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From: Martin Krischik <krischik@users.sourceforge.net>
Newsgroups: comp.lang.ada
Subject: Re: volatile vs aliased
Date: Fri, 07 Oct 2005 08:36:32 +0200
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Date: 2005-10-07T08:36:32+02:00
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Bj�rn Persson wrote:

> Rolf wrote:
>> Do we have a difference to C/C++ increment operator here? consider
>> 
>> pragma Volatile (x);
>> x := x + 1;   -- (1)
>>         vs.
>> x++;          -- (2)
>> 
>> In the Ada case (1) we are forced to have "read from memory",
>> "increment" and "write to memory" instructions, whereas in C/C++ (2)
>> you can get a single "increment memory" instruction (presuming the
>> mentioned assembler instructions exist on a given processor)
> 
> Are there really memory chips with built-in arithmetic circuitry, so
> that the processor can send an "add one" instruction to the memory and
> have the variable incremented without reading it first? At least I've
> never heard of that. As far as I know, adding and subtracting is the
> processor's job.
> 
> And why would you use pragma Volatile on a variable stored in the
> memory, anyway? As Ludovic described it, it would only be useful on
> variables mapped to special hardware devices. I don't think you would
> want to store a counter there.

Or you have a multi tasking application with C interface.

Martin
-- 
mailto://krischik@users.sourceforge.net
Ada programming at: http://ada.krischik.com