When we advance the convertor by a multiple of the data size there is a quick optimization.

We can compute the number of complete datatype that we will advance, update the stack and
then compute the new position taking in acount only the remaining bytes.

This commit was SVN r8019.

ompi/datatype/new_position.c

@@ -115,6 +115,24 @@ int ompi_convertor_generic_simple_position( ompi_convertor_t* pConvertor,
     description = pConvertor->use_desc->desc;
 
     base_pointer = pConvertor->pBaseBuf;
+
+    /* We dont want to have to parse the datatype multiple times. What we are interested in
+     * here is to compute the number of completed datatypes that we can move forward, update
+     * the the counters and finally compute the position taking in account only the remaining
+     * elements. The only problem is that we have to modify all the elements on the stack.
+     */
+    iov_len_local = *position - pConvertor->bConverted;
+    if( iov_len_local > pConvertor->pDesc->size ) {
+        long extent = pConvertor->pDesc->ub - pConvertor->pDesc->lb;
+
+        count_desc = iov_len_local / pConvertor->pDesc->size;
+        for( type = 0; type <= pConvertor->stack_pos; type++ )
+            pConvertor->pStack[type].disp += extent;
+        pConvertor->bConverted += count_desc * pConvertor->pDesc->size;
+        iov_len_local = *position - pConvertor->bConverted;
+        pConvertor->pStack[0].count -= count_desc;
+    }
+
     pStack = pConvertor->pStack + pConvertor->stack_pos;
     pos_desc      = pStack->index;
     base_pointer += pStack->disp;
@@ -129,7 +147,6 @@ int ompi_convertor_generic_simple_position( ompi_convertor_t* pConvertor,
                            pos_desc, count_desc, base_pointer - pConvertor->pBaseBuf,
                            pConvertor->stack_pos, pStack->index, pStack->count, pStack->disp ); );
 
-    iov_len_local = *position;
     while( 1 ) {
         if( DT_END_LOOP == pElem->elem.common.type ) { /* end of the current loop */
             DO_DEBUG( opal_output( 0, "pack end_loop count %d stack_pos %d pos_desc %d disp %ld space %d\n",