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Sat Feb 24 21:40:54 2007 UTC (14 years, 1 month ago) by nigel
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Tag code/trunk as code/tags/pcre-6.1.
1 ChangeLog for PCRE
2 ------------------
4 Version 6.1 21-Jun-05
5 ---------------------
7 1. There was one reference to the variable "posix" in pcretest.c that was not
8 surrounded by "#if !defined NOPOSIX".
10 2. Make it possible to compile pcretest without DFA support, UTF8 support, or
11 the cross-check on the old pcre_info() function, for the benefit of the
12 cut-down version of PCRE that is currently imported into Exim.
14 3. A (silly) pattern starting with (?i)(?-i) caused an internal space
15 allocation error. I've done the easy fix, which wastes 2 bytes for sensible
16 patterns that start (?i) but I don't think that matters. The use of (?i) is
17 just an example; this all applies to the other options as well.
19 4. Since libtool seems to echo the compile commands it is issuing, the output
20 from "make" can be reduced a bit by putting "@" in front of each libtool
21 compile command.
23 5. Patch from the folks at Google for configure.in to be a bit more thorough
24 in checking for a suitable C++ installation before trying to compile the
25 C++ stuff. This should fix a reported problem when a compiler was present,
26 but no suitable headers.
28 6. The man pages all had just "PCRE" as their title. I have changed them to
29 be the relevant file name. I have also arranged that these names are
30 retained in the file doc/pcre.txt, which is a concatenation in text format
31 of all the man pages except the little individual ones for each function.
33 7. The NON-UNIX-USE file had not been updated for the different set of source
34 files that come with release 6. I also added a few comments about the C++
35 wrapper.
38 Version 6.0 07-Jun-05
39 ---------------------
41 1. Some minor internal re-organization to help with my DFA experiments.
43 2. Some missing #ifdef SUPPORT_UCP conditionals in pcretest and printint that
44 didn't matter for the library itself when fully configured, but did matter
45 when compiling without UCP support, or within Exim, where the ucp files are
46 not imported.
48 3. Refactoring of the library code to split up the various functions into
49 different source modules. The addition of the new DFA matching code (see
50 below) to a single monolithic source would have made it really too
51 unwieldy, quite apart from causing all the code to be include in a
52 statically linked application, when only some functions are used. This is
53 relevant even without the DFA addition now that patterns can be compiled in
54 one application and matched in another.
56 The downside of splitting up is that there have to be some external
57 functions and data tables that are used internally in different modules of
58 the library but which are not part of the API. These have all had their
59 names changed to start with "_pcre_" so that they are unlikely to clash
60 with other external names.
62 4. Added an alternate matching function, pcre_dfa_exec(), which matches using
63 a different (DFA) algorithm. Although it is slower than the original
64 function, it does have some advantages for certain types of matching
65 problem.
67 5. Upgrades to pcretest in order to test the features of pcre_dfa_exec(),
68 including restarting after a partial match.
70 6. A patch for pcregrep that defines INVALID_FILE_ATTRIBUTES if it is not
71 defined when compiling for Windows was sent to me. I have put it into the
72 code, though I have no means of testing or verifying it.
74 7. Added the pcre_refcount() auxiliary function.
76 8. Added the PCRE_FIRSTLINE option. This constrains an unanchored pattern to
77 match before or at the first newline in the subject string. In pcretest,
78 the /f option on a pattern can be used to set this.
80 9. A repeated \w when used in UTF-8 mode with characters greater than 256
81 would behave wrongly. This has been present in PCRE since release 4.0.
83 10. A number of changes to the pcregrep command:
85 (a) Refactored how -x works; insert ^(...)$ instead of setting
86 PCRE_ANCHORED and checking the length, in preparation for adding
87 something similar for -w.
89 (b) Added the -w (match as a word) option.
91 (c) Refactored the way lines are read and buffered so as to have more
92 than one at a time available.
94 (d) Implemented a pcregrep test script.
