Actually, ULP is not the same on LispWorks, which is why it diverges at 14.
You can't see it when printing 20 decimal places.

The reason is that LispWorks calculates (expt 2.0d0 -52) using natural
logarithms, so loses a few bits of precision.  If you change it to use
(/ 1d0 (ash 1 30) (ash 1 22)) or (float (expt 2 -52) 1d0) then LispWorks also
appears to diverge at 21 like on other Lisps.

Looking at the binary representation of the floats shows that this divergence
at 21 is just in the printing.  The C library prints some extra digits that
are not needed.

--
Martin Simmons
LispWorks Ltd
http://www.lispworks.com/



>>>>> On Fri, 10 Nov 2023 09:55:38 +0100, Marco Antoniotti said:
>
> Hi
>
> Thanks Pascal.
>
> For LW on Intel (Mac) the ULP seems the same.  With SBCL you should
> actually be able to peek at the actual bits making up the double float.
> Can you do something similar with LM?
>
> Just curious: has anybody tried this on a M*/Arm Mac?  Or, with LW, on your
> smartphone? :)
>
> Cheers
>
> MA
>
>
> On Fri, Nov 10, 2023 at 8:29 AM Pascal Bourguignon (as pjb at informatimago
> dot com) <lisp-hug@lispworks.com> wrote:
>
> >
> >
> > On 9 Nov 2023, at 21:21, Marco Antoniotti <marco.antoniotti@unimib.it>
> > wrote:
> >
> > <problem-loop.lisp>
> >
> >
> >
> > From the start, it looks like the ulp is more precise in C:
> >
> >
> > sbcl:   2.220446049250313d-16
> > clang: 2.2204460492503130808e-16
> >
> > (using %.20g instead of %.20f)
> >
> > Or perhaps it’s only the display procedure that truncates in lisp?
> >
> > --
> > __Pascal J. Bourguignon__
> >
> >
> >
> >
> >
>

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