From: "Steve Doiel" <nospam_steved94@attbi.com>
Subject: Re: Valid on QNaN generates exception, compiler bug?
Date: Fri, 01 Feb 2002 22:13:58 GMT
Date: 2002-02-01T22:13:58+00:00 [thread overview]
Message-ID: <GqE68.834$S06.1959@rwcrnsc53> (raw)
In-Reply-To: 5ee5b646.0202011311.393ce8d9@posting.google.com
Thank you Robert.
I was hoping for a response from either you or Tuck (one I can trust).
SteveD
"Robert Dewar" <dewar@gnat.com> wrote in message
news:5ee5b646.0202011311.393ce8d9@posting.google.com...
> "Steve Doiel" <nospam_steved94@attbi.com> wrote in message
news:<cYx68.6829$IZ4.21489@rwcrnsc54>...
> > Interesting. I expected float_value'Valid to return
> > false, not raise an
> > exception.
>
> And of course your expectation was entirely correct. This
> is a clear bug (some earlier version of GNAT had this bug,
> and for a while we actually installed an implicit exception
> handler to catch the bogus exception and return False, but
> now GNAT does explicit code to test for and catch NaN's
> and infinities. The problem is that a signalling NaN may
> raise an exception just by loading it.
>
> But the prefix of 'Valid is very special. As we read in
> 13.9.2, the ONLY way you can use an invalid value like
> a NaN is in this context:
>
> 12 (20) X'Valid is not considered to be a read of X;
> hence, it is not an
> error to check the validity of invalid data.
>
> There is no basis whatsoever for raising a Constraint_Error
> here, the program is correct, and the 'Valid attribute
> should yield False. Report the bug to the relevant vendor.
>
> You definitely do NOT need to guard all 'Valid attributes
> with an exception handler (which is what the previous
> incorrect response would have implied).
next prev parent reply other threads:[~2002-02-01 22:13 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-01-31 4:04 Valid on QNaN generates exception, compiler bug? Steve Doiel
2002-02-01 14:12 ` Stephen Leake
2002-02-01 14:51 ` Steve Doiel
2002-02-01 21:11 ` Robert Dewar
2002-02-01 22:13 ` Steve Doiel [this message]
2002-02-01 16:16 ` Jeffrey Carter
-- strict thread matches above, loose matches on Subject: below --
2002-01-31 4:04 Steve Doiel
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