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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: Ada and Java. different behaviour. casting long to int problem.
Date: 1999/06/12
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 <FD7nFF.6D@stuyts.nl>
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In article <FD7nFF.6D@stuyts.nl>,
  jerry@jvdsys.stuyts.nl wrote:
> nabbasi@pacbell.net.NOSPAM wrote:
>
> The super-secret GNAT documentation will tell you that this is
> a very
> expensive check to perform, so it is by default disabled.

The very here is Jerry's invention :-)

The actual quote from the documentation is:

  We treat integer overflow specially
  because these are quite expensive and in our experience are
  not as important as other run-time checks in the development
  process.

and the "quite" here is probably right. We have in fact steadily
improved the quality of code for -gnato, so the penalty has been
reduced. It would be interesting to know what actual programs
see as a result of -gnato being off or on.

Note that the reason that overflow checking is rather different
from other checks is that it does not introduce safety issues.
You may get unexpected (e.g. modular wrapped) values, but you
don't get wild jumps, loads or stores as a result of overflow
checking being off.








> -- Jerry van Dijk | Leiden, Holland
> -- Team Ada       | jdijk@acm.org
> -- see http://stad.dsl.nl/~jvandyk
>


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