96 (e) Added the -M (multiline match) option. This allows patterns to match
97 over several lines of the subject. The buffering ensures that at least
98 8K, or the rest of the document (whichever is the shorter) is available
99 for matching (and similarly the previous 8K for lookbehind assertions).
101 (f) Changed the --help output so that it now says
103 -w, --word-regex(p)
105 instead of two lines, one with "regex" and the other with "regexp"
106 because that confused at least one person since the short forms are the
107 same. (This required a bit of code, as the output is generated
108 automatically from a table. It wasn't just a text change.)
110 (g) -- can be used to terminate pcregrep options if the next thing isn't an
111 option but starts with a hyphen. Could be a pattern or a path name
112 starting with a hyphen, for instance.
114 (h) "-" can be given as a file name to represent stdin.
116 (i) When file names are being printed, "(standard input)" is used for
117 the standard input, for compatibility with GNU grep. Previously
118 "<stdin>" was used.
120 (j) The option --label=xxx can be used to supply a name to be used for
121 stdin when file names are being printed. There is no short form.
123 (k) Re-factored the options decoding logic because we are going to add
124 two more options that take data. Such options can now be given in four
125 different ways, e.g. "-fname", "-f name", "--file=name", "--file name".
127 (l) Added the -A, -B, and -C options for requesting that lines of context
128 around matches be printed.
130 (m) Added the -L option to print the names of files that do not contain
131 any matching lines, that is, the complement of -l.
133 (n) The return code is 2 if any file cannot be opened, but pcregrep does
134 continue to scan other files.
136 (o) The -s option was incorrectly implemented. For compatibility with other
137 greps, it now suppresses the error message for a non-existent or non-
138 accessible file (but not the return code). There is a new option called
139 -q that suppresses the output of matching lines, which was what -s was
140 previously doing.
142 (p) Added --include and --exclude options to specify files for inclusion
143 and exclusion when recursing.
145 11. The Makefile was not using the Autoconf-supported LDFLAGS macro properly.
146 Hopefully, it now does.
148 12. Missing cast in pcre_study().
150 13. Added an "uninstall" target to the makefile.
152 14. Replaced "extern" in the function prototypes in Makefile.in with
153 "PCRE_DATA_SCOPE", which defaults to 'extern' or 'extern "C"' in the Unix
154 world, but is set differently for Windows.
156 15. Added a second compiling function called pcre_compile2(). The only
157 difference is that it has an extra argument, which is a pointer to an
158 integer error code. When there is a compile-time failure, this is set
159 non-zero, in addition to the error test pointer being set to point to an
160 error message. The new argument may be NULL if no error number is required
161 (but then you may as well call pcre_compile(), which is now just a
162 wrapper). This facility is provided because some applications need a
163 numeric error indication, but it has also enabled me to tidy up the way
164 compile-time errors are handled in the POSIX wrapper.
166 16. Added VPATH=.libs to the makefile; this should help when building with one
167 prefix path and installing with another. (Or so I'm told by someone who
168 knows more about this stuff than I do.)
170 17. Added a new option, REG_DOTALL, to the POSIX function regcomp(). This
171 passes PCRE_DOTALL to the pcre_compile() function, making the "." character
172 match everything, including newlines. This is not POSIX-compatible, but
173 somebody wanted the feature. From pcretest it can be activated by using
174 both the P and the s flags.
176 18. AC_PROG_LIBTOOL appeared twice in Makefile.in. Removed one.
178 19. libpcre.pc was being incorrectly installed as executable.
180 20. A couple of places in pcretest check for end-of-line by looking for '\n';
181 it now also looks for '\r' so that it will work unmodified on Windows.
183 21. Added Google's contributed C++ wrapper to the distribution.
185 22. Added some untidy missing memory free() calls in pcretest, to keep
186 Electric Fence happy when testing.
190 Version 5.0 13-Sep-04
191 ---------------------
193 1. Internal change: literal characters are no longer packed up into items
194 containing multiple characters in a single byte-string. Each character
195 is now matched using a separate opcode. However, there may be more than one
196 byte in the character in UTF-8 mode.
