Add New MPI_OP-> MPI_MAX

src/mpi.f90

@@ -16,6 +16,7 @@ module mpi
     integer, parameter :: MPI_COMM_WORLD = -1000
     real(8), parameter :: MPI_IN_PLACE = -1002
     integer, parameter :: MPI_SUM = -2300
+    integer, parameter :: MPI_MAX = -2301
     integer, parameter :: MPI_INFO_NULL = -2000
     integer, parameter :: MPI_STATUS_SIZE = 5
     integer :: MPI_STATUS_IGNORE = 0
@@ -123,10 +124,12 @@ module mpi
     contains
 
     integer(kind=MPI_HANDLE_KIND) function handle_mpi_op_f2c(op_f) result(c_op)
-        use mpi_c_bindings, only: c_mpi_op_f2c, c_mpi_sum
+        use mpi_c_bindings, only: c_mpi_op_f2c, c_mpi_sum, c_mpi_max
         integer, intent(in) :: op_f
         if (op_f == MPI_SUM) then
             c_op = c_mpi_sum
+        else if (op_f == MPI_MAX) then
+            c_op = c_MPI_MAX
         else
             c_op = c_mpi_op_f2c(op_f)
         end if

src/mpi_c_bindings.f90

@@ -17,6 +17,7 @@ module mpi_c_bindings
     integer(kind=MPI_HANDLE_KIND), bind(C, name="c_MPI_INT") :: c_mpi_int
     integer(kind=MPI_HANDLE_KIND), bind(C, name="c_MPI_COMM_WORLD") :: c_mpi_comm_world
     integer(kind=MPI_HANDLE_KIND), bind(C, name="c_MPI_SUM") :: c_mpi_sum
+    integer(kind=MPI_HANDLE_KIND), bind(C, name="c_MPI_MAX") :: c_mpi_max
 
     interface
 

src/mpi_constants.c

@@ -15,3 +15,5 @@ MPI_Datatype c_MPI_INT = MPI_INT;
 void* c_MPI_IN_PLACE = MPI_IN_PLACE;
 
 MPI_Op c_MPI_SUM = MPI_SUM;
+
+MPI_Op c_MPI_MAX = MPI_MAX;

tests/reduce_max_op_01.f90

@@ -0,0 +1,37 @@
+program reduce_max_1
+    use mpi
+    implicit none
+    integer :: ierr, rank, size, root
+    integer :: sendbuf, recvbuf
+    logical :: error
+
+    ! Initialize MPI
+    call MPI_Init(ierr)
+    call MPI_Comm_rank(MPI_COMM_WORLD, rank, ierr)
+    call MPI_Comm_size(MPI_COMM_WORLD, size, ierr)
+
+    ! Root process
+    root = 0
+
+    ! Each process sends its rank + 100 as input
+    sendbuf = rank + 100
+
+    ! Perform reduction with MPI_MAX
+    call MPI_Reduce(sendbuf, recvbuf, 1, MPI_INTEGER, MPI_MAX, root, MPI_COMM_WORLD, ierr)
+
+    ! Verify result on root
+    error = .false.
+    if (rank == root) then
+        if (recvbuf /= size - 1 + 100) then
+            print *, "Error: Expected max ", size - 1 + 100, ", got ", recvbuf
+            error = .true.
+        else
+            print *, "MPI_Reduce with MPI_MAX test passed: max = ", recvbuf
+        end if
+    end if
+
+    ! Clean up
+    call MPI_Finalize(ierr)
+
+    if (error) stop 1
+end program reduce_max_1