pcreperform specification

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/html/pcreperform.html | 93 ---------------------------- 1 file changed, 93 deletions(-) delete mode 100644 external-libs/pcre/doc/html/pcreperform.html (limited to 'external-libs/pcre/doc/html/pcreperform.html') diff --git a/external-libs/pcre/doc/html/pcreperform.html b/external-libs/pcre/doc/html/pcreperform.html deleted file mode 100644 index 418ac6d4..00000000 --- a/external-libs/pcre/doc/html/pcreperform.html +++ /dev/null @@ -1,93 +0,0 @@ - - -pcreperform specification - - -This HTML document has been generated automatically from the original man page. -If there is any nonsense in it, please consult the man page, in case the -conversion went wrong.
-

PCRE PERFORMANCE -

-
PCRE PERFORMANCE
-

-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. -