=head1 DESCRIPTION
This document is an attempt to shine some light on the guts of the regex
-engine and how it works. The regex engine represents a signifigant chunk
+engine and how it works. The regex engine represents a significant chunk
of the perl codebase, but is relatively poorly understood. This document
is a meagre attempt at addressing this situation. It is derived from the
author's experience, comments in the source code, other papers on the
regex engine, feedback on the perl5-porters mail list, and no doubt other
places as well.
-B<WARNING!> It should be clearly understood that this document
-represents the state of the regex engine as the author understands it at
-the time of writing. It is B<NOT> an API definition; it is purely an
-internals guide for those who want to hack the regex engine, or
+B<WARNING!> It should be clearly understood that this document represents
+the state of the regex engine as the author understands it at the time of
+writing. Unless stated otherwise it is B<NOT> an API definition; it is
+purely an internals guide for those who want to hack the regex engine, or
understand how the regex engine works. Readers of this document are
-expected to understand perl's regex syntax and its usage in detail. If
-you want to learn about the basics of Perl's regular expressions, see
+expected to understand perl's regex syntax and its usage in detail. If you
+want to learn about the basics of Perl's regular expressions, see
L<perlre>.
=head1 OVERVIEW
"pattern" when we speak of their textual, source code form, the term
"program" when we speak of their internal representation. These
correspond to the terms I<S-regex> and I<B-regex> that Mark Jason
-Dominus employs in his paper on "Rx" ([1] in L</references>).
+Dominus employs in his paper on "Rx" ([1] in L</REFERENCES>).
=head2 What is a regular expression engine?
target string, and determines whether or not the string satisfies the
constraints. See L<perlre> for a full definition of the language.
-So in less grandiose terms the first part of the job is to turn a pattern into
+So in less grandiose terms the first part of the job is to turn a pattern into
something the computer can efficiently use to find the matching point in
the string, and the second part is performing the search itself.
The term "railroad normal form" is a bit esoteric, with "syntax
diagram/charts", or "railroad diagram/charts" being more common terms.
-Nevertheless it provides a useful mental image of a regex program: Each
+Nevertheless it provides a useful mental image of a regex program: each
node can be thought of as a unit of track, with a single entry and in
most cases a single exit point (there are pieces of track that fork, but
statistically not many), and the whole forms a layout with a
[end]
The truth of the matter is that perl's regular expressions these days are
-much more complex than this kind of structure, but visualizing it this way
-can help when trying to get your bearings, and it pretty closely with the
-current implementation.
+much more complex than this kind of structure, but visualising it this way
+can help when trying to get your bearings, and it matches the
+current implementation pretty closely.
To be more precise, we will say that a regex program is an encoding
of a graph. Each node in the graph corresponds to part of
The program is represented by an array of C<regnode> structures, one or
more of which represent a single regop of the program. Struct
-C<regnode> is the smallest struct needed and has a field structure which is
+C<regnode> is the smallest struct needed, and has a field structure which is
shared with all the other larger structures.
The "next" pointers of all regops except C<BRANCH> implement concatenation;
it is a regop leading into a sub-program. In particular, the operand
of a C<BRANCH> node is the first regop of the branch.
-B<NOTE>: As the railroad metaphor suggests this is B<not> a tree
+B<NOTE>: As the railroad metaphor suggests, this is B<not> a tree
structure: the tail of the branch connects to the thing following the
set of C<BRANCH>es. It is a like a single line of railway track that
splits as it goes into a station or railway yard and rejoins as it comes
Other larger C<regnode>-like structures are defined in F<regcomp.h>. They
are almost like subclasses in that they have the same fields as
-regnode, with possibly additional fields following in
+C<regnode>, with possibly additional fields following in
the structure, and in some cases the specific meaning (and name)
-of some of base fields are overriden. The following is a more
+of some of base fields are overridden. The following is a more
complete description.
=over 4
used.
A set of macros makes accessing the fields
-easier and more consistent. These include C<OP()> which is used to determine
-the type of a C<regnode>-like structure, C<NEXT_OFF()> which is the offset to
-the next node (more on this later)
, C<ARG()>, C<ARG1()>, C<ARG2()>, C<ARG_SET()>,
-and equivelents for reading and setting the arguments, C<STR_LEN()>,
+easier and more consistent. These include C<OP()>, which is used to determine
+the type of a C<regnode>-like structure; C<NEXT_OFF()>, which is the offset to
+the next node (more on this later)
; C<ARG()>, C<ARG1()>, C<ARG2()>, C<ARG_SET()>,
+and equivalents for reading and setting the arguments; and C<STR_LEN()>,
C<STRING()> and C<OPERAND()> for manipulating strings and regop bearing
types.
determined by whether the pattern involves interpolating any string
variables. If interpolation occurs, then compilation happens at run time. If it
does not, then compilation is performed at compile time. (The C</o> modifier changes this,
-as does C<qr//> to a certain extent). The engine doesn't really care that
+as does C<qr//> to a certain extent.) The engine doesn't really care that
much.
