1 files changed, 66 insertions, 0 deletions
diff --git a/external-libs/pcre/doc/pcreperform.3 b/external-libs/pcre/doc/pcreperform.3
new file mode 100644
index 00000000..52a332fc
--- /dev/null
+++ b/external-libs/pcre/doc/pcreperform.3
@@ -0,0 +1,66 @@
+.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.