zsh-workers
 help / color / mirror / code / Atom feed
From: Vincent Lefevre <vincent@vinc17.net>
To: zsh-workers@zsh.org
Subject: Re: zsh converts a floating-point number to string with too much precision
Date: Sat, 21 Dec 2019 02:00:18 +0100	[thread overview]
Message-ID: <20191221010018.GC767822@zira.vinc17.org> (raw)
In-Reply-To: <20191220165824.ufvjtx37xt7dp2dt@chaz.gmail.com>

On 2019-12-20 16:58:24 +0000, Stephane Chazelas wrote:
> https://unix.stackexchange.com/questions/422122/why-does-0-1-expand-to-0-10000000000000001-in-zsh
> 
> Reproduced below for convenience:
> 
> ════════════════════════════════════════════════════════════════
> 
> TL;DR
> 
> zsh chooses a decimal representation for the double binary
> numbers that it uses for evaluating floating point arithmetics
> that preserves their information fully, that is safe for reinput
> into its arithmetic expressions.

But there are several possible decimal representations with this
requirement.

> And that is done at the expense
> of cosmetic. For that, it needs 17 significant digits, and make
> sure the expansion always includes a . or e so it's treated as
> float on reinput.

This is only one way to fulfill the requirement. Here, it was assumed
that the output precision is chosen independently from the argument
(it seems that zsh chooses printf "%.17g"). But it does not need to
be like that.

BTW, what zsh does is not documented.

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

      parent reply	other threads:[~2019-12-21  1:01 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-20  1:37 Vincent Lefevre
2019-12-20  3:38 ` Mikael Magnusson
2019-12-20 16:58 ` Stephane Chazelas
2019-12-20 17:12   ` Roman Perepelitsa
2019-12-21  0:50     ` Vincent Lefevre
2019-12-21  8:47       ` Stephane Chazelas
2019-12-21  9:43         ` Roman Perepelitsa
2019-12-21 17:56           ` Stephane Chazelas
2019-12-21 18:11             ` Stephane Chazelas
2019-12-21 18:20               ` Roman Perepelitsa
2019-12-21 21:28         ` Vincent Lefevre
2019-12-21  1:00   ` Vincent Lefevre [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191221010018.GC767822@zira.vinc17.org \
    --to=vincent@vinc17.net \
    --cc=zsh-workers@zsh.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this public inbox

	https://git.vuxu.org/mirror/zsh/

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).