=head2 Compilation
This code resides primarily in F<regcomp.c>, along with the header files
F<regcomp.h>, F<regexp.h> and F<regnodes.h>.
-Compilation starts with C<pregcomp()>, which is mostly an initialization
-wrapper which farms out two other routines for the heavy lifting. The
-first being C<reg()> which is the start point for parsing, and
-C<study_chunk()> which is responsible for optimisation.
+Compilation starts with C<pregcomp()>, which is mostly an initialisation
+wrapper which farms work out to two other routines for the heavy lifting: the
+first is C<reg()>, which is the start point for parsing; the second,
+C<study_chunk()>, is responsible for optimisation.
-Initialization in C<pregcomp()> mostly involves the creation and data
-filling of a special structure C<RExC_state_t>, (defined in F<regcomp.c>).
-Almost all internally used routines in F<regcomp.h> take a pointer to one
+Initialisation in C<pregcomp()> mostly involves the creation and data-filling
+of a special structure, C<RExC_state_t> (defined in F<regcomp.c>).
+Almost all internally-used routines in F<regcomp.h> take a pointer to one
of these structures as their first argument, with the name C<pRExC_state>.
This structure is used to store the compilation state and contains many
fields. Likewise there are many macros which operate on this
-variable. Anything that looks like C<RExC_xxxx> is a macro that operates on
+variable: anything that looks like C<RExC_xxxx> is a macro that operates on
this pointer/structure.
=head3 Parsing for size
This stage is controlled by the macro C<SIZE_ONLY> being set.
-The parse procedes pretty much exactly as it does during the
+The parse proceeds pretty much exactly as it does during the
construction phase, except that most routines are short-circuited to
change the size field C<RExC_size> and not do anything else.
-=head3 Parsing for construcution
+=head3 Parsing for construction
Once the size of the program has been determined, the pattern is parsed
again, but this time for real. Now C<SIZE_ONLY> will be false, and the
C<reg()> is the start of the parse process. It is responsible for
parsing an arbitrary chunk of pattern up to either the end of the
string, or the first closing parenthesis it encounters in the pattern.
-This means it can be used to parse the toplevel regex, or any section
+This means it can be used to parse the top-level regex, or any section
inside of a grouping parenthesis. It also handles the "special parens"
that perl's regexes have. For instance when parsing C</x(?:foo)y/> C<reg()>
will at one point be called to parse from the "?" symbol up to and
A subtlety of the parsing process means that a regex like C</foo/> is
originally parsed into an alternation with a single branch. It is only
-afterwards that the optimizer converts single branch alternations into the
+afterwards that the optimiser converts single branch alternations into the
simpler form.
=head3 Parse Call Graph and a Grammar
regpiece() # parse a pattern followed by a quantifier
regatom() # parse a simple pattern
regclass() # used to handle a class
- reg() # used to handle a parenthesized subpattern
+ reg() # used to handle a parenthesised subpattern
....
...
regtail() # finish off the branch
...
regtail() # finish off the branch sequence. Tie each
- # branches tail to the tail of the sequence
+ # branch's tail to the tail of the sequence
# (NEW) In Debug mode this is
# regtail_study().
=head3 Debug Output
-In bleadperl you can C<< use re Debug => 'PARSE'; >> to see some trace
+In the 5.9.x development version of perl you can C<< use re Debug => 'PARSE'; >> to see some trace
information about the parse process. We will start with some simple
patterns and build up to more complex patterns.
So when we parse C</foo/> we see something like the following table. The
-left shows whats being parsed, the number indicates where the next regop
+left shows what is being parsed, and the number indicates where the next regop
would go. The stuff on the right is the trace output of the graph. The
names are chosen to be short to make it less dense on the screen. 'tsdy'
is a special form of C<regtail()> which does some extra analysis.
- >foo< 1 reg
- brnc
- piec
- atom
- >< 4 tsdy~ EXACT <foo> (EXACT) (1)
- ~ attach to END (3) offset to 2
+ >foo< 1 reg
+ brnc
+ piec
+ atom
+ >< 4 tsdy~ EXACT <foo> (EXACT) (1)
+ ~ attach to END (3) offset to 2
The resulting program then looks like:
the regop in the regnode array.
Now let's try a harder pattern. We will add a quantifier, so now we have the pattern
-C</foo+/>. We will see that C<regbranch()> calls C<regpiece()> regpiece twice.
