[MPI3 Fortran] MPI_SIZEOF question

[Bill Long]

The difficulty in writing things like this in Fortran is why the 
standard provides intrinsics.  In this case, see STORAGE_SIZE, which 
returns the size of an array element of the type of the argument in 
bits.  Dividing by 8 and multiplying by the array size (if the argument 
is not a scalar) should be simple enough for the user.

On 5/23/11 8:30 AM, Jeff Squyres wrote:
> I'm re-working Open MPI's Fortran implementation with Craig.
>
> The MPI_SIZEOF function is supposed to return the size of any Fortran intrinsic data type.  MPI-2.2 16.2.5 p494:31-44 says:
>
> -----
> The following functions allow a user to obtain a size-specific MPI datatype for any intrinsic Fortran type.
>
> MPI_SIZEOF(x, size)
> IN x	a Fortran variable of numeric intrinsic type (choice)
> OUT size	size of machine representation of that type (integer)
>

This one is very close to STORAGE_SIZE.  Just divide by 8.

> MPI_SIZEOF(X, SIZE, IERROR)
> <type>  X
> INTEGER SIZE, IERROR
>

This one would require also multiplying by the size of an array 
argument.  I assume the IERROR is there only to provide a distinction 
for the generic interface.  It is hard to imagine an actual run-time 
error with a routine like this.

Ultimately, I'd be inclined to just scrap the routine as redundant.

Cheers,
Bill


> This function returns the size in bytes of the machine representation of the given variable. It is a generic Fortran routine and has a Fortran binding only.
> -----
>
> Is there any way of implementing that other than an interface with an overloaded subroutine for every single intrinsic type (including dimension)?
>

-- 
Bill Long                                           longb at cray.com
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