bitree

a/bitree.cc

@@ -19,19 +19,29 @@ int main(int argc, char *argv[]) {
   // sum
   int base = 1;
   for (int i = 0; i < steps; ++i) {
-    int group = rank / base;
-    int offset = rank % base;
-    int target = (group % 2 ? group - 1 : group + 1) * base + offset;
-    if (rank < target) {
-      MPI_Send(reinterpret_cast<void*>(&send), 1, MPI_INT, target, target, MPI_COMM_WORLD);
-      MPI_Recv(reinterpret_cast<void*>(&recv), 1, MPI_INT, target, rank, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
-    } else {
-      MPI_Recv(reinterpret_cast<void*>(&recv), 1, MPI_INT, target, rank, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
-      MPI_Send(reinterpret_cast<void*>(&send), 1, MPI_INT, target, target, MPI_COMM_WORLD);
+    if (rank % base == 0) {
+      int b = base * 2;
+      if (rank % b == 0) { // recv
+        MPI_Recv(&recv, 1, MPI_INT, rank + base, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+      } else { // send
+        MPI_Send(&send, 1, MPI_INT, rank - base, 0, MPI_COMM_WORLD);
+      }
     }
     send += recv;
     base *= 2;
   }
+  base /= 2;
+  for (int i = 0; i < steps; ++i) {
+    if (rank % base == 0) {
+      int b = base * 2;
+      if (rank % b == 0) { // recv
+        MPI_Send(&send, 1, MPI_INT, rank + base, 0, MPI_COMM_WORLD);
+      } else { // send
+        MPI_Recv(&send, 1, MPI_INT, rank - base, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
+      }
+    }
+    base /= 2;
+  }
   // print result
   std::cout << "rank:" << rank << ", sum:" << send << std::endl;
   MPI_Finalize();