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Subject: Re: [OMPI devel] RFC: add support for large counts using derived datatypes
From: George Bosilca (bosilca_at_[hidden])
Date: 2013-07-16 17:11:26


On Jul 16, 2013, at 23:07 , "Jeff Squyres (jsquyres)" <jsquyres_at_[hidden]> wrote:

> On Jul 16, 2013, at 5:03 PM, George Bosilca <bosilca_at_[hidden]> wrote:
>
>>> 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.
>
> Datatypes are used in FILE_SET_VIEW.

Doesn't matter. There you don't create a datatype, you force one on the view you have of the file. I guess the forum was a little overzealous …

  George.

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