-
- >foo+< 1 reg
- brnc
- piec
- atom
- >o+< 3 piec
- atom
- >< 6 tail~ EXACT <fo> (1)
- 7 tsdy~ EXACT <fo> (EXACT) (1)
- ~ PLUS (END) (3)
- ~ attach to END (6) offset to 3
+C</foo+/>. We will see that C<regbranch()> calls C<regpiece()> twice.
+
+ >foo+< 1 reg
+ brnc
+ piec
+ atom
+ >o+< 3 piec
+ atom
+ >< 6 tail~ EXACT <fo> (1)
+ 7 tsdy~ EXACT <fo> (EXACT) (1)
+ ~ PLUS (END) (3)
+ ~ attach to END (6) offset to 3
And we end up with the program:
6: END(0)
Now we have a special case. The C<EXACT> regop has a C<regnext> of 0. This is
-because if it matches it should try to match itself again. The PLUS regop
+because if it matches it should try to match itself again. The C<PLUS> regop
handles the actual failure of the C<EXACT> regop and acts appropriately (going
-to regnode 6 if the C<EXACT> matched at least once, or failing if it didn't.)
+to regnode 6 if the C<EXACT> matched at least once, or failing if it didn't).
Now for something much more complex: C</x(?:foo*|b[a][rR])(foo|bar)$/>
- >x(?:foo*|b... 1 reg
- brnc
+ >x(?:foo*|b... 1 reg
+ brnc
+ piec
+ atom
+ >(?:foo*|b[... 3 piec
+ atom
+ >?:foo*|b[a... reg
+ >foo*|b[a][... brnc
piec
atom
- >(?:foo*|b[... 3 piec
+ >o*|b[a][rR... 5 piec
+ atom
+ >|b[a][rR])... 8 tail~ EXACT <fo> (3)
+ >b[a][rR])(... 9 brnc
+ 10 piec
atom
- >?:foo*|b[a... reg
- >foo*|b[a][... brnc
- piec
- atom
- >o*|b[a][rR... 5 piec
- atom
- >|b[a][rR])... 8 tail~ EXACT <fo> (3)
- >b[a][rR])(... 9 brnc
- 10 piec
- atom
- >[a][rR])(f... 12 piec
- atom
- >a][rR])(fo... clas
- >[rR])(foo|... 14 tail~ EXACT <b> (10)
- piec
- atom
- >rR])(foo|b... clas
- >)(foo|bar)... 25 tail~ EXACT <a> (12)
- tail~ BRANCH (3)
- 26 tsdy~ BRANCH (END) (9)
- ~ attach to TAIL (25) offset to 16
- tsdy~ EXACT <fo> (EXACT) (4)
- ~ STAR (END) (6)
- ~ attach to TAIL (25) offset to 19
- tsdy~ EXACT <b> (EXACT) (10)
- ~ EXACT <a> (EXACT) (12)
- ~ ANYOF[Rr] (END) (14)
- ~ attach to TAIL (25) offset to 11
- >(foo|bar)$< tail~ EXACT <x> (1)
+ >[a][rR])(f... 12 piec
+ atom
+ >a][rR])(fo... clas
+ >[rR])(foo|... 14 tail~ EXACT <b> (10)
piec
atom
- >foo|bar)$< reg
- 28 brnc
- piec
- atom
- >|bar)$< 31 tail~ OPEN1 (26)
- >bar)$< brnc
- 32 piec
- atom
- >)$< 34 tail~ BRANCH (28)
- 36 tsdy~ BRANCH (END) (31)
- ~ attach to CLOSE1 (34) offset to 3
- tsdy~ EXACT <foo> (EXACT) (29)
- ~ attach to CLOSE1 (34) offset to 5
- tsdy~ EXACT <bar> (EXACT) (32)
- ~ attach to CLOSE1 (34) offset to 2
- >$< tail~ BRANCH (3)
- ~ BRANCH (9)
- ~ TAIL (25)
+ >rR])(foo|b... clas
+ >)(foo|bar)... 25 tail~ EXACT <a> (12)
+ tail~ BRANCH (3)
+ 26 tsdy~ BRANCH (END) (9)
+ ~ attach to TAIL (25) offset to 16
+ tsdy~ EXACT <fo> (EXACT) (4)
+ ~ STAR (END) (6)
+ ~ attach to TAIL (25) offset to 19
+ tsdy~ EXACT <b> (EXACT) (10)
+ ~ EXACT <a> (EXACT) (12)
+ ~ ANYOF[Rr] (END) (14)
+ ~ attach to TAIL (25) offset to 11
+ >(foo|bar)$< tail~ EXACT <x> (1)
+ piec
+ atom
+ >foo|bar)$< reg
+ 28 brnc
piec
atom
- >< 37 tail~ OPEN1 (26)
- ~ BRANCH (28)
- ~ BRANCH (31)
- ~ CLOSE1 (34)
- 38 tsdy~ EXACT <x> (EXACT) (1)
- ~ BRANCH (END) (3)
- ~ BRANCH (END) (9)
- ~ TAIL (END) (25)
- ~ OPEN1 (END) (26)
- ~ BRANCH (END) (28)
- ~ BRANCH (END) (31)
- ~ CLOSE1 (END) (34)
- ~ EOL (END) (36)
- ~ attach to END (37) offset to 1<div></div>
+ >|bar)$< 31 tail~ OPEN1 (26)
+ >bar)$< brnc
+ 32 piec
+ atom
+ >)$< 34 tail~ BRANCH (28)
+ 36 tsdy~ BRANCH (END) (31)
+ ~ attach to CLOSE1 (34) offset to 3
+ tsdy~ EXACT <foo> (EXACT) (29)
+ ~ attach to CLOSE1 (34) offset to 5
+ tsdy~ EXACT <bar> (EXACT) (32)
+ ~ attach to CLOSE1 (34) offset to 2
+ >$< tail~ BRANCH (3)
+ ~ BRANCH (9)
+ ~ TAIL (25)
+ piec
+ atom
+ >< 37 tail~ OPEN1 (26)
+ ~ BRANCH (28)