198 2. The pcre_callout_block structure has two new fields: pattern_position and
199 next_item_length. These contain the offset in the pattern to the next match
200 item, and its length, respectively.
202 3. The PCRE_AUTO_CALLOUT option for pcre_compile() requests the automatic
203 insertion of callouts before each pattern item. Added the /C option to
204 pcretest to make use of this.
206 4. On the advice of a Windows user, the lines
208 #if defined(_WIN32) || defined(WIN32)
209 _setmode( _fileno( stdout ), 0x8000 );
210 #endif /* defined(_WIN32) || defined(WIN32) */
212 have been added to the source of pcretest. This apparently does useful
213 magic in relation to line terminators.
215 5. Changed "r" and "w" in the calls to fopen() in pcretest to "rb" and "wb"
216 for the benefit of those environments where the "b" makes a difference.
218 6. The icc compiler has the same options as gcc, but "configure" doesn't seem
219 to know about it. I have put a hack into configure.in that adds in code
220 to set GCC=yes if CC=icc. This seems to end up at a point in the
221 generated configure script that is early enough to affect the setting of
222 compiler options, which is what is needed, but I have no means of testing
223 whether it really works. (The user who reported this had patched the
224 generated configure script, which of course I cannot do.)
226 LATER: After change 22 below (new libtool files), the configure script
227 seems to know about icc (and also ecc). Therefore, I have commented out
228 this hack in configure.in.
230 7. Added support for pkg-config (2 patches were sent in).
232 8. Negated POSIX character classes that used a combination of internal tables
233 were completely broken. These were [[:^alpha:]], [[:^alnum:]], and
234 [[:^ascii]]. Typically, they would match almost any characters. The other
235 POSIX classes were not broken in this way.
237 9. Matching the pattern "\b.*?" against "ab cd", starting at offset 1, failed
238 to find the match, as PCRE was deluded into thinking that the match had to
239 start at the start point or following a newline. The same bug applied to
240 patterns with negative forward assertions or any backward assertions
241 preceding ".*" at the start, unless the pattern required a fixed first
242 character. This was a failing pattern: "(?!.bcd).*". The bug is now fixed.
244 10. In UTF-8 mode, when moving forwards in the subject after a failed match
245 starting at the last subject character, bytes beyond the end of the subject
246 string were read.
248 11. Renamed the variable "class" as "classbits" to make life easier for C++
249 users. (Previously there was a macro definition, but it apparently wasn't
250 enough.)
252 12. Added the new field "tables" to the extra data so that tables can be passed
253 in at exec time, or the internal tables can be re-selected. This allows
254 a compiled regex to be saved and re-used at a later time by a different
255 program that might have everything at different addresses.
257 13. Modified the pcre-config script so that, when run on Solaris, it shows a
258 -R library as well as a -L library.
260 14. The debugging options of pcretest (-d on the command line or D on a
261 pattern) showed incorrect output for anything following an extended class
262 that contained multibyte characters and which was followed by a quantifier.
264 15. Added optional support for general category Unicode character properties
265 via the \p, \P, and \X escapes. Unicode property support implies UTF-8
266 support. It adds about 90K to the size of the library. The meanings of the
267 inbuilt class escapes such as \d and \s have NOT been changed.
269 16. Updated pcredemo.c to include calls to free() to release the memory for the
270 compiled pattern.
272 17. The generated file chartables.c was being created in the source directory
273 instead of in the building directory. This caused the build to fail if the
274 source directory was different from the building directory, and was
275 read-only.
277 18. Added some sample Win commands from Mark Tetrode into the NON-UNIX-USE
278 file. No doubt somebody will tell me if they don't make sense... Also added
279 Dan Mooney's comments about building on OpenVMS.
281 19. Added support for partial matching via the PCRE_PARTIAL option for
282 pcre_exec() and the \P data escape in pcretest.
