,size). */
+
+  /* Send info to target node.  Note: a blocking send MPI_Ssend
+   * produces a deadlock in this case. */
+  message = *number;
+  MPI_Send(&message, count, MPI_INT, target_node, tag, MPI_COMM_WORLD);
+
+  /* Receive new number from the from node. */
+  MPI_Recv(&message, count, MPI_INT, from_node, tag,
+          MPI_COMM_WORLD, &recv_status);
+  *number = message;   /* update number */
 }
 
-
 int main (int argc, char *argv[])
 {
-int         my_rank, size;
-MPI_Status  recv_status;
-int         my_number, hop;
-int         target_node, from_node;
-int         message;
+  int rank, size;
+  int number, hop;
 
-   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);
+  number = 2 * rank;                       /* pick a number to pass */
 
-                                /*  def my_number */
-   my_number = 2 * my_rank;
-        
-   printf ( " I am process %d  --  my number is : %d \n",
-                 my_rank, my_number ); 
+  printf ("0: I am process %d  --  my number is %d\n", rank, number);
 
-                                /* first hop */
-   hop = 1;
-   permute( hop, &my_number, my_rank, size );
-   printf ( " I am process %d  --  my number is : %d \n",
-                 my_rank, my_number );
-                                /* second hop */
-   hop = -2;
-   permute( hop, &my_number, my_rank, size );
-   printf ( " I am process %d  --  my number is : %d \n",
-                 my_rank, my_number );
-                                /* third hop */
-   hop = 1;
-   permute( hop, &my_number, my_rank, size );
-   printf ( " I am process %d  --  my number is : %d \n",
-                 my_rank, my_number );
+  /* first hop */
+  hop = 1;
+  permute(hop, &number, rank, size);
+  printf("1: I am process %d  --  my number is %d\n", rank, number);
 
-   MPI_Finalize();
-}
+  /* second hop */
+  hop = -2;
+  permute(hop, &number, rank, size);
+  printf("2: I am process %d  --  my number is %d\n", rank, number);
 
- 
+  /* third hop */
+  hop = 1;
+  permute(hop, &number, rank, size);
+  printf("3: I am process %d  --  my number is %d \n", rank, number);
+
+  MPI_Finalize();
+}