From: Joe Buck <Joe.Buck@synopsys.COM>
To: Robert Dewar <dewar@gnat.com>
Cc: gcc@gcc.gnu.org
Subject: Re: -ffast-math and floating point reordering
Date: Fri, 26 Mar 2004 20:18:00 -0000 [thread overview]
Message-ID: <20040326103340.A5416@synopsys.com> (raw)
In-Reply-To: <406474D6.7090705@gnat.com>; from dewar@gnat.com on Fri, Mar 26, 2004 at 01:22:14PM -0500
On Fri, Mar 26, 2004 at 01:22:14PM -0500, Robert Dewar wrote:
> Joe Buck wrote:
> > On Thu, Mar 25, 2004 at 01:03:39AM -0500, Robert Dewar wrote:
> > What is "model interval"?
>
> Brief answer (long answer is too long). When the result of an
> fpt operation is exactly representable, the model interval is
> the set consisting of this one number.
>
> When the result is not exactly representable, then the model
> interval is the range of results between the two representable
> values surrounding the true real result, including the end
> points.
>
> Generally any value within the model interval can be returned,
> either end point, or, using temporary excess precision, some
> value in between.
>
> An optimization like reassociation is permitted only if the
> result is within the model interval of the original result
> as defined by the canonical semantics.
Thanks for the explanation. This appears to be just a hair looser than
C99 with __STDC_IEC_599__, because with IEEE floating point the rounding
direction is specified, and this suggests that Ada allows any operation to
round in either direction.
However, I doubt that there are any associative-operator rearrangements
that are permitted by this rule in Ada but not permitted in C (given that
the as-if rule permits any transformation that does not change the
result).
next prev parent reply other threads:[~2004-03-26 18:33 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-03-25 6:03 Joe Buck
2004-03-25 6:05 ` Ian Lance Taylor
2004-03-25 11:27 ` Robert Dewar
2004-03-25 11:31 ` Ian Lance Taylor
2004-03-25 11:55 ` Ben Elliston
2004-03-25 12:37 ` Robert Dewar
2004-03-25 10:22 ` Robert Dewar
2004-03-25 18:28 ` Joe Buck
2004-03-25 18:38 ` Dave Korn
2004-03-26 20:06 ` Robert Dewar
2004-03-26 20:18 ` Joe Buck [this message]
2004-03-25 16:12 ` Paul Koning
2004-03-25 18:46 ` Dale Johannesen
2004-03-25 20:11 ` Geert Bosch
2004-03-27 1:51 ` Robert Dewar
2004-03-27 2:39 ` Dale Johannesen
2004-03-26 18:18 ` law
2004-03-26 18:37 ` Joe Buck
2004-03-26 18:46 ` Diego Novillo
2004-03-26 19:03 ` Richard Guenther
2004-03-26 19:54 ` Fariborz Jahanian
2004-03-26 20:19 ` law
2004-03-26 22:08 ` Joe Buck
2004-03-27 0:42 ` Richard Henderson
2004-03-26 22:12 ` Joseph S. Myers
2004-03-26 21:48 ` Laurent GUERBY
2004-03-26 11:20 Bradley Lucier
2004-03-26 18:33 Robert Dewar
2004-03-26 22:22 Chris Lattner
2004-03-26 22:27 ` Chris Lattner
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