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Subject: Re: [OMPI devel] MPI_REAL16
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-06-22 12:52:57


Given that I'll inevitably get the language wrong, can someone suggest
proper verbiage for this statement in the OMPI README:

- MPI_REAL16 and MPI_COMPLEX32 are only supported on platforms where a
   portable C datatype can be found that matches the Fortran type
   REAL*16, both in size and bit representation. The Intel v11
   compiler, for example, supports these types, but requires the use of
   the "_16" suffix in Fortran when assigning constants to REAL*16
   variables.

Thanks!

On Jun 22, 2009, at 12:34 PM, N.M. Maclaren wrote:

> On Jun 22 2009, Iain Bason wrote:
> >Jeff Squyres wrote:
> >
> >> Thanks for looking into this, David.
> >>
> >> So if I understand that correctly, it means you have to assign all
> >> literals in your fortran program with a "_16" suffix. I don't
> know if
> >> that's standard Fortran or not.
> >
> >Yes, it is.
>
> Sorry - no, it isn't. It's syntactically standard, but has an
> undefined
> meaning.
>
> KIND parameters are processor dependent, and do NOT mean the size in
> bytes,
> words or anything else. On a VAX or Alpha, and potentially on IBM
> and Intel
> systems in the future, you could have several different floating-
> point types
> of the same length. Currently, not all compilers use the same
> conventions,
> even on the same system.
>
> The correct way to do it is to have a module that defines a suitable
> parameter, include that module everywhere, and use that parameter. For
> example:
>
> MODULE double
> INTEGER, PARAMETER :: dp = SELECTED_REAL_KIND(12)
> END MODULE double
>
> Include 'USE double' at the start of every procedure and module, and
> then
> use 1.23_DP.
>
>
> Regards,
> Nick Maclaren,
> University of Cambridge Computing Service,
> New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
> Email: nmm1_at_[hidden]
> Tel.: +44 1223 334761 Fax: +44 1223 334679
>
>
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>

-- 
Jeff Squyres
Cisco Systems