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1  ChangeLog for PCRE  ChangeLog for PCRE
2  ------------------  ------------------
4    Version 7.4 10-Sep-07
5    ---------------------
7    1.  Change 7.3/28 was implemented for classes by looking at the bitmap. This
8        means that a class such as [\s] counted as "explicit reference to CR or
9        LF". That isn't really right - the whole point of the change was to try to
10        help when there was an actual mention of one of the two characters. So now
11        the change happens only if \r or \n (or a literal CR or LF) character is
12        encountered.
14    2.  The 32-bit options word was also used for 6 internal flags, but the numbers
15        of both had grown to the point where there were only 3 bits left.
16        Fortunately, there was spare space in the data structure, and so I have
17        moved the internal flags into a new 16-bit field to free up more option
18        bits.
20    3.  The appearance of (?J) at the start of a pattern set the DUPNAMES option,
21        but did not set the internal JCHANGED flag - either of these is enough to
22        control the way the "get" function works - but the PCRE_INFO_JCHANGED
23        facility is supposed to tell if (?J) was ever used, so now (?J) at the
24        start sets both bits.
27    Version 7.3 28-Aug-07
28    ---------------------
30     1. In the rejigging of the build system that eventually resulted in 7.1, the
31        line "#include <pcre.h>" was included in pcre_internal.h. The use of angle
32        brackets there is not right, since it causes compilers to look for an
33        installed pcre.h, not the version that is in the source that is being
34        compiled (which of course may be different). I have changed it back to:
36          #include "pcre.h"
38        I have a vague recollection that the change was concerned with compiling in
39        different directories, but in the new build system, that is taken care of
40        by the VPATH setting the Makefile.
42     2. The pattern .*$ when run in not-DOTALL UTF-8 mode with newline=any failed
43        when the subject happened to end in the byte 0x85 (e.g. if the last
44        character was \x{1ec5}). *Character* 0x85 is one of the "any" newline
45        characters but of course it shouldn't be taken as a newline when it is part
46        of another character. The bug was that, for an unlimited repeat of . in
47        not-DOTALL UTF-8 mode, PCRE was advancing by bytes rather than by
48        characters when looking for a newline.
50     3. A small performance improvement in the DOTALL UTF-8 mode .* case.
52     4. Debugging: adjusted the names of opcodes for different kinds of parentheses
53        in debug output.
55     5. Arrange to use "%I64d" instead of "%lld" and "%I64u" instead of "%llu" for
56        long printing in the pcrecpp unittest when running under MinGW.
58     6. ESC_K was left out of the EBCDIC table.
60     7. Change 7.0/38 introduced a new limit on the number of nested non-capturing
61        parentheses; I made it 1000, which seemed large enough. Unfortunately, the
62        limit also applies to "virtual nesting" when a pattern is recursive, and in
63        this case 1000 isn't so big. I have been able to remove this limit at the
64        expense of backing off one optimization in certain circumstances. Normally,
65        when pcre_exec() would call its internal match() function recursively and
66        immediately return the result unconditionally, it uses a "tail recursion"
67        feature to save stack. However, when a subpattern that can match an empty
68        string has an unlimited repetition quantifier, it no longer makes this
69        optimization. That gives it a stack frame in which to save the data for
70        checking that an empty string has been matched. Previously this was taken
71        from the 1000-entry workspace that had been reserved. So now there is no
72        explicit limit, but more stack is used.
74     8. Applied Daniel's patches to solve problems with the import/export magic
75        syntax that is required for Windows, and which was going wrong for the
76        pcreposix and pcrecpp parts of the library. These were overlooked when this
77        problem was solved for the main library.
79     9. There were some crude static tests to avoid integer overflow when computing
80        the size of patterns that contain repeated groups with explicit upper
81        limits. As the maximum quantifier is 65535, the maximum group length was
82        set at 30,000 so that the product of these two numbers did not overflow a
83        32-bit integer. However, it turns out that people want to use groups that
84        are longer than 30,000 bytes (though not repeat them that many times).
