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Re: x87 float truncation/accuracy (gcc vs. icc/msvc)

From: Jakub Jelinek <jakub at redhat dot com>
To: Thomas Kunert <kunert at physik dot tu-dresden dot de>
Cc: Roger Sayle <roger at eyesopen dot com>, gcc at gcc dot gnu dot org
Date: Fri, 19 Mar 2004 07:16:51 +0100
Subject: Re: x87 float truncation/accuracy (gcc vs. icc/msvc)
References: <Pine.LNX.4.44.0403180818300.16213-100000@www.eyesopen.com> <405AAC97.60308@physik.tu-dresden.de>
Reply-to: Jakub Jelinek <jakub at redhat dot com>

On Fri, Mar 19, 2004 at 09:17:27AM +0100, Thomas Kunert wrote:
> Roger Sayle wrote:
> 
> >interesting is that both the Microsoft Visual C/C++ compiler and Intel's
> >icc both *by default* completely optimized away this "float_truncate",
> >producing incorrectly rounded results.
> >
> 
> Could you please explain what's wrong with incorrectly rounded results?
> I was under the impression accuracy and performance is more important to
> most people. And for the ones who actually care about rounding
> there is -ffloat-store. What is this option for, if the truncation happens
> anyway?

OTOH ISO C99 requires certain handling of float/double which
GCC on IA-32 doesn't meet even with -ffloat-store.

	Jakub

References:
- x87 float truncation/accuracy (gcc vs. icc/msvc)
  - From: Roger Sayle
- Re: x87 float truncation/accuracy (gcc vs. icc/msvc)
  - From: Thomas Kunert

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