From: Vincent Lefevre <vincent+gcc@vinc17.org>
To: "Joseph S. Myers" <joseph@codesourcery.com>
Cc: munroesj@us.ibm.com, libc-alpha@sourceware.org, gcc@gcc.gnu.org,
Geert Bosch <bosch@adacore.com>,
Christoph Lauter <christoph.lauter@lip6.fr>
Subject: Re: The state of glibc libm
Date: Mon, 26 Mar 2012 10:26:00 -0000 [thread overview]
Message-ID: <20120326102605.GD9025@xvii.vinc17.org> (raw)
In-Reply-To: <Pine.LNX.4.64.1203221625460.6335@digraph.polyomino.org.uk>
On 2012-03-22 16:29:00 +0000, Joseph S. Myers wrote:
> On Thu, 22 Mar 2012, Vincent Lefevre wrote:
> > For the same reason, if the user chose long double instead of
> > double, this may be because he wanted more precision than double.
>
> You mean range? IBM long double provides more precision, but not more
> range.
Well, precision and/or range. If double precision format is sufficient
for his application, the user can just choose the "double" type. So,
I don't think that it is useful to have long double = double.
Then concerning double-double vs quad (binary128) for the "long double"
type, I think that quad would be more useful, in particular because
it has been standardized and it is a true FP format. If need be (for
efficiency reasons), double-double could still be implemented using
the "double" type, via a library or ad-hoc code (that does something
more clever, taking the context into account). And the same code (with
just a change of the base type) could be reused to get a double-quad
(i.e. quad + quad) arithmetic, that can be useful to implement the
"long double" versions of the math functions (expl, and so on).
> > So, in the long term, the ABI should probably be changed to have
> > long double = quadruple precision (binary128).
>
> The ABI for Power Architecture changed away from quad precision to using
> IBM long double (the original SysV ABI for PowerPC used quad precision,
> the current ABI uses IBM long double)....
Perhaps they could change back to quad precision.
--
Vincent Lefèvre <vincent@vinc17.net> - Web: <http://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <http://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
next prev parent reply other threads:[~2012-03-26 10:26 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-29 18:21 Joseph S. Myers
2012-02-29 21:56 ` David Miller
2012-03-14 14:31 ` Vincent Lefevre
2012-03-14 14:40 ` Joseph S. Myers
2012-03-15 2:08 ` Vincent Lefevre
2012-03-15 18:23 ` James Cloos
2012-03-16 12:17 ` Steven Munroe
2012-03-22 16:11 ` Vincent Lefevre
2012-03-22 16:29 ` Joseph S. Myers
2012-03-26 10:26 ` Vincent Lefevre [this message]
2012-03-26 16:13 ` Steven Munroe
2012-03-27 13:01 ` Vincent Lefevre
2012-03-14 16:11 ` Jeff Law
2012-03-14 16:30 ` Joseph S. Myers
2012-03-14 17:08 ` Jeff Law
2012-03-14 20:37 ` Andi Kleen
2012-03-14 21:05 ` Joseph S. Myers
2012-03-14 21:47 ` Andi Kleen
2012-03-15 9:46 ` Richard Guenther
2012-03-15 14:18 ` Andi Kleen
2012-03-15 14:24 ` Richard Guenther
2012-03-14 21:57 ` David Miller
2012-03-14 20:52 ` Marc Glisse
2012-03-14 21:08 ` Joseph S. Myers
2012-03-28 15:18 ` Joseph S. Myers
[not found] <CAFULd4bg4Ctr_CUZAduBbkV+s6A_Y0cACNfuiE5iAYRtEeUoDg@mail.gmail.com>
2012-03-15 14:53 ` Uros Bizjak
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