From: Jan Hubicka <jh@suse.cz>
To: Gabriel Dos Reis <gdr@integrable-solutions.net>
Cc: Andreas Schwab <schwab@suse.de>, Jan Hubicka <jh@suse.cz>,
gcc-patches@gcc.gnu.org
Subject: Re: Converting floor to rint
Date: Thu, 07 Nov 2002 07:01:00 -0000 [thread overview]
Message-ID: <20021107150055.GC11315@atrey.karlin.mff.cuni.cz> (raw)
In-Reply-To: <m3y985tq4g.fsf@soliton.integrable-solutions.net>
> Andreas Schwab <schwab@suse.de> writes:
>
> | Gabriel Dos Reis <gdr@integrable-solutions.net> writes:
> |
> | |> "may" part refers to the fact whether the programmer might want
> | |> to run rint() under a particular floating-point control mode that
> | |> would permit rint() to raise the inexact exception.
> | |> rint() cannot unconditionally set it. If FENV_ACCESS is on and
> | |> FE_INEXACT is supported then rint() should raise the exception if
> | |> appropriate. That is my understanding.
> |
> | If the implementation defines __STDC_IEC_559__ then F.9.6.4 applies. I
> | have no copy of IEC 60559, but if it states that rint must raise the
> | exception then it must do it independent of FENV_ACCESS.
Yes, IEC seems to be clear about the trap:
[#1] The rint functions differ from the nearbyint functions
only in that they do raise the ``inexact'' floating-point
exception if the result differs in value from the argument.
I would love to be enlightened about when this feature is usefull :) I
can't think of any use for it. Sadly most people use rint/lrint and not
nearbyint/lrint that are more consistent.
>
> My concern is this:
>
> F.7.1 Environment management
>
> [#1] IEC 60559 requires that floating-point operations
> implicitly raise floating-point exception status flags, and
> that rounding control modes can be set explicitly to affect
> result values of floating-point operations. When the state
> for the FENV_ACCESS pragma (defined in <fenv.h>) is ``on'',
> these changes to the floating-point state are treated as
> *side effects* which respect sequence points.304)
>
> (my emphasis)
So one can not consider rint as "attribute((const))" function and we can
not do that in strict mode.
>
> | Otherwise, if
> | __STDC_IEC_559__ is not defined, then no requirements on the exceptions
> | are stated for rint, since 7.12.9.4 does not have a "shall".
Can I detect somehow the cases when __STDC_IEC_559__ is not defined?
This seems to be done by glibc in all cases, even with -ffast-math.
Perhaps I can do the rint folding only with -ffast-math that would be
enought for majority of 3D software that is about the only case where we
get some oppurtunities for speedup from this transformations?
Honza
>
> Agreed.
>
> -- Gaby
next prev parent reply other threads:[~2002-11-07 15:01 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
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 [this message]
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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