85        Change 7.0/17 (the refactoring of the way the pattern size is computed) has
86        made it possible to implement the integer overflow checks in a much more
87        dynamic way, which I have now done. The artificial limitation on group
88        length has been removed - we now have only the limit on the total length of
89        the compiled pattern, which depends on the LINK_SIZE setting.
91    10. Fixed a bug in the documentation for get/copy named substring when
92        duplicate names are permitted. If none of the named substrings are set, the
93        functions return PCRE_ERROR_NOSUBSTRING (7); the doc said they returned an
94        empty string.
96    11. Because Perl interprets \Q...\E at a high level, and ignores orphan \E
97        instances, patterns such as [\Q\E] or [\E] or even [^\E] cause an error,
98        because the ] is interpreted as the first data character and the
99        terminating ] is not found. PCRE has been made compatible with Perl in this
100        regard. Previously, it interpreted [\Q\E] as an empty class, and [\E] could
101        cause memory overwriting.
103    10. Like Perl, PCRE automatically breaks an unlimited repeat after an empty
104        string has been matched (to stop an infinite loop). It was not recognizing
105        a conditional subpattern that could match an empty string if that
106        subpattern was within another subpattern. For example, it looped when
107        trying to match  (((?(1)X|))*)  but it was OK with  ((?(1)X|)*)  where the
108        condition was not nested. This bug has been fixed.
110    12. A pattern like \X?\d or \P{L}?\d in non-UTF-8 mode could cause a backtrack
111        past the start of the subject in the presence of bytes with the top bit
112        set, for example "\x8aBCD".
114    13. Added Perl 5.10 experimental backtracking controls (*FAIL), (*F), (*PRUNE),
115        (*SKIP), (*THEN), (*COMMIT), and (*ACCEPT).
117    14. Optimized (?!) to (*FAIL).
119    15. Updated the test for a valid UTF-8 string to conform to the later RFC 3629.
120        This restricts code points to be within the range 0 to 0x10FFFF, excluding
121        the "low surrogate" sequence 0xD800 to 0xDFFF. Previously, PCRE allowed the
122        full range 0 to 0x7FFFFFFF, as defined by RFC 2279. Internally, it still
123        does: it's just the validity check that is more restrictive.
125    16. Inserted checks for integer overflows during escape sequence (backslash)
126        processing, and also fixed erroneous offset values for syntax errors during
127        backslash processing.
129    17. Fixed another case of looking too far back in non-UTF-8 mode (cf 12 above)
130        for patterns like [\PPP\x8a]{1,}\x80 with the subject "A\x80".
132    18. An unterminated class in a pattern like (?1)\c[ with a "forward reference"
133        caused an overrun.
135    19. A pattern like (?:[\PPa*]*){8,} which had an "extended class" (one with
136        something other than just ASCII characters) inside a group that had an
137        unlimited repeat caused a loop at compile time (while checking to see
138        whether the group could match an empty string).
140    20. Debugging a pattern containing \p or \P could cause a crash. For example,
141        [\P{Any}] did so. (Error in the code for printing property names.)
143    21. An orphan \E inside a character class could cause a crash.
145    22. A repeated capturing bracket such as (A)? could cause a wild memory
146        reference during compilation.
148    23. There are several functions in pcre_compile() that scan along a compiled
149        expression for various reasons (e.g. to see if it's fixed length for look
150        behind). There were bugs in these functions when a repeated \p or \P was
151        present in the pattern. These operators have additional parameters compared
152        with \d, etc, and these were not being taken into account when moving along
153        the compiled data. Specifically:
155        (a) A item such as \p{Yi}{3} in a lookbehind was not treated as fixed
156            length.
158        (b) An item such as \pL+ within a repeated group could cause crashes or
159            loops.
161        (c) A pattern such as \p{Yi}+(\P{Yi}+)(?1) could give an incorrect
162            "reference to non-existent subpattern" error.
164        (d) A pattern like (\P{Yi}{2}\277)? could loop at compile time.
166    24. A repeated \S or \W in UTF-8 mode could give wrong answers when multibyte
167        characters were involved (for example /\S{2}/8g with "A\x{a3}BC").
