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From: Warner BRUNS <Warner.Bruns@cern.ch>
Newsgroups: comp.lang.ada
Subject: Re: GNAT compiler switches and optimization
Date: Mon, 23 Oct 2006 14:33:37 +0200
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Date: 2006-10-23T14:33:37+02:00
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Damien Carbonne wrote:
> Jeffrey Creem a �crit :
>> Followup on the bug report.
>>
>> One of the comments asserted that the two programs were not equivilent 
>> though I am not yet 100% convinced that I believe it yet.
>>
> <snip>
>>
>>
>> Can someone that understands FORTRAN better make an argument about the 
>> "closeness" of this approach v.s. the other?
> 
> I've been following this thread for some times and I'm not a Fortran 
> Guru,however, IIRC, Fortran arrays and Ada arrays don't have the same 
> memory layout (Something like row major order and column major order).
> I've not compared programs of this thread with care, but I've the 
> feeling that this could change things.
> Some years ago, I had to mix Ada and Fortran, and I remember that we had 
> to invert loops order to obtain the same result.
> One would need to add 'pragma Convention (Fortran, Real_Matrix)' on Ada 
> side to obtain the same result, or to exchange loops.
> My knowledge of Fortran was limited to Fortran 77, and I don't know if 
> this is still valid with Fortran 95 or later.
> But if is still true, I would not consider the 2 programs as equivalent.
> 
> Regards
> 
> Damien Carbonne
> 

A problem with Ada is that the memory layout of a twodimensional
array is not specified in the Ada Standard.
If you want to have a uniform memory layout between different Ada compilers,
you have to specify that the memory layout should be like Fortran would do it.
Very odd.

    TYPE DefReal IS DIGITS 12;
    TYPE DefReal2D IS ARRAY(DefInt RANGE <>,
                            DefInt RANGE <>) OF DefReal;
    PRAGMA CONVENTION (Fortran, DefReal2D);

Warner