io/ompio: possible rounding issue

Similar to #6286 rounding number of bytes into a single precision floating point value to round up the result of a division is a potential risk due to rounding errors.

- remove floating point operations for `round up`
- removes floating point conversion for round down (native behavior of integer division)

Signed-off-by: René Widera <[email protected]>

Note: a direct cherry pick of commit a91fab8 is not possible, due to structural differences between the the 3.1.x and the master/v4.0.x branch. This commit is the equivalent of commit  a91fab8.

Signed-off-by: Edgar Gabriel <[email protected]>

Author: edgargabriel

ompi/mca/io/ompio/io_ompio_aggregators.c

@@ -738,11 +738,12 @@ int mca_io_ompio_split_initial_groups(mca_io_ompio_file_t *fh,
     int size_smallest_group = 0;
     int num_groups = 0;
     int ret = OMPI_SUCCESS;
-
+    
     OMPI_MPI_OFFSET_TYPE max_cci = 0;
     OMPI_MPI_OFFSET_TYPE min_cci = 0;
 
-    size_new_group = ceil ((float)mca_io_ompio_bytes_per_agg * fh->f_init_procs_per_group/ bytes_per_group);
+    // integer round up
+    size_new_group = (int)(mca_io_ompio_bytes_per_agg / bytes_per_group + (mca_io_ompio_bytes_per_agg % bytes_per_group ? 1u : 0u));
     size_old_group = fh->f_init_procs_per_group;
 
     ret = mca_io_ompio_split_a_group(fh,
@@ -790,7 +791,7 @@ int mca_io_ompio_split_initial_groups(mca_io_ompio_file_t *fh,
 		 if((max_cci < OMPIO_CONTG_THRESHOLD) &&
 		    (size_new_group < size_old_group)){
 
-		    size_new_group = floor( (float) (size_new_group + size_old_group ) / 2 );
+                    size_new_group = (size_new_group + size_old_group ) / 2;
   	            ret = mca_io_ompio_split_a_group(fh,
                                                      start_offsets_lens,
                                                      end_offsets,
@@ -818,7 +819,9 @@ int mca_io_ompio_split_initial_groups(mca_io_ompio_file_t *fh,
 	            (size_new_group < size_old_group)){  //can be a better condition
                  //monitor the previous iteration
 		 //break if it has not changed.
-	      	     size_new_group = ceil( (float) (size_new_group + size_old_group ) / 2 );
+                     size_new_group = size_new_group + size_old_group;
+                     // integer round up
+                     size_new_group = size_new_group / 2 + (size_new_group % 2 ? 1 : 0);
 		     ret = mca_io_ompio_split_a_group(fh,
                                                       start_offsets_lens,
                                                       end_offsets,