169    25. Using pcregrep in multiline, inverted mode (-Mv) caused it to loop.
171    26. Patterns such as [\P{Yi}A] which include \p or \P and just one other
172        character were causing crashes (broken optimization).
174    27. Patterns such as (\P{Yi}*\277)* (group with possible zero repeat containing
175        \p or \P) caused a compile-time loop.
177    28. More problems have arisen in unanchored patterns when CRLF is a valid line
178        break. For example, the unstudied pattern [\r\n]A does not match the string
179        "\r\nA" because change 7.0/46 below moves the current point on by two
180        characters after failing to match at the start. However, the pattern \nA
181        *does* match, because it doesn't start till \n, and if [\r\n]A is studied,
182        the same is true. There doesn't seem any very clean way out of this, but
183        what I have chosen to do makes the common cases work: PCRE now takes note
184        of whether there can be an explicit match for \r or \n anywhere in the
185        pattern, and if so, 7.0/46 no longer applies. As part of this change,
186        there's a new PCRE_INFO_HASCRORLF option for finding out whether a compiled
187        pattern has explicit CR or LF references.
189    29. Added (*CR) etc for changing newline setting at start of pattern.
192    Version 7.2 19-Jun-07
193    ---------------------
195     1. If the fr_FR locale cannot be found for test 3, try the "french" locale,
196        which is apparently normally available under Windows.
198     2. Re-jig the pcregrep tests with different newline settings in an attempt
199        to make them independent of the local environment's newline setting.
201     3. Add code to configure.ac to remove -g from the CFLAGS default settings.
203     4. Some of the "internals" tests were previously cut out when the link size
204        was not 2, because the output contained actual offsets. The recent new
205        "Z" feature of pcretest means that these can be cut out, making the tests
206        usable with all link sizes.
208     5. Implemented Stan Switzer's goto replacement for longjmp() when not using
209        stack recursion. This gives a massive performance boost under BSD, but just
210        a small improvement under Linux. However, it saves one field in the frame
211        in all cases.
213     6. Added more features from the forthcoming Perl 5.10:
215        (a) (?-n) (where n is a string of digits) is a relative subroutine or
216            recursion call. It refers to the nth most recently opened parentheses.
218        (b) (?+n) is also a relative subroutine call; it refers to the nth next
219            to be opened parentheses.
221        (c) Conditions that refer to capturing parentheses can be specified
222            relatively, for example, (?(-2)... or (?(+3)...
224        (d) \K resets the start of the current match so that everything before
225            is not part of it.
227        (e) \k{name} is synonymous with \k<name> and \k'name' (.NET compatible).
229        (f) \g{name} is another synonym - part of Perl 5.10's unification of
230            reference syntax.
232        (g) (?| introduces a group in which the numbering of parentheses in each
233            alternative starts with the same number.
235        (h) \h, \H, \v, and \V match horizontal and vertical whitespace.
237     7. Added two new calls to pcre_fullinfo(): PCRE_INFO_OKPARTIAL and
240     8. A pattern such as  (.*(.)?)*  caused pcre_exec() to fail by either not
241        terminating or by crashing. Diagnosed by Viktor Griph; it was in the code
242        for detecting groups that can match an empty string.
244     9. A pattern with a very large number of alternatives (more than several
245        hundred) was running out of internal workspace during the pre-compile
246        phase, where pcre_compile() figures out how much memory will be needed. A
247        bit of new cunning has reduced the workspace needed for groups with
248        alternatives. The 1000-alternative test pattern now uses 12 bytes of
249        workspace instead of running out of the 4096 that are available.
251    10. Inserted some missing (unsigned int) casts to get rid of compiler warnings.
253    11. Applied patch from Google to remove an optimization that didn't quite work.
254        The report of the bug said:
256          pcrecpp::RE("a*").FullMatch("aaa") matches, while
257          pcrecpp::RE("a*?").FullMatch("aaa") does not, and
258          pcrecpp::RE("a*?\\z").FullMatch("aaa") does again.
260    12. If \p or \P was used in non-UTF-8 mode on a character greater than 127
261        it matched the wrong number of bytes.
