From: Joseph Myers <joseph@codesourcery.com>
To: Tejas Joshi <tejasjoshi9673@gmail.com>
Cc: <gcc@gcc.gnu.org>, Martin Jambor <mjambor@suse.cz>, <hubicka@ucw.cz>
Subject: Re: [PATCH] Builtin function roundeven folding implementation
Date: Thu, 22 Aug 2019 16:35:00 -0000 [thread overview]
Message-ID: <alpine.DEB.2.21.1908221633440.29112@digraph.polyomino.org.uk> (raw)
In-Reply-To: <CACMrGjCUbFja_j_gUquQuAO=HKam9j-R5+-cjde+_eWsfDs+XA@mail.gmail.com>
On Thu, 22 Aug 2019, Tejas Joshi wrote:
> > I'm concerned that this would produce +0.0 for an argument of -0.5 (via
> > -0.5 - 0.5 - -1.0 producing +0.0) when it needs to produce -0.0.
>
> Would the following overhaul be acceptable as the condition is
> specialized for -0.5 and +0.5 only. This seems to solve the problem. I
> did test the roundeven tests and it passes the tests.
I think that would be reasonable with a comment added to explain that it's
ensuring the correct sign of a zero result.
> if (__builtin_copysign (1, __builtin_roundeven (-0.5)) != -1)
> link_error (__LINE__);
I think you should have at least four tests of sign of zero result
(arguments -0.5, -0.0, 0.0 and 0.5). Probably also tests of values
between +/- 0.5 and 0, e.g. test -0.25 and 0.25 as well.
--
Joseph S. Myers
joseph@codesourcery.com
next prev parent reply other threads:[~2019-08-22 16:35 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CACMrGjCu54zN+Smc7+3JF8MBZV76HXwaP-vk1HFTQGhRc=Toww@mail.gmail.com>
[not found] ` <alpine.DEB.2.21.1908092021090.31221@digraph.polyomino.org.uk>
[not found] ` <CACMrGjCPNr+Hjz--CL6ocV5y3GqGp13fpQCXtXJT4qeGQWk86A@mail.gmail.com>
[not found] ` <ri636hug2zr.fsf@suse.cz>
[not found] ` <alpine.DEB.2.21.1908211156360.6172@digraph.polyomino.org.uk>
[not found] ` <ri6pnkye7ll.fsf@suse.cz>
[not found] ` <alpine.DEB.2.21.1908211906340.25161@digraph.polyomino.org.uk>
[not found] ` <ri6ftlte12y.fsf@suse.cz>
[not found] ` <alpine.DEB.2.21.1908221426570.27000@digraph.polyomino.org.uk>
2019-08-22 16:28 ` Tejas Joshi
2019-08-22 16:35 ` Joseph Myers [this message]
2019-08-22 16:56 ` Tejas Joshi
2019-08-22 17:00 ` Joseph Myers
[not found] ` <CACMrGjA3UyUYcShruM-tiT=rqBiSLX9cmSVmpX0G6SfOq_r4EQ@mail.gmail.com>
[not found] ` <alpine.DEB.2.21.1908232023080.19272@digraph.polyomino.org.uk>
2019-08-25 8:25 ` Tejas Joshi
2019-08-25 9:38 ` Martin Jambor
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