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Re: Floating point problems (accuracy).
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: Vincent Lefevre <vincent+gcc at vinc17 dot org>
- Cc: James E Wilson <wilson at specifixinc dot com>, Phil Prentice <philp dot cheer at btinternet dot com>, mike at stec dot clara dot co dot uk, gcc-help at gcc dot gnu dot org, gcc at gcc dot gnu dot org
- Date: Wed, 9 Feb 2005 18:50:56 +0000 (UTC)
- Subject: Re: Floating point problems (accuracy).
- References: <E1Cqyvy-00085r-Ad@monty-python.gnu.org> <41ED7E6E.5080905@specifixinc.com><20050209161615.GA3300@dixsept.loria.fr>
On Wed, 9 Feb 2005, Vincent Lefevre wrote:
> There are no reasons not to fix it. For those who fear a performance
The x86 back-end needs changing so it no longer pretends that x87 floating
point operates other than on "long double". The front ends need to model
excess precision explicitly so that they can handle an expression of type
"double" being represented as long double and a cast from double to double
removing excess precision; even -ffloat-store only deals with assignment,
not casts, and I don't know whether precision will be discarded properly
by function call and return either. Then the front ends need some way of
representing the present vague semantics for -ffast-math when
down-conversions to double on assignment aren't required.
--
Joseph S. Myers http://www.srcf.ucam.org/~jsm28/gcc/
jsm@polyomino.org.uk (personal mail)
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