On Jul 16, 2013, at 4:03 PM, George Bosilca <bosi...@icl.utk.edu> wrote:
> On Jul 16, 2013, at 22:29 , Jeff Squyres (jsquyres) <jsquy...@cisco.com> > wrote: > >> On Jul 16, 2013, at 4:22 PM, George Bosilca <bosi...@icl.utk.edu> wrote: >> >>> Btw, I have a question to you fellow MPI Forum attendees. I just can't >>> remember why the MPI forum felt there was a need for the >>> MPI_Type_get[_true]_extent_x? MPI_Count can't be bigger than MPI_Aint, >> >> Yes, it can -- it has to be the largest integer type (i.e., it even has to >> be able to handle an MPI_Offset). > > Technicalities! In the entire standard MPI_Offset is only used to access > files, not to build datatypes. As such there is no way to have the extent of > an datatype bigger than MPI_Aint. That's not true. You can obtain a datatype with an extent outside the range of an MPI_Aint by nesting types. Just create a contig of size 1, then create a type a very large extent from your contig with MPI_Type_create_resized, then create a second contig of that resized with a count >1. > Thus, these accessors returning MPI_Count are a useless overkill, as they > cannot offer more precision that what the version returning MPI_Aint is > already offering. > > George. > > PS: I hope nobody has the idea to define the MPI_Offset as a signed type … Not sure if you're joking here... MPI_Offset must also be signed, again, for Fortran interoperability. -Dave
