public inbox for libc-alpha@sourceware.org
 help / color / mirror / Atom feed
From: Florian Weimer <fweimer@redhat.com>
To: Paul Eggert <eggert@cs.ucla.edu>
Cc: Siddhesh Poyarekar <siddhesh@gotplt.org>,
	 GNU C Library <libc-alpha@sourceware.org>
Subject: Re: 'trusted and reasonably structured' regular expressions
Date: Wed, 24 Feb 2021 20:56:58 +0100	[thread overview]
Message-ID: <87czwpp7cl.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <48c174b0-3fd5-5c38-a70b-0ef288c84fcd@cs.ucla.edu> (Paul Eggert's message of "Wed, 24 Feb 2021 11:49:04 -0800")

* Paul Eggert:

> On 2/24/21 11:18 AM, Florian Weimer wrote:
>> POSIX Extended regexps are not NP-complete (if I understand these terms
>> correctly)
>
> Hmm, I thought they were. See, for example, Schmid's paper[1], which
> says "The matching problem of regex, i. e., deciding whether a given 
> regex can match a given word, is NP-complete (even for strongly
> restricted variants)". Schmid defines "regex" to mean regular 
> expressions with backreferences.

POSIX Basic regexps support backreferences, POSIX Extended regexps do
not.  So the terminology is kind of reversed there.

Thanks,
Florian


  reply	other threads:[~2021-02-24 19:56 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-24  4:53 Siddhesh Poyarekar
2021-02-24 18:16 ` Paul Eggert
2021-02-24 19:18   ` Florian Weimer
2021-02-24 19:49     ` Paul Eggert
2021-02-24 19:56       ` Florian Weimer [this message]
2021-02-24 22:37 ` Joseph Myers
2021-02-25  2:51   ` Siddhesh Poyarekar
2021-02-25  3:03     ` Zack Weinberg
2021-02-25  3:15       ` Siddhesh Poyarekar
2021-02-25  3:26         ` Zack Weinberg
2021-02-25  4:53         ` Paul Eggert
2021-02-25  5:27           ` Siddhesh Poyarekar
2021-02-26 21:12             ` Paul Eggert
2021-03-02 10:58               ` Siddhesh Poyarekar

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=87czwpp7cl.fsf@oldenburg.str.redhat.com \
    --to=fweimer@redhat.com \
    --cc=eggert@cs.ucla.edu \
    --cc=libc-alpha@sourceware.org \
    --cc=siddhesh@gotplt.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. 
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 read-only IMAP folder(s) and NNTP newsgroup(s).