From: Stefan Monnier <monnier@iro.umontreal.ca>
To: help-gnu-emacs@gnu.org
Subject: Re: (- 2.8 1.6) ; 1.1999999999999997
Date: Mon, 10 Feb 2020 20:31:56 -0500 [thread overview]
Message-ID: <jwvftfhrk7b.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: 8736biywcn.fsf@ebih.ebihd
> (- 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.
Stefan
next prev parent reply other threads:[~2020-02-11 1:31 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 [this message]
2020-02-11 1:50 ` Alexandre François Garreau
2020-02-11 1:55 ` Emanuel Berg via Users list for the GNU Emacs text editor
2020-04-07 14:00 ` Bruno Félix Rezende Ribeiro
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