+ ~ BRANCH (31)
+ ~ CLOSE1 (34)
+ 38 tsdy~ EXACT <x> (EXACT) (1)
+ ~ BRANCH (END) (3)
+ ~ BRANCH (END) (9)
+ ~ TAIL (END) (25)
+ ~ OPEN1 (END) (26)
+ ~ BRANCH (END) (28)
+ ~ BRANCH (END) (31)
+ ~ CLOSE1 (END) (34)
+ ~ EOL (END) (36)
+ ~ attach to END (37) offset to 1
Resulting in the program
The C<(a|b)*> part can match at every char in the string, and then fail
every time because there is no C<z> in the string. So obviously we can
-avoid using the regex engine unless there is a 'z' in the string.
+avoid using the regex engine unless there is a C<z> in the string.
Likewise in a pattern like:
/foo(\w+)bar/
In this case we know that the string must contain a C<foo> which must be
-followed by C<bar>. We can use Fast Boyer-More matching as implemented
+followed by C<bar>. We can use Fast Boyer-Moore matching as implemented
in C<fbm_instr()> to find the location of these strings. If they don't exist
then we don't need to resort to the much more expensive regex engine.
Even better, if they do exist then we can use their positions to
There are various aspects of the pattern that can be used to facilitate
optimisations along these lines:
- * anchored fixed strings
- * floating fixed strings
- * minimum and maximum length requirements
- * start class
- * Beginning/End of line positions
+=over 5
+
+=item * anchored fixed strings
+
+=item * floating fixed strings
+
+=item * minimum and maximum length requirements
+
+=item * start class
+
+=item * Beginning/End of line positions
+
+=back
Another form of optimisation that can occur is post-parse "peep-hole"
optimisations, where inefficient constructs are replaced by
more efficient constructs. An example of this are C<TAIL> regops which are used
during parsing to mark the end of branches and the end of groups. These
-regops are used as place holders during construction and "always match"
+regops are used as place-holders during construction and "always match"
so they can be "optimised away" by making the things that point to the
-TAIL point to thing that the C<TAIL> points to, thus "skipping" the node.
+C<TAIL> point to thing that the C<TAIL> points to, thus "skipping" the node.
Another optimisation that can occur is that of "C<EXACT> merging" which is
where two consecutive C<EXACT> nodes are merged into a single
-regop. An even more agressive form of this is that a branch
-sequence of the form CEXACT BRANCH ... EXACT> can be converted into a
+regop. An even more aggressive form of this is that a branch
+sequence of the form C<EXACT BRANCH ... EXACT> can be converted into a
C<TRIE-EXACT> regop.
All of this occurs in the routine C<study_chunk()> which uses a special
The two entry points are C<re_intuit_start()> and C<pregexec()>. These routines
have a somewhat incestuous relationship with overlap between their functions,
and C<pregexec()> may even call C<re_intuit_start()> on its own. Nevertheless
-the perl source code may call into either, or both.
+other parts of the the perl source code may call into either, or both.
Execution of the interpreter itself used to be recursive. Due to the
-efforts of Dave Mitchell in blead perl, it is now iterative. Now an
+efforts of Dave Mitchell in the 5.9.x development track, it is now iterative. Now an
internal stack is maintained on the heap and the routine is fully
iterative. This can make it tricky as the code is quite conservative
-about what state it stores which means that two consecutive lines in the
+about what state it stores, with the result that that two consecutive lines in the
code can actually be running in totally different contexts due to the
simulated recursion.