264    Version 7.1 24-Apr-07
265    ---------------------
267     1. Applied Bob Rossi and Daniel G's patches to convert the build system to one
268        that is more "standard", making use of automake and other Autotools. There
269        is some re-arrangement of the files and adjustment of comments consequent
270        on this.
272     2. Part of the patch fixed a problem with the pcregrep tests. The test of -r
273        for recursive directory scanning broke on some systems because the files
274        are not scanned in any specific order and on different systems the order
275        was different. A call to "sort" has been inserted into RunGrepTest for the
276        approprate test as a short-term fix. In the longer term there may be an
277        alternative.
279     3. I had an email from Eric Raymond about problems translating some of PCRE's
280        man pages to HTML (despite the fact that I distribute HTML pages, some
281        people do their own conversions for various reasons). The problems
282        concerned the use of low-level troff macros .br and .in. I have therefore
283        removed all such uses from the man pages (some were redundant, some could
284        be replaced by .nf/.fi pairs). The 132html script that I use to generate
285        HTML has been updated to handle .nf/.fi and to complain if it encounters
286        .br or .in.
288     4. Updated comments in configure.ac that get placed in config.h.in and also
289        arranged for config.h to be included in the distribution, with the name
290        config.h.generic, for the benefit of those who have to compile without
291        Autotools (compare pcre.h, which is now distributed as pcre.h.generic).
293     5. Updated the support (such as it is) for Virtual Pascal, thanks to Stefan
294        Weber: (1) pcre_internal.h was missing some function renames; (2) updated
295        makevp.bat for the current PCRE, using the additional files
296        makevp_c.txt, makevp_l.txt, and pcregexp.pas.
298     6. A Windows user reported a minor discrepancy with test 2, which turned out
299        to be caused by a trailing space on an input line that had got lost in his
300        copy. The trailing space was an accident, so I've just removed it.
302     7. Add -Wl,-R... flags in pcre-config.in for *BSD* systems, as I'm told
303        that is needed.
305     8. Mark ucp_table (in ucptable.h) and ucp_gentype (in pcre_ucp_searchfuncs.c)
306        as "const" (a) because they are and (b) because it helps the PHP
307        maintainers who have recently made a script to detect big data structures
308        in the php code that should be moved to the .rodata section. I remembered
309        to update Builducptable as well, so it won't revert if ucptable.h is ever
310        re-created.
312     9. Added some extra #ifdef SUPPORT_UTF8 conditionals into pcretest.c,
313        pcre_printint.src, pcre_compile.c, pcre_study.c, and pcre_tables.c, in
314        order to be able to cut out the UTF-8 tables in the latter when UTF-8
315        support is not required. This saves 1.5-2K of code, which is important in
316        some applications.
318        Later: more #ifdefs are needed in pcre_ord2utf8.c and pcre_valid_utf8.c
319        so as not to refer to the tables, even though these functions will never be
320        called when UTF-8 support is disabled. Otherwise there are problems with a
321        shared library.
323    10. Fixed two bugs in the emulated memmove() function in pcre_internal.h:
325        (a) It was defining its arguments as char * instead of void *.
327        (b) It was assuming that all moves were upwards in memory; this was true
328            a long time ago when I wrote it, but is no longer the case.
330        The emulated memove() is provided for those environments that have neither
331        memmove() nor bcopy(). I didn't think anyone used it these days, but that
332        is clearly not the case, as these two bugs were recently reported.
334    11. The script PrepareRelease is now distributed: it calls 132html, CleanTxt,
335        and Detrail to create the HTML documentation, the .txt form of the man
336        pages, and it removes trailing spaces from listed files. It also creates
337        pcre.h.generic and config.h.generic from pcre.h and config.h. In the latter
338        case, it wraps all the #defines with #ifndefs. This script should be run
339        before "make dist".
341    12. Fixed two fairly obscure bugs concerned with quantified caseless matching
342        with Unicode property support.
