Thank you Martin. Meanwhile, I fell in a rabbit hole (your fault guys!) and I produced this thing. I am sure it is code that has been written a godzillion times before. I will use it for the next phase of debugging.
Please poke holes into it. All the best Marco On Fri, Nov 10, 2023 at 2:45 PM Martin Simmons <mar...@lispworks.com> wrote: > 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-...@lispworks.com> wrote: > > > > > > > > > > > On 9 Nov 2023, at 21:21, Marco Antoniotti <marco.antonio...@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__ > > > > > > > > > > > > > > > > > > > _______________________________________________ > Lisp Hug - the mailing list for LispWorks users > lisp-...@lispworks.com > http://www.lispworks.com/support/lisp-hug.html >
float-formatting.lisp
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