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Re: [PPL-devel] More floating point problems on the Alpha
- From: "Joseph S. Myers" <joseph at codesourcery dot com>
- To: Joe Buck <Joe dot Buck at synopsys dot COM>
- Cc: Abramo Bagnara <abramobagnara at tin dot it>, Roberto Bagnara <bagnara at cs dot unipr dot it>, gcc at gcc dot gnu dot org, The Parma Polyhedra Library developers' list <ppl-devel at cs dot unipr dot it>
- Date: Mon, 22 Sep 2008 21:41:05 +0000 (UTC)
- Subject: Re: [PPL-devel] More floating point problems on the Alpha
- References: <48D7DBAE.6000704@cs.unipr.it> <48D7F86E.1080106@tin.it> <20080922205021.GJ21866@synopsys.com>
On Mon, 22 Sep 2008, Joe Buck wrote:
> On Mon, Sep 22, 2008 at 09:56:30PM +0200, Abramo Bagnara wrote:
> > The problem come from the fact that for astonishing reasons 1.4e-45f is
> > not seen as 1.4e-45.
>
> Why is this astonishing? The smallest positive single-precision IEEE
> floating point number is roughly 1.175494e-38. Since user-specified
> numbers are rounded to the closest representable value, 1.4e-45f is
> a fancy way of typing zero.
The smallest subnormal value is approximately 1.40129846e-45F
(__FLT_DENORM_MIN__). The obvious conclusion is that subnormal support is
broken or disabled on Alpha by default.
--
Joseph S. Myers
joseph@codesourcery.com