=item C<regnode_charclass>
-Character classes are represented by C<regnode_charclass> structures,
-which have a four-byte argument and then a 32-byte (256-bit) bitmap
-indicating which characters are included in the class.
+Bracketed character classes are represented by C<regnode_charclass>
+structures, which have a four-byte argument and then a 32-byte (256-bit)
+bitmap indicating which characters in the Latin1 range are included in
+the class.
regnode_charclass U32 arg1;
char bitmap[ANYOF_BITMAP_SIZE];
-=item C<regnode_charclass_class>
+Various flags whose names begin with C<ANYOF_> are used for special
+situations. Above Latin1 matches and things not known until run-time
+are stored in L</Perl's pprivate structure>.
+
+=item C<regnode_charclass_posixl>
There is also a larger form of a char class structure used to represent
-POSIX char classes called C<regnode_charclass_class> which has an
-additional 4-byte (32-bit) bitmap indicating which POSIX char classes
+POSIX char classes under C</l> matching,
+called C<regnode_charclass_posixl> which has an
+additional 32-bit bitmap indicating which POSIX char classes
have been included.
- regnode_charclass_class U32 arg1;
- char bitmap[ANYOF_BITMAP_SIZE];
- char classflags[ANYOF_CLASSBITMAP_SIZE];
+ regnode_charclass_posixl U32 arg1;
+ char bitmap[ANYOF_BITMAP_SIZE];
+ U32 classflags;
=back
The call graph looks like this:
- reg() # parse a top level regex, or inside of parens
- regbranch() # parse a single branch of an alternation
- regpiece() # parse a pattern followed by a quantifier
- regatom() # parse a simple pattern
- regclass() # used to handle a class
- reg() # used to handle a parenthesised subpattern
- ....
- ...
- regtail() # finish off the branch
- ...
- regtail() # finish off the branch sequence. Tie each
- # branch's tail to the tail of the sequence
- # (NEW) In Debug mode this is
- # regtail_study().
+ reg() # parse a top level regex, or inside of
+ # parens
+ regbranch() # parse a single branch of an alternation
+ regpiece() # parse a pattern followed by a quantifier
+ regatom() # parse a simple pattern
+ regclass() # used to handle a class
+ reg() # used to handle a parenthesised
+ # subpattern
+ ....
+ ...
+ regtail() # finish off the branch
+ ...
+ regtail() # finish off the branch sequence. Tie each
+ # branch's tail to the tail of the
+ # sequence
+ # (NEW) In Debug mode this is
+ # regtail_study().
A grammar form might be something like this:
piece : _piece
| _piece quant
+=head3 Parsing complications
+
+The implication of the above description is that a pattern containing nested
+parentheses will result in a call graph which cycles through C<reg()>,
+C<regbranch()>, C<regpiece()>, C<regatom()>, C<reg()>, C<regbranch()> I<etc>
+multiple times, until the deepest level of nesting is reached. All the above
+routines return a pointer to a C<regnode>, which is usually the last regnode
+added to the program. However, one complication is that reg() returns NULL
+for parsing C<(?:)> syntax for embedded modifiers, setting the flag
+C<TRYAGAIN>. The C<TRYAGAIN> propagates upwards until it is captured, in
+some cases by C<regatom()>, but otherwise unconditionally by
+C<regbranch()>. Hence it will never be returned by C<regbranch()> to
+C<reg()>. This flag permits patterns such as C<(?i)+> to be detected as
+errors (I<Quantifier follows nothing in regex; marked by <-- HERE in m/(?i)+
+<-- HERE />).
+
+Another complication is that the representation used for the program differs
+if it needs to store Unicode, but it's not always possible to know for sure
+whether it does until midway through parsing. The Unicode representation for
+the program is larger, and cannot be matched as efficiently. (See L</Unicode
+and Localisation Support> below for more details as to why.) If the pattern
+contains literal Unicode, it's obvious that the program needs to store
+Unicode. Otherwise, the parser optimistically assumes that the more
+efficient representation can be used, and starts sizing on this basis.
+However, if it then encounters something in the pattern which must be stored
+as Unicode, such as an C<\x{...}> escape sequence representing a character
+literal, then this means that all previously calculated sizes need to be
+redone, using values appropriate for the Unicode representation. Currently,
+all regular expression constructions which can trigger this are parsed by code
+in C<regatom()>.
+
+To avoid wasted work when a restart is needed, the sizing pass is abandoned
+- C<regatom()> immediately returns NULL, setting the flag C<RESTART_UTF8>.
