Re: Second Draft "Unsafe fp optimizations" project description.

[Toon Moene <toon at moene dot indiv dot nluug dot nl>]

dewar@gnat.com wrote:

> <<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:toon@moene.indiv.nluug.nl - phoneto: +31 346 214290
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