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Re: [Gcl-devel] Re: [Maxima] m68k gcl/maxima: Minor Floating point erro

From: Camm Maguire
Subject: Re: [Gcl-devel] Re: [Maxima] m68k gcl/maxima: Minor Floating point errors
Date: 19 Sep 2002 15:41:50 -0400


James Amundson <address@hidden> writes:

> On Thu, 2002-09-19 at 11:09, Richard Fateman wrote:
> > for i:1 thru 60 do print ([i,is (1.0d0=1.0d0+2^(-i))]);  double
> > for i:1 thru 60 do print ([i,is (1.0=1.0+2^(-i))]); single
> > 
> > for the first one, you should get i=22 for the first true.
> > for the second one, i=53 should be the first true.
> Ah ha. By that test, single precision float are being implemented as
> doubles by all three of GCL, Clisp and CMUCL under Linux.
> Camm, what do you get?

Indeed, I get 53 on both.  I'm giving Rick Younie's suggestion of
-ffloat-store a try.  Apparently, the m68k can keep more precision for
doubles than standard IEEE dictates.  

> > The way I debug lisp functions is first to make sure
> > the same answer happens when the code is interpreted rather
> > than compiled.  (if not, it is a compiler error!)
> > Then if they are the same, by using trace.  You can
> > trace the two different versions and see where they
> > give different answers.   Rarely I
> > insert in the lisp code  (break "id") or output statements
> > like (format t "~% location xx with values ~s ~s "  x y)
> > 
> > Which all brings to mind the possibility that suggestions
> > like this should be in a FAQ ... How do I debug lisp code
> > in Maxima.
> Yes. Absolutely. CY was going to start a Wiki. What happened to it?
> (I'll confess that I've never really used a Wiki, but I believe it is
> supposed to be a more flexible implementation of a FAQ.)

>From my lowly perspective as a C person, having a tool with the same
functionality as gdb for lisp, as is apparently the case as described
in Dr. Schelter's docs for dbl mode, but which I have been unable to
reproduce, would be *very* attractive for people new to the language.

Take care,

> --Jim

Camm Maguire                                            address@hidden
"The earth is but one country, and mankind its citizens."  --  Baha'u'llah

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