+(This action is encapsulated using the macro C<REQUIRE_UTF8>.) This restart
+request is propagated up the call chain in a similar fashion, until it is
+"caught" in C<Perl_re_op_compile()>, which marks the pattern as containing
+Unicode, and restarts the sizing pass. It is also possible for constructions
+within run-time code blocks to turn out to need Unicode representation.,
+which is signalled by C<S_compile_runtime_code()> returning false to
+C<Perl_re_op_compile()>.
+
+The restart was previously implemented using a C<longjmp> in C<regatom()>
+back to a C<setjmp> in C<Perl_re_op_compile()>, but this proved to be
+problematic as the latter is a large function containing many automatic
+variables, which interact badly with the emergent control flow of C<setjmp>.
+
=head3 Debug Output
In the 5.9.x development version of perl you can C<< use re Debug => 'PARSE' >>
atom
>)$< 34 tail~ BRANCH (28)
36 tsdy~ BRANCH (END) (31)
- ~ attach to CLOSE1 (34) offset to 3
+ ~ attach to CLOSE1 (34) offset to 3
tsdy~ EXACT <foo> (EXACT) (29)
- ~ attach to CLOSE1 (34) offset to 5
+ ~ attach to CLOSE1 (34) offset to 5
tsdy~ EXACT <bar> (EXACT) (32)
- ~ attach to CLOSE1 (34) offset to 2
+ ~ attach to CLOSE1 (34) offset to 2
>$< tail~ BRANCH (3)
~ BRANCH (9)
~ TAIL (25)
and the second being running the regop interpreter.
If we can tell that there is no valid start point then we don't bother running
-interpreter at all. Likewise, if we know from the analysis phase that we
+the interpreter at all. Likewise, if we know from the analysis phase that we
cannot detect a short-cut to the start position, we go straight to the
interpreter.
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.)
+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
UTF-8 properly, both at compile time and at execution time, including
when the string and pattern are mismatched.
-The following comment in F<regcomp.h> gives an example of exactly how
-tricky this can be:
-
- Two problematic code points in Unicode casefolding of EXACT nodes:
-
- U+0390 - GREEK SMALL LETTER IOTA WITH DIALYTIKA AND TONOS
- U+03B0 - GREEK SMALL LETTER UPSILON WITH DIALYTIKA AND TONOS
-
- which casefold to
-
- Unicode UTF-8
-
- U+03B9 U+0308 U+0301 0xCE 0xB9 0xCC 0x88 0xCC 0x81
- U+03C5 U+0308 U+0301 0xCF 0x85 0xCC 0x88 0xCC 0x81
-
- This means that in case-insensitive matching (or "loose matching",
- as Unicode calls it), an EXACTF of length six (the UTF-8 encoded
- byte length of the above casefolded versions) can match a target
- string of length two (the byte length of UTF-8 encoded U+0390 or
- U+03B0). This would rather mess up the minimum length computation.
-
- What we'll do is to look for the tail four bytes, and then peek
- at the preceding two bytes to see whether we need to decrease
- the minimum length by four (six minus two).
-
- Thanks to the design of UTF-8, there cannot be false matches:
- A sequence of valid UTF-8 bytes cannot be a subsequence of
- another valid sequence of UTF-8 bytes.
-
-
=head2 Base Structures
The C<regexp> structure described in L<perlreapi> is common to all
-regex engines. Two of its fields that are intended for the private use
+regex engines. Two of its fields 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
implement things such as the stringification of C<qr//>.
-The other structure is pointed to be the C<regexp> struct's
+The other structure is pointed to by the C<regexp> struct's
C<pprivate> and is in addition to C<intflags> in the same struct
considered to be the property of the regex engine which compiled the
-regular expression;
+regular expression;
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
regex engine. Since it is specific to perl it 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;
+ typedef struct regexp_internal {
+ 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> formerly was an extra set of startp/endp stored in a
-C<regexp_paren_ofs> struct. This was used when the last successful match
-was from the same pattern as the current pattern, so that a partial
-match didn't overwrite the previous match's results, but it caused a
-problem with re-entrant code such as trying to build the UTF-8 swashes.
-Currently unused and left for backward compatibility with 5.10.0.
-
=item C<offsets>
Offsets holds a mapping of offset in the C<program>
=item C<data>
-This field points at a reg_data structure, which is defined as follows
+This field points at a C<reg_data> structure, which is defined as follows
struct reg_data {
U32 count;
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