From: Emanuel Berg via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>
To: help-gnu-emacs@gnu.org
Subject: Re: (- 2.8 1.6) ; 1.1999999999999997
Date: Tue, 11 Feb 2020 02:55:35 +0100 [thread overview]
Message-ID: <87eev1yjjc.fsf@ebih.ebihd> (raw)
In-Reply-To: jwvftfhrk7b.fsf-monnier+emacs@gnu.org
Stefan Monnier wrote:
>> (- 2.8 1.6) ; 1.1999999999999997
>
> Emacs Lisp, like most common programming
> language doesn't support rational numbers
> (and even less real numbers, which can't be
> faithfully represented in a computer) but
> only floating point numbers. And like most
> programming languages it uses the standard
> IEEE representation supported natively by
> most CPUs. This representation can't
> represent 2.8 nor 1.6 (and nor 1.2) exactly.
>
> It so happens that "the representable number
> closest to 2.8" minus "the representable
> number closest to 1.6" is not equal to "the
> representable number closest to 1.2".
>
>> With the TI-84 Plus,
>>
>> 2.8-1.6=1.2
>
> IIUC those calculators used a decimal
> floating point representation, which suffers
> from the same kinds of problems of course,
> but works better in this specific case.
Sure seems like it :)
--
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal
next prev parent reply other threads:[~2020-02-11 1:55 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-10 21:18 (- 2.8 1.6) ; 1.1999999999999997 Emanuel Berg via Users list for the GNU Emacs text editor
2020-02-10 21:31 ` tomas
2020-02-10 21:33 ` Joost Kremers
2020-02-10 23:10 ` Emanuel Berg via Users list for the GNU Emacs text editor
2020-02-11 1:31 ` Stefan Monnier
2020-02-11 1:50 ` Alexandre François Garreau
2020-02-11 1:55 ` Emanuel Berg via Users list for the GNU Emacs text editor [this message]
2020-04-07 14:00 ` Bruno Félix Rezende Ribeiro
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