From: Jan Hubicka <jh@suse.cz>
To: Richard Henderson <rth@redhat.com>, Jan Hubicka <jh@suse.cz>,
Gabriel Dos Reis <gdr@integrable-solutions.net>,
gcc-patches@gcc.gnu.org, aj@suse.de
Subject: Re: Converting floor to rint
Date: Wed, 06 Nov 2002 14:53:00 -0000 [thread overview]
Message-ID: <20021106225353.GI1316@atrey.karlin.mff.cuni.cz> (raw)
In-Reply-To: <20021106224721.GK22215@redhat.com>
> On Wed, Nov 06, 2002 at 11:29:22PM +0100, Jan Hubicka wrote:
> > On the related note. How bad would you consider converting
> > floor(x) into rint(x-0.5) in the fast-math mode?
>
> Well, let's see...
>
> If the current rounding mode is FE_UPWARD, then
>
> rint(1.7 - 0.5) = rint(1.2) = 2.0
>
> I.e. we'd be computing CEIL instead of FLOOR.
>
> If the current rounding mode is FE_TONEAREST, which is the case
> I assume you were thinking about, we round ties to even, so
>
> rint(5.0 - 0.5) = rint(4.5) = 4.0
>
> instead of the expected value 5.0.
>
> So, I think this would be a very bad idea, even for -ffast-math.
Hmmm... OK then :(
Honza
>
>
>
> r~
next prev parent reply other threads:[~2002-11-06 22:53 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-11-05 9:14 Simplify floating point conversions Jan Hubicka
2002-11-05 9:38 ` Richard Henderson
2002-11-05 9:42 ` Jan Hubicka
2002-11-06 1:23 ` Simplify floating point conversions II Jan Hubicka
2002-11-06 3:08 ` Michael Matz
2002-11-06 4:36 ` Jan Hubicka
2002-11-06 9:54 ` Jan Hubicka
2002-11-06 10:09 ` Richard Henderson
2002-11-06 13:11 ` Jan Hubicka
2002-11-06 13:19 ` Jan Hubicka
2002-11-06 13:35 ` Gabriel Dos Reis
2002-11-06 13:36 ` Jan Hubicka
2002-11-06 14:06 ` Gabriel Dos Reis
2002-11-06 14:29 ` Converting floor to rint Jan Hubicka
2002-11-06 14:47 ` Richard Henderson
2002-11-06 14:53 ` Jan Hubicka [this message]
2002-11-06 14:55 ` Gabriel Dos Reis
2002-11-07 1:21 ` Jan Hubicka
2002-11-07 1:32 ` Jakub Jelinek
2002-11-07 1:33 ` Gabriel Dos Reis
2002-11-07 1:44 ` Jan Hubicka
2002-11-07 1:52 ` Jakub Jelinek
2002-11-07 1:54 ` Jan Hubicka
2002-11-07 2:04 ` Jan Hubicka
2002-11-07 4:47 ` Gabriel Dos Reis
2002-11-07 4:56 ` Jan Hubicka
2002-11-07 5:14 ` Andreas Schwab
2002-11-07 5:27 ` Gabriel Dos Reis
2002-11-07 5:31 ` Jan Hubicka
2002-11-07 5:35 ` Andreas Schwab
2002-11-07 5:22 ` Gabriel Dos Reis
2002-11-07 5:43 ` Andreas Schwab
2002-11-07 6:23 ` Gabriel Dos Reis
2002-11-07 7:01 ` Jan Hubicka
2002-11-07 7:18 ` Gabriel Dos Reis
2002-11-06 13:48 ` Simplify floating point conversions III Jan Hubicka
2002-11-06 14:55 ` Richard Henderson
2002-11-07 2:54 ` Simplify floating point conversions IV Jan Hubicka
2002-11-18 15:01 ` Richard Henderson
2002-11-05 11:14 ` Simplify floating point conversions Geoff Keating
2002-11-06 1:09 ` Jan Hubicka
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