From f3bf8d3110b852b8f338898c3237d16a74360cf3 Mon Sep 17 00:00:00 2001 From: Jay Berkenbilt Date: Sat, 10 Oct 2009 17:41:30 +0000 Subject: remove files not needed for building git-svn-id: svn+q:///qpdf/trunk@767 71b93d88-0707-0410-a8cf-f5a4172ac649 --- external-libs/pcre/doc/pcreperform.3 | 66 ------------------------------------ 1 file changed, 66 deletions(-) delete mode 100644 external-libs/pcre/doc/pcreperform.3 (limited to 'external-libs/pcre/doc/pcreperform.3') diff --git a/external-libs/pcre/doc/pcreperform.3 b/external-libs/pcre/doc/pcreperform.3 deleted file mode 100644 index 52a332fc..00000000 --- a/external-libs/pcre/doc/pcreperform.3 +++ /dev/null @@ -1,66 +0,0 @@ -.TH PCRE 3 -.SH NAME -PCRE - Perl-compatible regular expressions -.SH PCRE PERFORMANCE -.rs -.sp -Certain items that may appear in regular expression patterns are more efficient -than others. It is more efficient to use a character class like [aeiou] than a -set of alternatives such as (a|e|i|o|u). In general, the simplest construction -that provides the required behaviour is usually the most efficient. Jeffrey -Friedl's book contains a lot of discussion about optimizing regular expressions -for efficient performance. - -When a pattern begins with .* not in parentheses, or in parentheses that are -not the subject of a backreference, and the PCRE_DOTALL option is set, the -pattern is implicitly anchored by PCRE, since it can match only at the start of -a subject string. However, if PCRE_DOTALL is not set, PCRE cannot make this -optimization, because the . metacharacter does not then match a newline, and if -the subject string contains newlines, the pattern may match from the character -immediately following one of them instead of from the very start. For example, -the pattern - - .*second - -matches the subject "first\\nand second" (where \\n stands for a newline -character), with the match starting at the seventh character. In order to do -this, PCRE has to retry the match starting after every newline in the subject. - -If you are using such a pattern with subject strings that do not contain -newlines, the best performance is obtained by setting PCRE_DOTALL, or starting -the pattern with ^.* to indicate explicit anchoring. That saves PCRE from -having to scan along the subject looking for a newline to restart at. - -Beware of patterns that contain nested indefinite repeats. These can take a -long time to run when applied to a string that does not match. Consider the -pattern fragment - - (a+)* - -This can match "aaaa" in 33 different ways, and this number increases very -rapidly as the string gets longer. (The * repeat can match 0, 1, 2, 3, or 4 -times, and for each of those cases other than 0, the + repeats can match -different numbers of times.) When the remainder of the pattern is such that the -entire match is going to fail, PCRE has in principle to try every possible -variation, and this can take an extremely long time. - -An optimization catches some of the more simple cases such as - - (a+)*b - -where a literal character follows. Before embarking on the standard matching -procedure, PCRE checks that there is a "b" later in the subject string, and if -there is not, it fails the match immediately. However, when there is no -following literal this optimization cannot be used. You can see the difference -by comparing the behaviour of - - (a+)*\\d - -with the pattern above. The former gives a failure almost instantly when -applied to a whole line of "a" characters, whereas the latter takes an -appreciable time with strings longer than about 20 characters. - -.in 0 -Last updated: 03 February 2003 -.br -Copyright (c) 1997-2003 University of Cambridge. -- cgit v1.2.3-54-g00ecf