344        (a) For a maximizing quantifier, if the two different cases of the
345            character were of different lengths in their UTF-8 codings (there are
346            some cases like this - I found 11), and the matching function had to
347            back up over a mixture of the two cases, it incorrectly assumed they
348            were both the same length.
350        (b) When PCRE was configured to use the heap rather than the stack for
351            recursion during matching, it was not correctly preserving the data for
352            the other case of a UTF-8 character when checking ahead for a match
353            while processing a minimizing repeat. If the check also involved
354            matching a wide character, but failed, corruption could cause an
355            erroneous result when trying to check for a repeat of the original
356            character.
358    13. Some tidying changes to the testing mechanism:
360        (a) The RunTest script now detects the internal link size and whether there
361            is UTF-8 and UCP support by running ./pcretest -C instead of relying on
362            values substituted by "configure". (The RunGrepTest script already did
363            this for UTF-8.) The configure.ac script no longer substitutes the
364            relevant variables.
366        (b) The debugging options /B and /D in pcretest show the compiled bytecode
367            with length and offset values. This means that the output is different
368            for different internal link sizes. Test 2 is skipped for link sizes
369            other than 2 because of this, bypassing the problem. Unfortunately,
370            there was also a test in test 3 (the locale tests) that used /B and
371            failed for link sizes other than 2. Rather than cut the whole test out,
372            I have added a new /Z option to pcretest that replaces the length and
373            offset values with spaces. This is now used to make test 3 independent
374            of link size. (Test 2 will be tidied up later.)
376    14. If erroroffset was passed as NULL to pcre_compile, it provoked a
377        segmentation fault instead of returning the appropriate error message.
379    15. In multiline mode when the newline sequence was set to "any", the pattern
380        ^$ would give a match between the \r and \n of a subject such as "A\r\nB".
381        This doesn't seem right; it now treats the CRLF combination as the line
382        ending, and so does not match in that case. It's only a pattern such as ^$
383        that would hit this one: something like ^ABC$ would have failed after \r
384        and then tried again after \r\n.
386    16. Changed the comparison command for RunGrepTest from "diff -u" to "diff -ub"
387        in an attempt to make files that differ only in their line terminators
388        compare equal. This works on Linux.
390    17. Under certain error circumstances pcregrep might try to free random memory
391        as it exited. This is now fixed, thanks to valgrind.
393    19. In pcretest, if the pattern /(?m)^$/g<any> was matched against the string
394        "abc\r\n\r\n", it found an unwanted second match after the second \r. This
395        was because its rules for how to advance for /g after matching an empty
396        string at the end of a line did not allow for this case. They now check for
397        it specially.
399    20. pcretest is supposed to handle patterns and data of any length, by
400        extending its buffers when necessary. It was getting this wrong when the
401        buffer for a data line had to be extended.
403    21. Added PCRE_NEWLINE_ANYCRLF which is like ANY, but matches only CR, LF, or
404        CRLF as a newline sequence.
406    22. Code for handling Unicode properties in pcre_dfa_exec() wasn't being cut
407        out by #ifdef SUPPORT_UCP. This did no harm, as it could never be used, but
408        I have nevertheless tidied it up.
410    23. Added some casts to kill warnings from HP-UX ia64 compiler.
412    24. Added a man page for pcre-config.
415    Version 7.0 19-Dec-06
416    ---------------------
418     1. Fixed a signed/unsigned compiler warning in pcre_compile.c, shown up by
419        moving to gcc 4.1.1.
421     2. The -S option for pcretest uses setrlimit(); I had omitted to #include
422        sys/time.h, which is documented as needed for this function. It doesn't
423        seem to matter on Linux, but it showed up on some releases of OS X.
425     3. It seems that there are systems where bytes whose values are greater than
426        127 match isprint() in the "C" locale. The "C" locale should be the
427        default when a C program starts up. In most systems, only ASCII printing
428        characters match isprint(). This difference caused the output from pcretest
429        to vary, making some of the tests fail. I have changed pcretest so that:
431        (a) When it is outputting text in the compiled version of a pattern, bytes
432            other than 32-126 are always shown as hex escapes.
