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From: "Randy Brukardt" <randy@rrsoftware.com>
Subject: Re: What is the warning about builtin-function on gcc-4.6.0 ?
Date: Sat, 26 Mar 2011 21:08:56 -0500
Date: 2011-03-26T21:08:56-05:00	[thread overview]
Message-ID: <imm67s$49s$1@munin.nbi.dk> (raw)
In-Reply-To: 8762r5hl2u.fsf@mid.deneb.enyo.de

"Florian Weimer" <fw@deneb.enyo.de> wrote in message 
news:8762r5hl2u.fsf@mid.deneb.enyo.de...
...
>> If the compiler doesn't raise an exception on division by zero (it's
>> allowed not to, and GNAT doesn't) it will (in this case) set the result
>> to +Inf, and 'Valid will return False.
>
> My understanding is that an implementation must either raise
> Constraint_Error, or the evaluation of an expression must result in a
> valid value.

Your understanding is wrong.

The only real requirement on Ada math is that the resulting values are not 
used in a way that causes erroneous execution (and there is even an explicit 
hole allowing that for Unchecked_Conversion). Otherwise, using/producing an 
"invalid value" is allowed in almost all contexts -- but it is a bounded 
error so a compiler can raise an exception if it wants.

Also note that "abnormal" is something different from "invalid" (only scalar 
objects can be invalid).

Data validity is a very complex subject; you can read 13.9.1 10 times and 
get different impressions each time. Reading the e-mail on the various AIs 
on the topic (AI05-0195-1 is the most recent) and the AARM *might* help --  
or might confuse further. On top of that, different implementations use 
different models to ensure validity without inserting more checks than 
necessary.

                                            Randy.





  parent reply	other threads:[~2011-03-27  2:08 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-03-26  6:32 What is the warning about builtin-function on gcc-4.6.0 ? ytomino
2011-03-26  8:45 ` Florian Weimer
2011-03-26  9:13   ` ytomino
2011-03-26  9:43     ` Florian Weimer
2011-03-26 10:07       ` ytomino
2011-03-26 10:24         ` Florian Weimer
2011-03-26 15:14           ` Dmitry A. Kazakov
2011-03-26 21:36             ` ytomino
2011-03-27  9:50               ` Dmitry A. Kazakov
2011-03-26 14:50         ` Simon Wright
2011-03-26 15:50           ` Florian Weimer
2011-03-26 16:32             ` Simon Wright
2011-03-26 17:02               ` Florian Weimer
2011-03-26 17:48                 ` Simon Wright
2011-03-26 18:48                   ` Florian Weimer
2011-03-27  2:08                 ` Randy Brukardt [this message]
2011-03-27  8:37                   ` Florian Weimer
2011-03-27 16:41                     ` Robert A Duff
2011-03-27 17:21                       ` Florian Weimer
2011-03-27 17:56                         ` Robert A Duff
2011-03-27 16:51                     ` Robert A Duff
2011-03-27 17:05                       ` Florian Weimer
2011-03-27 17:14                         ` Robert A Duff
2011-03-29  2:20                           ` Randy Brukardt
2011-03-29 18:35                             ` Robert A Duff
2011-03-29 23:35                               ` Randy Brukardt
2011-03-30  1:02                               ` Adam Beneschan
2011-03-30 12:57                                 ` Robert A Duff
2011-03-30 14:41                                   ` Adam Beneschan
2011-03-30 18:39                                     ` Robert A Duff
2011-03-30 19:28                                   ` Randy Brukardt
2011-03-26 21:58       ` ytomino
2011-03-26 22:00         ` Florian Weimer
2011-03-26 22:22 ` anon
2011-03-26 22:36   ` ytomino
2011-03-27 12:00     ` anon
2011-03-27 18:50       ` ytomino
2011-03-27 23:35         ` anon
2011-03-27 23:42         ` anon
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