GNU bug report logs - #6640
23.2; Why is this regexp search taking so long? (and will it end?)

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From: Ryan Rix <ryan <at> whatthefuck.computer>
To: 6640 <at> debbugs.gnu.org
Cc: michael <at> cadilhac.name
Subject: bug#6640: 23.2; Why is this regexp search taking so long? (and will it end?)
Date: Sun, 06 Mar 2016 04:12:59 +0000

michael <at> cadilhac.name "(Michaël" Cadilhac) writes:
> - emacs -Q
> - Clear the scratch buffer, and paste:
>
[redact]
>
> (a small input would give quite the same result).
> - M-< C-- C-s ^\([^:]*:[^:]*\)\{9\}
>
>   (everything works fine till now)
>
> add an $ to the regexp.
>
> - FEAR the possible endless loop (and the actual unexpected result of
>   taking long time).
>
> With an 8 in place of the 9, it takes a long time, but not possibly
> endless.
>
> Thanks!

Hi Michael,

Thanks for reporting this. I can confirm this is still an issue in the
latest emacs-25, commit e51b27ec2ce214ef3d8377a27ee9d857bcc66afc

I will leave it to smarter minds than my own to debug the regex engine,
though.

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