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[Gcl-devel] Re: [ 101603 ] numerical quirks

From: Camm Maguire
Subject: [Gcl-devel] Re: [ 101603 ] numerical quirks
Date: Sun, 08 Dec 2002 17:52:10 -0500
User-agent: WEMI/1.13.7 (Shimada) FLIM/1.13.2 (Kasanui) Emacs/20.7 (i386-debian-linux-gnu) MULE/4.0 (HANANOEN)

Greetings!  I'm forwarding your note to the address@hidden list to
solicit comments on what a compliant lisp system should do in the
instances you note.  They all fall under the general rubric of fixed
precision floating point arithmetic.  Is lisp supposed to be able to
handle arbitrary precision floating point?  Does any implementation do
this?  I heard rumors once that clisp used gmp for floats too.  From
my understanding of earlier threads, a lisp implementation is not
supposed to be able to recognize and return exact answers to special
floating point problems, e.g. cos(pi/2), sqrt(-1), etc.

Take care,

address@hidden writes:

> Support Request #101603, was updated on 2002-Dec-07 10:44
> You can respond by visiting: 
> http://savannah.gnu.org/support/?func=detailsupport&support_id=101603&group_id=879
> Category: None
> Status: Open
> Priority: 5
> Summary: numerical quirks
> By: janos, at janos.ca
> Date: 2002-Dec-07 10:44
> Logged In: NO 
> Browser: Mozilla/5.0 Galeon/1.2.7 (X11; Linux i686; U;) Gecko/20021204 
> Debian/1.2.7-1
> This is actually a bug report, but your project seems
> to have the bug tracking tool turned off, so I'll write
> it here. Lisp is good at handling numbers. Accordingly,
> gcl can handle arbitrarily large integers. Thus, (expt
> 2 (expt 2 (expt 2 (expt 2 2)))) works. However, if you
> try subtracting 0.5 from it, gcl declares that the
> result is a non-number. I can understand limited
> floating-point precision, but its range should be
> unbounded, especially when integers are handled so
> well. Specifically, the internal variable in floats
> indicating order of magnitude should use just these
> unbounded integers.
> Second of all, why is (sqrt -1)
> #C(6.1230317691118863E-17 1.0)? I'm using gcl from
> Debian sid, version 2.5.0.cvs20020625-70.
> ----------------------------------------------------------------------
> You can respond by visiting: 
> http://savannah.gnu.org/support/?func=detailsupport&support_id=101603&group_id=879

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

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