284 20. Extended pcretest with 3 new pattern features:
286 (i) A pattern option of the form ">rest-of-line" causes pcretest to
287 write the compiled pattern to the file whose name is "rest-of-line".
288 This is a straight binary dump of the data, with the saved pointer to
289 the character tables forced to be NULL. The study data, if any, is
290 written too. After writing, pcretest reads a new pattern.
292 (ii) If, instead of a pattern, "<rest-of-line" is given, pcretest reads a
293 compiled pattern from the given file. There must not be any
294 occurrences of "<" in the file name (pretty unlikely); if there are,
295 pcretest will instead treat the initial "<" as a pattern delimiter.
296 After reading in the pattern, pcretest goes on to read data lines as
297 usual.
299 (iii) The F pattern option causes pcretest to flip the bytes in the 32-bit
300 and 16-bit fields in a compiled pattern, to simulate a pattern that
301 was compiled on a host of opposite endianness.
303 21. The pcre-exec() function can now cope with patterns that were compiled on
304 hosts of opposite endianness, with this restriction:
306 As for any compiled expression that is saved and used later, the tables
307 pointer field cannot be preserved; the extra_data field in the arguments
308 to pcre_exec() should be used to pass in a tables address if a value
309 other than the default internal tables were used at compile time.
311 22. Calling pcre_exec() with a negative value of the "ovecsize" parameter is
312 now diagnosed as an error. Previously, most of the time, a negative number
313 would have been treated as zero, but if in addition "ovector" was passed as
314 NULL, a crash could occur.
316 23. Updated the files ltmain.sh, config.sub, config.guess, and aclocal.m4 with
317 new versions from the libtool 1.5 distribution (the last one is a copy of
318 a file called libtool.m4). This seems to have fixed the need to patch
319 "configure" to support Darwin 1.3 (which I used to do). However, I still
320 had to patch ltmain.sh to ensure that ${SED} is set (it isn't on my
321 workstation).
323 24. Changed the PCRE licence to be the more standard "BSD" licence.
326 Version 4.5 01-Dec-03
327 ---------------------
329 1. There has been some re-arrangement of the code for the match() function so
330 that it can be compiled in a version that does not call itself recursively.
331 Instead, it keeps those local variables that need separate instances for
332 each "recursion" in a frame on the heap, and gets/frees frames whenever it
333 needs to "recurse". Keeping track of where control must go is done by means
334 of setjmp/longjmp. The whole thing is implemented by a set of macros that
335 hide most of the details from the main code, and operates only if
336 NO_RECURSE is defined while compiling pcre.c. If PCRE is built using the
337 "configure" mechanism, "--disable-stack-for-recursion" turns on this way of
338 operating.
340 To make it easier for callers to provide specially tailored get/free
341 functions for this usage, two new functions, pcre_stack_malloc, and
342 pcre_stack_free, are used. They are always called in strict stacking order,
343 and the size of block requested is always the same.
345 The PCRE_CONFIG_STACKRECURSE info parameter can be used to find out whether
346 PCRE has been compiled to use the stack or the heap for recursion. The
347 -C option of pcretest uses this to show which version is compiled.
349 A new data escape \S, is added to pcretest; it causes the amounts of store
350 obtained and freed by both kinds of malloc/free at match time to be added
351 to the output.
353 2. Changed the locale test to use "fr_FR" instead of "fr" because that's
354 what's available on my current Linux desktop machine.
356 3. When matching a UTF-8 string, the test for a valid string at the start has
357 been extended. If start_offset is not zero, PCRE now checks that it points
358 to a byte that is the start of a UTF-8 character. If not, it returns
359 PCRE_ERROR_BADUTF8_OFFSET (-11). Note: the whole string is still checked;
360 this is necessary because there may be backward assertions in the pattern.
361 When matching the same subject several times, it may save resources to use
362 PCRE_NO_UTF8_CHECK on all but the first call if the string is long.
364 4. The code for checking the validity of UTF-8 strings has been tightened so
365 that it rejects (a) strings containing 0xfe or 0xff bytes and (b) strings
366 containing "overlong sequences".