=head3 Start position and no-match optimisations
-C<re_intuit_start()> is responsible for handling start points and no match
+C<re_intuit_start()> is responsible for handling start points and no-match
optimisations as determined by the results of the analysis done by
C<study_chunk()> (and described in L<Peep-hole Optimisation and Analysis>).
-The basic structure of this routine is to try to find the start and/or
-end points of where the pattern could match, and to ensure that the string
-is long enough to match the pattern. It tries to use more efficent
-methods over less efficient methods and may involve considerable cross
-checking of constraints to find the place in the string that matches.
+The basic structure of this routine is to try to find the start- and/or
+end-points of where the pattern could match, and to ensure that the string
+is long enough to match the pattern. It tries to use more efficient
+methods over less efficient methods and may involve considerable
+cross-checking of constraints to find the place in the string that matches.
For instance it may try to determine that a given fixed string must be
not only present but a certain number of chars before the end of the
string, or whatever.
It calls several other routines, such as C<fbm_instr()> which does
-"Fast Boyer More" matching and C<find_byclass()> which is responsible for
+Fast Boyer Moore matching and C<find_byclass()> which is responsible for
finding the start using the first mandatory regop in the program.
-When the optimisation criteria have been satisfied C<reg_try()> is called
+When the optimisation criteria have been satisfied, C<reg_try()> is called
to perform the match.
=head3 Program execution
C<pregexec()> is the main entry point for running a regex. It contains
-support for initializing the regex interpreters state, running
-C<re_intuit_start()> if needed, and running the intepreter on the string
-from various start positions as needed. When its necessary to use
+support for initialising the regex interpreter's state, running
+C<re_intuit_start()> if needed, and running the interpreter on the string
+from various start positions as needed. When it is necessary to use
the regex interpreter C<pregexec()> calls C<regtry()>.
C<regtry()> is the entry point into the regex interpreter. It expects
as arguments a pointer to a C<regmatch_info> structure and a pointer to
a string. It returns an integer 1 for success and a 0 for failure.
-It is basically a setup wrapper around C<regmatch()>.
+It is basically a set-up wrapper around C<regmatch()>.
C<regmatch> is the main "recursive loop" of the interpreter. It is
-basically a giant switch statement that executes the regops based on
-their type. A few of the regops are implemented as subroutines but
-the bulk are inline code.
+basically a giant switch statement that implements a state machine, where
+the possible states are the regops themselves, plus a number of additional
+intermediate and failure states. A few of the states are implemented as
+subroutines but the bulk are inline code.
=head1 MISCELLANEOUS
-=head2 UNICODE and Localization Support
+=head2 Unicode and Localisation Support
+
+When dealing with strings containing characters that cannot be represented
+using an eight-bit character set, perl uses an internal representation
+that is a permissive version of Unicode's UTF-8 encoding[2]. This uses single
+bytes to represent characters from the ASCII character set, and sequences
+of two or more bytes for all other characters. (See L<perlunitut>
+for more information about the relationship between UTF-8 and perl's
+encoding, utf8 -- the difference isn't important for this discussion.)
No matter how you look at it, Unicode support is going to be a pain in a
regex engine. Tricks that might be fine when you have 256 possible
characters often won't scale to handle the size of the UTF-8 character
set. Things you can take for granted with ASCII may not be true with
-unicode. For instance, in ASCII, it is safe to assume that
+Unicode. For instance, in ASCII, it is safe to assume that
C<sizeof(char1) == sizeof(char2)>, but in UTF-8 it isn't. Unicode case folding is
vastly more complex than the simple rules of ASCII, and even when not
-using Unicode but only localized single byte encodings, things can get
-tricky (for example, GERMAN-SHARP-ESS should match 'ss' in localized case
-insensitive matching).
+using Unicode but only localised single byte encodings, things can get
+tricky (for example, GERMAN-SHARP-ESS should match 'SS' in localised
+case-insensitive matching).
Making things worse is that UTF-8 support was a later addition to the
regex engine (as it was to perl) and this necessarily made things a lot
Unicode support in mind from the beginning than it is to retrofit it to
one that wasn't.
-Nearly all regops that involves looking at the input string have
+Nearly all regops that involve looking at the input string have
two cases, one for UTF-8, and one not. In fact, it's often more complex
than that, as the pattern may be UTF-8 as well.
A sequence of valid UTF-8 bytes cannot be a subsequence of
another valid sequence of UTF-8 bytes.
-=head3 Base Struct
-regexp.h contains the base structure definition:
+=head2 Base Structures
+
+There are two structures used to store a compiled regular expression.
+One, the regexp structure is considered to be perl's property, and the
+other is considered to be the property of the regex engine which
+compiled the regular expression; in the case of the stock engine this
+structure is called regexp_internal.
