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Re: Performance tips when using regular expressions (regexps) in font-lo

From: David Combs
Subject: Re: Performance tips when using regular expressions (regexps) in font-locking
Date: Sun, 16 Dec 2007 18:28:13 +0000 (UTC)

In article <address@hidden>,
Stefan Monnier  <address@hidden> wrote:
>> I have enhanced my cc-mode with extra font-locking for assignments,
>> function calls, numerical literals, operators and even format strings
>> to the [sf]?printf-functions. The regular expressions describing these
>> context are quite complicated and as a result my cc-mode is no longer
>> as snappy as without my enhancement. Does any have any tips on how to
>> write regular expressions when performance is crucial? For example
>> should I use [:space:] instead of [ \t]? Should I post the coden
>> aswell?
>I believe inmost cases micro-optimization such as choosing between
>[[:space:]] and [ \t] will make no noticeable difference.
>But you should pay attention to * and + operators, especially when
>nested or when adjacent and make sure that there is no redundancy: there
>should ideally be only one way for the regexp to match a given piece
>of text.
>E.g. avoid [ab]*a*
>        Stefan

Friedel's "Regular Expressions" book (O'Reilly) (cheaper from,
 the *bible* on regexps (*hundreds* of pages long) has an entire chapter
 devoted to optimizing your regexps.  Essential reading.

 (You may *think* you know something about regexps -- read that book,
  and you'll know different! :-)


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