434        (b) When it is outputting text that is a matched part of a subject string,
435            it does the same, unless a different locale has been set for the match
436            (using the /L modifier). In this case, it uses isprint() to decide.
438     4. Fixed a major bug that caused incorrect computation of the amount of memory
439        required for a compiled pattern when options that changed within the
440        pattern affected the logic of the preliminary scan that determines the
441        length. The relevant options are -x, and -i in UTF-8 mode. The result was
442        that the computed length was too small. The symptoms of this bug were
443        either the PCRE error "internal error: code overflow" from pcre_compile(),
444        or a glibc crash with a message such as "pcretest: free(): invalid next
445        size (fast)". Examples of patterns that provoked this bug (shown in
446        pcretest format) are:
448          /(?-x: )/x
449          /(?x)(?-x: \s*#\s*)/
450          /((?i)[\x{c0}])/8
451          /(?i:[\x{c0}])/8
453        HOWEVER: Change 17 below makes this fix obsolete as the memory computation
454        is now done differently.
456     5. Applied patches from Google to: (a) add a QuoteMeta function to the C++
457        wrapper classes; (b) implement a new function in the C++ scanner that is
458        more efficient than the old way of doing things because it avoids levels of
459        recursion in the regex matching; (c) add a paragraph to the documentation
460        for the FullMatch() function.
462     6. The escape sequence \n was being treated as whatever was defined as
463        "newline". Not only was this contrary to the documentation, which states
464        that \n is character 10 (hex 0A), but it also went horribly wrong when
465        "newline" was defined as CRLF. This has been fixed.
467     7. In pcre_dfa_exec.c the value of an unsigned integer (the variable called c)
468        was being set to -1 for the "end of line" case (supposedly a value that no
469        character can have). Though this value is never used (the check for end of
470        line is "zero bytes in current character"), it caused compiler complaints.
471        I've changed it to 0xffffffff.
473     8. In pcre_version.c, the version string was being built by a sequence of
474        C macros that, in the event of PCRE_PRERELEASE being defined as an empty
475        string (as it is for production releases) called a macro with an empty
476        argument. The C standard says the result of this is undefined. The gcc
477        compiler treats it as an empty string (which was what was wanted) but it is
478        reported that Visual C gives an error. The source has been hacked around to
479        avoid this problem.
481     9. On the advice of a Windows user, included <io.h> and <fcntl.h> in Windows
482        builds of pcretest, and changed the call to _setmode() to use _O_BINARY
483        instead of 0x8000. Made all the #ifdefs test both _WIN32 and WIN32 (not all
484        of them did).
486    10. Originally, pcretest opened its input and output without "b"; then I was
487        told that "b" was needed in some environments, so it was added for release
488        5.0 to both the input and output. (It makes no difference on Unix-like
489        systems.) Later I was told that it is wrong for the input on Windows. I've
490        now abstracted the modes into two macros, to make it easier to fiddle with
491        them, and removed "b" from the input mode under Windows.
493    11. Added pkgconfig support for the C++ wrapper library, libpcrecpp.
495    12. Added -help and --help to pcretest as an official way of being reminded
496        of the options.
498    13. Removed some redundant semicolons after macro calls in pcrecpparg.h.in
499        and pcrecpp.cc because they annoy compilers at high warning levels.
501    14. A bit of tidying/refactoring in pcre_exec.c in the main bumpalong loop.
503    15. Fixed an occurrence of == in configure.ac that should have been = (shell
504        scripts are not C programs :-) and which was not noticed because it works
505        on Linux.
507    16. pcretest is supposed to handle any length of pattern and data line (as one
508        line or as a continued sequence of lines) by extending its input buffer if
509        necessary. This feature was broken for very long pattern lines, leading to
510        a string of junk being passed to pcre_compile() if the pattern was longer
511        than about 50K.
