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Re: Second Draft "Unsafe fp optimizations" project description.
- To: dewar at gnat dot com
- Subject: Re: Second Draft "Unsafe fp optimizations" project description.
- From: Toon Moene <toon at moene dot indiv dot nluug dot nl>
- Date: Mon, 06 Aug 2001 22:26:08 +0200
- CC: gcc at gcc dot gnu dot org
- Organization: Moene Computational Physics, Maartensdijk, The Netherlands
- References: <20010805223208.F07E2F2B79@nile.gnat.com>
> <<Obviously, it is useless to talk about the ill effects of rearranging
> floating point expressions without having a solid reference. To simplify the
> analysis below, this project confines itself to the targets that support the
> IEEE-754 Standard, using the standard rounding mode for reference.
> Once again, the IEEE-754 standard has nothing whatsoever to say about
> evaluation of floating-point expressions in high level languages.
I don't quite understand the "again" - if you wrote it before, it
certainly didn't hit my mailbox ...
Then again :-) yes I know that the IEEE-754 has nothing to say about
evaluation of floating point expressions in high level languages. The
point is that *we* want to say something about the (differences between)
evaluations of expressions - so we better have a frame of reference.
E.g., if we want to say that optimization -fblah will cause overflow
when the inputs to the (transformed) expression are in the subset X of
all representable floating point numbers, we have to assume a model - my
suggestion is to use the IEEE-754 model.
Toon Moene - mailto:email@example.com - phoneto: +31 346 214290
Saturnushof 14, 3738 XG Maartensdijk, The Netherlands
Maintainer, GNU Fortran 77: http://gcc.gnu.org/onlinedocs/g77_news.html
Join GNU Fortran 95: http://g95.sourceforge.net/ (under construction)