From: Stefan Monnier <monnier@iro.umontreal.ca>
To: Eli Zaretskii <eliz@gnu.org>
Cc: emacs-devel@gnu.org
Subject: Re: string_char_to_byte and string_byte_to_char micro-optimisation
Date: Sat, 15 Jun 2019 03:48:04 -0400 [thread overview]
Message-ID: <jwvblyzuwjk.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <83r27vweor.fsf@gnu.org> (Eli Zaretskii's message of "Sat, 15 Jun 2019 09:22:28 +0300")
>> ... and uses `aref` on it extensively.
> Right. And/or 'aset'.
Right, but `aset` is even more rare on multibyte strings.
> Other candidates are 'string-match' and 'replace-match'.
`replace-match` has to copy the string, so charpos<->bytepos conversion
doesn't slow it down significantly (I'd guess it's at most a factor of 2).
`string-match` is only affected by charpos<->bytepos is you use the
`start` argument, and the time to perform the actual regexp search will
usually dwarf the charpos<->bytepos conversion, so I think it can only
be noticeably slowed down by charpos<->bytepos conversion in
"pathological" cases where we `start` in the middle of a longish string
and we immediately find a short match.
In contrast, `aref` never does much more than the charpos<->bytepos
conversion itself.
Stefan
next prev parent reply other threads:[~2019-06-15 7:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-14 12:37 string_char_to_byte and string_byte_to_char micro-optimisation Robert Pluim
2019-06-14 16:53 ` Paul Eggert
2019-06-14 19:00 ` Eli Zaretskii
2019-06-14 20:11 ` Stefan Monnier
2019-06-15 6:22 ` Eli Zaretskii
2019-06-15 7:48 ` Stefan Monnier [this message]
2019-06-15 11:11 ` Noam Postavsky
2019-06-16 11:17 ` Stefan Monnier
2019-06-17 9:37 ` Robert Pluim
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