513    17. I have done a major re-factoring of the way pcre_compile() computes the
514        amount of memory needed for a compiled pattern. Previously, there was code
515        that made a preliminary scan of the pattern in order to do this. That was
516        OK when PCRE was new, but as the facilities have expanded, it has become
517        harder and harder to keep it in step with the real compile phase, and there
518        have been a number of bugs (see for example, 4 above). I have now found a
519        cunning way of running the real compile function in a "fake" mode that
520        enables it to compute how much memory it would need, while actually only
521        ever using a few hundred bytes of working memory and without too many
522        tests of the mode. This should make future maintenance and development
523        easier. A side effect of this work is that the limit of 200 on the nesting
524        depth of parentheses has been removed (though this was never a serious
525        limitation, I suspect). However, there is a downside: pcre_compile() now
526        runs more slowly than before (30% or more, depending on the pattern). I
527        hope this isn't a big issue. There is no effect on runtime performance.
529    18. Fixed a minor bug in pcretest: if a pattern line was not terminated by a
530        newline (only possible for the last line of a file) and it was a
531        pattern that set a locale (followed by /Lsomething), pcretest crashed.
533    19. Added additional timing features to pcretest. (1) The -tm option now times
534        matching only, not compiling. (2) Both -t and -tm can be followed, as a
535        separate command line item, by a number that specifies the number of
536        repeats to use when timing. The default is 50000; this gives better
537        precision, but takes uncomfortably long for very large patterns.
539    20. Extended pcre_study() to be more clever in cases where a branch of a
540        subpattern has no definite first character. For example, (a*|b*)[cd] would
541        previously give no result from pcre_study(). Now it recognizes that the
542        first character must be a, b, c, or d.
544    21. There was an incorrect error "recursive call could loop indefinitely" if
545        a subpattern (or the entire pattern) that was being tested for matching an
546        empty string contained only one non-empty item after a nested subpattern.
547        For example, the pattern (?>\x{100}*)\d(?R) provoked this error
548        incorrectly, because the \d was being skipped in the check.
550    22. The pcretest program now has a new pattern option /B and a command line
551        option -b, which is equivalent to adding /B to every pattern. This causes
552        it to show the compiled bytecode, without the additional information that
553        -d shows. The effect of -d is now the same as -b with -i (and similarly, /D
554        is the same as /B/I).
556    23. A new optimization is now able automatically to treat some sequences such
557        as a*b as a*+b. More specifically, if something simple (such as a character
558        or a simple class like \d) has an unlimited quantifier, and is followed by
559        something that cannot possibly match the quantified thing, the quantifier
560        is automatically "possessified".
562    24. A recursive reference to a subpattern whose number was greater than 39
563        went wrong under certain circumstances in UTF-8 mode. This bug could also
564        have affected the operation of pcre_study().
566    25. Realized that a little bit of performance could be had by replacing
567        (c & 0xc0) == 0xc0 with c >= 0xc0 when processing UTF-8 characters.
569    26. Timing data from pcretest is now shown to 4 decimal places instead of 3.
571    27. Possessive quantifiers such as a++ were previously implemented by turning
572        them into atomic groups such as ($>a+). Now they have their own opcodes,
573        which improves performance. This includes the automatically created ones
574        from 23 above.
576    28. A pattern such as (?=(\w+))\1: which simulates an atomic group using a
577        lookahead was broken if it was not anchored. PCRE was mistakenly expecting
578        the first matched character to be a colon. This applied both to named and
579        numbered groups.
581    29. The ucpinternal.h header file was missing its idempotency #ifdef.
583    30. I was sent a "project" file called libpcre.a.dev which I understand makes
584        building PCRE on Windows easier, so I have included it in the distribution.
586    31. There is now a check in pcretest against a ridiculously large number being
587        returned by pcre_exec() or pcre_dfa_exec(). If this happens in a /g or /G
588        loop, the loop is abandoned.
590    32. Forward references to subpatterns in conditions such as (?(2)...) where
591        subpattern 2 is defined later cause pcre_compile() to search forwards in
592        the pattern for the relevant set of parentheses. This search went wrong
593        when there were unescaped parentheses in a character class, parentheses
594        escaped with \Q...\E, or parentheses in a #-comment in /x mode.
596    33. "Subroutine" calls and backreferences were previously restricted to
597        referencing subpatterns earlier in the regex. This restriction has now
598        been removed.