+
+The regexp structure contains all the data that perl needs to be aware of
+to properly work with the regular expression. It includes data about
+optimisations that perl can use to determine if the regex engine should
+really be used, and various other control info that is needed to properly
+execute patterns in various contexts such as is the pattern anchored in
+some way, or what flags were used during the compile, or whether the
+program contains special constructs that perl needs to be aware of.
+
+In addition it contains two fields that are intended for the private use
+of the regex engine that compiled the pattern. These are the C<intflags>
+and pprivate members. The C<pprivate> is a void pointer to an arbitrary
+structure whose use and management is the responsibility of the compiling
+engine. perl will never modify either of these values.
+
+As mentioned earlier, in the case of the default engines, the C<pprivate>
+will be a pointer to a regexp_internal structure which holds the compiled
+program and any additional data that is private to the regex engine
+implementation.
+
+=head3 Perl Inspectable Data About Pattern
+
+F<regexp.h> contains the "public" structure definition. All regex engines
+must be able to correctly build a regexp structure.
typedef struct regexp {
- I32 *startp;
- I32 *endp;
- regnode *regstclass;
- struct reg_substr_data *substrs;
- char *precomp; /* pre-compilation regular expression */
- struct reg_data *data; /* Additional data. */
- char *subbeg; /* saved or original string
+ /* what engine created this regexp? */
+ const struct regexp_engine* engine;
+
+ /* Information about the match that the perl core uses to manage things */
+ U32 extflags; /* Flags used both externally and internally */
+ I32 minlen; /* mininum possible length of string to match */
+ I32 minlenret; /* mininum possible length of $& */
+ U32 gofs; /* chars left of pos that we search from */
+ struct reg_substr_data *substrs; /* substring data about strings that must appear
+ in the final match, used for optimisations */
+ U32 nparens; /* number of capture buffers */
+
+ /* private engine specific data */
+ U32 intflags; /* Engine Specific Internal flags */
+ void *pprivate; /* Data private to the regex engine which
+ created this object. */
+
+ /* Data about the last/current match. These are modified during matching*/
+ U32 lastparen; /* last open paren matched */
+ U32 lastcloseparen; /* last close paren matched */
+ I32 *startp; /* Array of offsets from start of string (@-) */
+ I32 *endp; /* Array of offsets from start of string (@+) */
+ char *subbeg; /* saved or original string
so \digit works forever. */
- #ifdef PERL_OLD_COPY_ON_WRITE
- SV *saved_copy; /* If non-NULL, SV which is COW from original */
- #endif
- U32 *offsets; /* offset annotations 20001228 MJD */
I32 sublen; /* Length of string pointed by subbeg */
- I32 refcnt;
- I32 minlen; /* mininum possible length of $& */
+ SV_SAVED_COPY /* If non-NULL, SV which is COW from original */
+
+
+ /* Information about the match that isn't often used */
+ char *precomp; /* pre-compilation regular expression */
I32 prelen; /* length of precomp */
- U32 nparens; /* number of parentheses */
- U32 lastparen; /* last paren matched */
- U32 lastcloseparen; /* last paren matched */
- U32 reganch; /* Internal use only +
- Tainted information used by regexec? */
- regnode program[1]; /* Unwarranted chumminess with compiler. */
+ I32 seen_evals; /* number of eval groups in the pattern - for security checks */
+ HV *paren_names; /* Optional hash of paren names */
+
+ /* Refcount of this regexp */
+ I32 refcnt; /* Refcount of this regexp */
} regexp;
-C<program>, and C<data> are the primary fields of concern in terms of
-program structure. program is the actual array of nodes, and data is
-an array of "whatever", with each whatever being typed by letter, and
-freed or cloned as needed based on this type. regops use the data
-array to store reference data that isn't convenient to store in the regop
-itself. It also means memory management code doesnt need to traverse the
-program to find pointers. So for instance if a regop needs a pointer, the
-normal procedure is use a regnode_arg1 store the data index in the ARG
-field and look it up from the data array.
+The fields are discussed in more detail below:
+
+=over 5
+
+
+=item C<refcnt>
+
+The number of times the structure is referenced. When this falls to 0
+the regexp is automatically freed by a call to pregfree.
+
+=item C<engine>
+
+This field points at a regexp_engine structure which contains pointers
+to the subroutine that are to be used for performing a match. It
+is the compiling routines responsibility to populate this field before
+returning the regexp object.
+
+=item C<precomp> C<prelen>
+
+Used for debugging purposes. C<precomp> holds a copy of the pattern
+that was compiled.
+
+=item C<extflags>
+
+This is used to store various flags about the pattern, such as whether it
+contains a \G or a ^ or $ symbol.
+
+=item C<minlen> C<minlenret>
+
+C<minlen> is the minimum string length required for the pattern to match.
