From: Andreas Schwab <schwab@linux-m68k.org>
To: Leo Liu <sdl.web@gmail.com>
Cc: emacs-devel@gnu.org
Subject: Re: why is reverse a string in-place so much slower than a vector?
Date: Fri, 25 Apr 2014 11:14:11 +0200 [thread overview]
Message-ID: <87zjj9n53w.fsf@igel.home> (raw)
In-Reply-To: <m338h1n7q1.fsf@gmail.com> (Leo Liu's message of "Fri, 25 Apr 2014 16:17:42 +0800")
Leo Liu <sdl.web@gmail.com> writes:
> Assume we are in a buffer visiting subr.el:
>
> (benchmark-run 1 (rev (buffer-string)))
> (11.774416366 1 0.060193897999999635)
>
> (benchmark-run 1 (rev (cl-coerce (buffer-string) 'vector)))
> (0.067042623 0 0.0)
>
> So why is this so much slower on string?
String random access has linear complexity: there is a single element
cache for the last known char->byte mapping for the last accessed
string, and the runtime depends on the distance from this point. Your
rev function represents the worst case behaviour.
Andreas.
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
next prev parent reply other threads:[~2014-04-25 9:14 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-25 8:12 why is reverse a string in-place so much slower than a vector? Leo Liu
2014-04-25 8:17 ` Leo Liu
2014-04-25 8:55 ` Rüdiger Sonderfeld
2014-04-25 9:14 ` Andreas Schwab [this message]
2014-04-25 9:35 ` Leo Liu
2014-04-25 11:00 ` Andreas Schwab
2014-04-26 0:19 ` Leo Liu
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