Subject: Re: accuracy of "long double"
To: Neil Booth <neil@daikokuya.co.uk>
From: Matthias Drochner <M.Drochner@fz-juelich.de>
List: tech-toolchain
Date: 08/21/2007 12:08:10
neil@daikokuya.co.uk said:
> I'm afraid I don't see your point; your code seems to support
> everything I said. 

So I've appearently mistaken what you said:

neil@daikokuya.co.uk said:
> d) Despite many claims to the contrary that you will read on the
>    net, and on GCC lists, there is no double-rounding problem.
>    All results are correctly rounded to 53-bits given the value
>    they operated on

I had read this as "gcc will emit code which makes sure that
double results are correctly rounded even if the FPU is in
extended precision mode".
My code was just to show that this is not the case.

So we can't have good "long double" support and correct
"double" arithmetics at the same time. (at least as long
as we have to deal with pre-SSE2 CPUs)

best regards
Matthias




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