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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Possible compiler bug with this simple program
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Date: Fri, 29 Aug 2008 22:39:56 +0200
Message-ID: <87y72fr1wj.fsf@ludovic-brenta.org>
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Date: 2008-08-29T22:39:56+02:00
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Jerry writes:
> On Aug 28, 12:56 am, Ludovic Brenta <ludo...@ludovic-brenta.org>
> wrote:
>> I cannot test your program now but it seems to me that perhaps you
>> should specify the alignment of the arrays and Long_Floats. Also, it
>> might be a good idea to double-check that on the Intel Core 2, the
>> long floats are really 64 bits and not 80 bits wide. It could be that
>> the compiler got that wrong but I doubt it.
>>
> And that would look something like this?
>
> for Long_Float'Alignment use 64;
> for Real_Vector'Alignment use ???;

Yes.  In addition, these might help:

for Real_Vector'Component_Size use 64;
for Real_Vector'Alignment use 64;
pragma Pack (Real_Vector);

I'm actually puzzled as to why the program appears to work on 32-bit
platforms. I would expect a Storage_Error when accessing X (0) since,
per your declaration, X'First = Integer'First = -2**31, so X (0) is
probably way past the end of the array.  The first thing I would try
is using Natural instead of Integer as the array index subtype.  If
that fails, try specifying the 'Alignment and 'Component_Size.  If
that still fails, look at the assembly code emitted on amd64.

I just received http://bugs.debian.org/497067, BTW.

-- 
Ludovic Brenta.