+This is used to prune the search space by not bothering to match any
+closer to the end of a string than would allow a match. For instance
+there is no point in even starting the regex engine if the minlen is
+10 but the string is only 5 characters long. There is no way that the
+pattern can match.
+
+C<minlenret> is the minimum length of the string that would be found
+in $& after a match.
+
+The difference between C<minlen> and C<minlenret> can be seen in the
+following pattern:
+
+ /ns(?=\d)/
+
+where the C<minlen> would be 3 but the minlen ret would only be 2 as
+the \d is required to match but is not actually included in the matched
+content. This distinction is particularly important as the substitution
+logic uses the C<minlenret> to tell whether it can do in-place substition
+which can result in considerable speedup.
+
+=item C<gofs>
+
+Left offset from pos() to start match at.
+
+=item C<nparens>, C<lasparen>, and C<lastcloseparen>
+
+These fields are used to keep track of how many paren groups could be matched
+in the pattern, which was the last open paren to be entered, and which was
+the last close paren to be entered.
+
+=item C<paren_names>
+
+This is a hash used internally to track named capture buffers and their
+offsets. The keys are the names of the buffers the values are dualvars,
+with the IV slot holding the number of buffers with the given name and the
+pv being an embedded array of I32. The values may also be contained
+independently in the data array in cases where named backreferences are
+used.
+
+=item C<reg_substr_data>
+
+Holds information on the longest string that must occur at a fixed
+offset from the start of the pattern, and the longest string that must
+occur at a floating offset from the start of the pattern. Used to do
+Fast-Boyer-Moore searches on the string to find out if its worth using
+the regex engine at all, and if so where in the string to search.
-startp,endp,nparens,lasparen,lastcloseparen are used to manage capture
-buffers.
+=item C<startp>, C<endp>,
-subbeg and optional saved_copy are used during exectuion phase for managing
-replacements.
+These fields store arrays that are used to hold the offsets of the begining
+and end of each capture group that has matched. -1 is used to indicate no match.
-offsets and precomp are used for debugging purposes.
+These are the source for @- and @+.
-And the rest are used for start point optimisations.
+=item C<subbeg> C<sublen> C<saved_copy>
+These are used during execution phase for managing search and replace
+patterns.
-=head2 Deallocation and Cloning
+=item C<seen_evals>
+
+This stores the number of eval groups in the pattern. This is used
+for security purposes when embedding compiled regexes into larger
+patterns.
+
+=back
+
+=head3 Engine Private Data About Pattern
+
+Additionally regexp.h contains the following "private" definition which is perl
+specific and is only of curiosity value to other engine implementations.
+
+ typedef struct regexp_internal {
+ regexp_paren_ofs *swap; /* Swap copy of *startp / *endp */
+ U32 *offsets; /* offset annotations 20001228 MJD
+ data about mapping the program to the
+ string*/
+ regnode *regstclass; /* Optional startclass as identified or constructed
+ by the optimiser */
+ struct reg_data *data; /* Additional miscellaneous data used by the program.
+ Used to make it easier to clone and free arbitrary
+ data that the regops need. Often the ARG field of
+ a regop is an index into this structure */
+ regnode program[1]; /* Unwarranted chumminess with compiler. */
+ } regexp_internal;
+
+=over 5
+
+=item C<swap>
+
+C<swap> is an extra set of startp/endp stored in a C<regexp_paren_ofs>
+struct. This is used when the last successful match was from same pattern
+as the current pattern, so that a partial match doesn't overwrite the
+previous match's results. When this field is data filled the matching
+engine will swap buffers before every match attempt. If the match fails,
+then it swaps them back. If it's successful it leaves them. This field
+is populated on demand and is by default null.
+
+=item C<offsets>
+
+Offsets holds a mapping of offset in the C<program>
+to offset in the C<precomp> string. This is only used by ActiveStates
+visual regex debugger.
+
+=item C<regstclass>
+
+Special regop that is used by C<re_intuit_start()> to check if a pattern
+can match at a certain position. For instance if the regex engine knows
+that the pattern must start with a 'Z' then it can scan the string until
+it finds one and then launch the regex engine from there. The routine
+that handles this is called C<find_by_class()>. Sometimes this field
+points at a regop embedded in the program, and sometimes it points at
+an independent synthetic regop that has been constructed by the optimiser.
+
+=item C<data>
+
+This field points at a reg_data structure, which is defined as follows
+
+ struct reg_data {
+ U32 count;
+ U8 *what;
+ void* data[1];
+ };
+
+This structure is used for handling data structures that the regex engine
+needs to handle specially during a clone or free operation on the compiled
+product. Each element in the data array has a corresponding element in the
+what array. During compilation regops that need special structures stored
+will add an element to each array using the add_data() routine and then store
+the index in the regop.