600    34. Added a number of extra features that are going to be in Perl 5.10. On the
601        whole, these are just syntactic alternatives for features that PCRE had
602        previously implemented using the Python syntax or my own invention. The
603        other formats are all retained for compatibility.
605        (a) Named groups can now be defined as (?<name>...) or (?'name'...) as well
606            as (?P<name>...). The new forms, as well as being in Perl 5.10, are
607            also .NET compatible.
609        (b) A recursion or subroutine call to a named group can now be defined as
610            (?&name) as well as (?P>name).
612        (c) A backreference to a named group can now be defined as \k<name> or
613            \k'name' as well as (?P=name). The new forms, as well as being in Perl
614            5.10, are also .NET compatible.
616        (d) A conditional reference to a named group can now use the syntax
617            (?(<name>) or (?('name') as well as (?(name).
619        (e) A "conditional group" of the form (?(DEFINE)...) can be used to define
620            groups (named and numbered) that are never evaluated inline, but can be
621            called as "subroutines" from elsewhere. In effect, the DEFINE condition
622            is always false. There may be only one alternative in such a group.
624        (f) A test for recursion can be given as (?(R1).. or (?(R&name)... as well
625            as the simple (?(R). The condition is true only if the most recent
626            recursion is that of the given number or name. It does not search out
627            through the entire recursion stack.
629        (g) The escape \gN or \g{N} has been added, where N is a positive or
630            negative number, specifying an absolute or relative reference.
632    35. Tidied to get rid of some further signed/unsigned compiler warnings and
633        some "unreachable code" warnings.
635    36. Updated the Unicode property tables to Unicode version 5.0.0. Amongst other
636        things, this adds five new scripts.
638    37. Perl ignores orphaned \E escapes completely. PCRE now does the same.
639        There were also incompatibilities regarding the handling of \Q..\E inside
640        character classes, for example with patterns like [\Qa\E-\Qz\E] where the
641        hyphen was adjacent to \Q or \E. I hope I've cleared all this up now.
643    38. Like Perl, PCRE detects when an indefinitely repeated parenthesized group
644        matches an empty string, and forcibly breaks the loop. There were bugs in
645        this code in non-simple cases. For a pattern such as  ^(a()*)*  matched
646        against  aaaa  the result was just "a" rather than "aaaa", for example. Two
647        separate and independent bugs (that affected different cases) have been
648        fixed.
650    39. Refactored the code to abolish the use of different opcodes for small
651        capturing bracket numbers. This is a tidy that I avoided doing when I
652        removed the limit on the number of capturing brackets for 3.5 back in 2001.
653        The new approach is not only tidier, it makes it possible to reduce the
654        memory needed to fix the previous bug (38).
656    40. Implemented PCRE_NEWLINE_ANY to recognize any of the Unicode newline
657        sequences (http://unicode.org/unicode/reports/tr18/) as "newline" when
658        processing dot, circumflex, or dollar metacharacters, or #-comments in /x
659        mode.
661    41. Add \R to match any Unicode newline sequence, as suggested in the Unicode
662        report.
664    42. Applied patch, originally from Ari Pollak, modified by Google, to allow
665        copy construction and assignment in the C++ wrapper.
667    43. Updated pcregrep to support "--newline=any". In the process, I fixed a
668        couple of bugs that could have given wrong results in the "--newline=crlf"
669        case.
671    44. Added a number of casts and did some reorganization of signed/unsigned int
672        variables following suggestions from Dair Grant. Also renamed the variable
673        "this" as "item" because it is a C++ keyword.
675    45. Arranged for dftables to add
677          #include "pcre_internal.h"
679        to pcre_chartables.c because without it, gcc 4.x may remove the array
680        definition from the final binary if PCRE is built into a static library and
681        dead code stripping is activated.
683    46. For an unanchored pattern, if a match attempt fails at the start of a
684        newline sequence, and the newline setting is CRLF or ANY, and the next two
685        characters are CRLF, advance by two characters instead of one.
688  Version 6.7 04-Jul-06  Version 6.7 04-Jul-06
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