From: Joern Rennecke <amylaar@cygnus.co.uk>
To: law@cygnus.com
Cc: jbuck@Synopsys.COM, moshier@mediaone.net,
tim@wagner.Princeton.EDU, tprince@cat.e-mail.com, bosch@gnat.com,
burley@gnu.org, egcs@cygnus.com, hjstein@bfr.co.il
Subject: Re: /internet
Date: Wed, 16 Dec 1998 17:52:00 -0000 [thread overview]
Message-ID: <199812170152.BAA27992@phal.cygnus.co.uk> (raw)
In-Reply-To: <28398.913854887@hurl.cygnus.com>
> The rules for FP are different becuase it's not 100% certain that the
> results after reassociation will be the same as before reassociation. Though
> I believe in the case reassociating a series of multiplies we are safe.
Only if the exponent freely overflows and underflows. However, often you'll
get Inf for an overflow and 0 for an underflow.
And if you come close to an underflow, you might get de-normalized numbers.
> Again, I have no intention of reassociating a + 5 + b + c for FP because of
> overflow concerns. The same restrictions are not necessary for multiplies
> though as far as I can tell.
>
> I challenge anyone to come up with a case where a reassociation of
> a * b * c * d produces different results than ((a * b) * c) * d.
(DBL_MAX * (DBL_MIN * DBL_MIN)) * 4 is different from
((DBL_MAX * DBL_MIN) * DBL_MIN) * 4
next prev parent reply other threads:[~1998-12-16 17:52 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
1998-12-15 15:06 /internet tprince
1998-12-15 19:12 ` /internet Stephen L Moshier
1998-12-15 19:21 ` /internet Joe Buck
1998-12-15 19:37 ` /internet Jeffrey A Law
1998-12-16 7:58 ` /internet Tim Hollebeek
1998-12-16 8:41 ` /internet Joe Buck
1998-12-16 11:45 ` /internet Stephen L Moshier
1998-12-16 11:59 ` /internet Joe Buck
1998-12-16 13:19 ` /internet Chip Salzenberg
1998-12-16 16:20 ` /internet Jeffrey A Law
1998-12-16 17:42 ` /internet Joern Rennecke
1998-12-17 9:46 ` /internet Horst von Brand
1998-12-16 16:37 ` /internet Jeffrey A Law
1998-12-16 16:56 ` /internet Per Bothner
1998-12-17 20:20 ` /internet Jeffrey A Law
1998-12-16 17:52 ` Joern Rennecke [this message]
1998-12-17 4:43 ` /internet Sylvain Pion
1998-12-17 10:26 ` /internet Craig Burley
1998-12-15 23:08 ` /internet Matthias Urlichs
1998-12-16 9:33 ` /internet Craig Burley
1998-12-16 5:44 ` /internet Stephen L Moshier
1998-12-16 9:37 ` /internet Craig Burley
-- strict thread matches above, loose matches on Subject: below --
1998-12-16 12:34 /internet Geert Bosch
1998-12-16 13:02 ` /internet Harvey J. Stein
1998-12-16 16:25 ` /internet Jeffrey A Law
1998-12-04 17:41 /internet tprince
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