+
+=item C<program>
+
+Compiled program. Inlined into the structure so the entire struct can be
+treated as a single blob.
+
+=back
+
+=head2 Pluggable Interface
+
+As of Perl 5.9.5 there is a new interface for using other regexp engines
+than the default one. Each engine is supposed to provide access to
+a constant structure of the following format:
+
+ typedef struct regexp_engine {
+ regexp* (*comp) (pTHX_ char* exp, char* xend, PMOP* pm);
+ I32 (*exec) (pTHX_ regexp* prog, char* stringarg, char* strend,
+ char* strbeg, I32 minend, SV* screamer,
+ void* data, U32 flags);
+ char* (*intuit) (pTHX_ regexp *prog, SV *sv, char *strpos,
+ char *strend, U32 flags,
+ struct re_scream_pos_data_s *data);
+ SV* (*checkstr) (pTHX_ regexp *prog);
+ void (*free) (pTHX_ struct regexp* r);
+ #ifdef USE_ITHREADS
+ void* (*dupe) (pTHX_ const regexp *r, CLONE_PARAMS *param);
+ #endif
+ } regexp_engine;
+
+When a regexp is compiled its C<engine> field is then set to point at
+the appropriate structure so that when it needs to be used Perl can find
+the right routines to do so.
+
+In order to install a new regexp handler, C<$^H{regcomp}> is set
+to an integer which (when casted appropriately) resolves to one of these
+structures. When compiling the C<comp> method is executed, and the
+resulting regexp structures engine field is expected to point back at
+the same structure.
+
+The pTHX_ symbol in the definition is a macro used by perl under threading
+to provide an extra argument to the routine holding a pointer back to
+the interpreter that is executing the regexp. So under threading all
+routines get an extra argument.
+
+The routines are as follows:
+
+=over 4
+
+=item comp
+
+ regexp* comp(char *exp, char *xend, PMOP pm);
+
+Compile the pattern between exp and xend using the flags contained in
+pm and return a pointer to a prepared regexp structure that can perform
+the match.
+
+=item exec
+
+ I32 exec(regexp* prog,
+ char *stringarg, char* strend, char* strbeg,
+ I32 minend, SV* screamer,
+ void* data, U32 flags);
+
+Execute a regexp.
+
+=item intuit
+
+ char* intuit( regexp *prog,
+ SV *sv, char *strpos, char *strend,
+ U32 flags, struct re_scream_pos_data_s *data);
+
+Find the start position where a regex match should be attempted,
+or possibly whether the regex engine should not be run because the
+pattern can't match. This is called as appropriate by the core
+depending on the values of the extflags member of the regexp
+structure.
+
+=item checkstr
+
+ SV* checkstr(regexp *prog);
+
+Return a SV containing a string that must appear in the pattern. Used
+for optimising matches.
+
+=item free
+
+ void free(regexp *prog);
+
+Called by perl when it is freeing a regexp pattern so that the engine
+can release any resources pointed to by the C<pprivate> member of the
+regexp structure. This is only responsible for freeing private data,
+perl will handle releasing anything else contained in the regexp structure.
+
+=item dupe
+
+ void* dupe(const regexp *r, CLONE_PARAMS *param);
+
+On threaded builds a regexp may need to be duplicated so that the pattern
+can be used by mutiple threads. This routine is expected to handle the
+duplication of any private data pointed to by the C<pprivate> member of
+the regexp structure. It will be called with the preconstructed new
+regexp structure as an argument, the C<pprivate> member will point at
+the B<old> private structue, and it is this routines responsibility to
+construct a copy and return a pointer to it (which perl will then use to
+overwrite the field as passed to this routine.)
+
+This allows the engine to dupe its private data but also if necessary
+modify the final structure if it really must.
+
+On unthreaded builds this field doesn't exist.
+
+=back
+
+
+=head2 De-allocation and Cloning
Any patch that adds data items to the regexp will need to include
-changes to sv.c (Perl_re_dup) and regcomp.c (pregfree). This
+changes to F<sv.c> (C<Perl_re_dup()>) and F<regcomp.c> (C<pregfree()>). This
involves freeing or cloning items in the regexes data array based
-on the data items type.
+on the data item's type.
+
+=head1 SEE ALSO
+
+L<perlre>
+
+L<perlunitut>
=head1 AUTHOR
Ronald J. Kimball, Dave Mitchell, Dominic Dunlop, Mark Jason Dominus,
Stephen McCamant, and David Landgren.
-=head1 LICENSE
+=head1 LICENCE
Same terms as Perl.
=head1 REFERENCES
-[1] http://perl.plover.com/Rx/paper/
+[1] L<http://perl.plover.com/Rx/paper/>
+
+[2] L<http://www.unicode.org>
=cut
https://perl5.git.perl.org / perl5.git / blobdiff