368 5. Fixed a bug (appearing twice) that I could not find any way of exploiting!
369 I had written "if ((digitab[*p++] && chtab_digit) == 0)" where the "&&"
370 should have been "&", but it just so happened that all the cases this let
371 through by mistake were picked up later in the function.
373 6. I had used a variable called "isblank" - this is a C99 function, causing
374 some compilers to warn. To avoid this, I renamed it (as "blankclass").
376 7. Cosmetic: (a) only output another newline at the end of pcretest if it is
377 prompting; (b) run "./pcretest /dev/null" at the start of the test script
378 so the version is shown; (c) stop "make test" echoing "./RunTest".
380 8. Added patches from David Burgess to enable PCRE to run on EBCDIC systems.
382 9. The prototype for memmove() for systems that don't have it was using
383 size_t, but the inclusion of the header that defines size_t was later. I've
384 moved the #includes for the C headers earlier to avoid this.
386 10. Added some adjustments to the code to make it easier to compiler on certain
387 special systems:
389 (a) Some "const" qualifiers were missing.
390 (b) Added the macro EXPORT before all exported functions; by default this
391 is defined to be empty.
392 (c) Changed the dftables auxiliary program (that builds chartables.c) so
393 that it reads its output file name as an argument instead of writing
394 to the standard output and assuming this can be redirected.
396 11. In UTF-8 mode, if a recursive reference (e.g. (?1)) followed a character
397 class containing characters with values greater than 255, PCRE compilation
398 went into a loop.
400 12. A recursive reference to a subpattern that was within another subpattern
401 that had a minimum quantifier of zero caused PCRE to crash. For example,
402 (x(y(?2))z)? provoked this bug with a subject that got as far as the
403 recursion. If the recursively-called subpattern itself had a zero repeat,
404 that was OK.
406 13. In pcretest, the buffer for reading a data line was set at 30K, but the
407 buffer into which it was copied (for escape processing) was still set at
408 1024, so long lines caused crashes.
410 14. A pattern such as /[ab]{1,3}+/ failed to compile, giving the error
411 "internal error: code overflow...". This applied to any character class
412 that was followed by a possessive quantifier.
414 15. Modified the Makefile to add libpcre.la as a prerequisite for
415 libpcreposix.la because I was told this is needed for a parallel build to
416 work.
418 16. If a pattern that contained .* following optional items at the start was
419 studied, the wrong optimizing data was generated, leading to matching
420 errors. For example, studying /[ab]*.*c/ concluded, erroneously, that any
421 matching string must start with a or b or c. The correct conclusion for
422 this pattern is that a match can start with any character.
425 Version 4.4 13-Aug-03
426 ---------------------
428 1. In UTF-8 mode, a character class containing characters with values between
429 127 and 255 was not handled correctly if the compiled pattern was studied.
430 In fixing this, I have also improved the studying algorithm for such
431 classes (slightly).
433 2. Three internal functions had redundant arguments passed to them. Removal
434 might give a very teeny performance improvement.
436 3. Documentation bug: the value of the capture_top field in a callout is *one
437 more than* the number of the hightest numbered captured substring.
439 4. The Makefile linked pcretest and pcregrep with -lpcre, which could result
440 in incorrectly linking with a previously installed version. They now link
441 explicitly with libpcre.la.
443 5. configure.in no longer needs to recognize Cygwin specially.
445 6. A problem in pcre.in for Windows platforms is fixed.
447 7. If a pattern was successfully studied, and the -d (or /D) flag was given to
448 pcretest, it used to include the size of the study block as part of its
449 output. Unfortunately, the structure contains a field that has a different
450 size on different hardware architectures. This meant that the tests that
451 showed this size failed. As the block is currently always of a fixed size,
452 this information isn't actually particularly useful in pcretest output, so
453 I have just removed it.
455 8. Three pre-processor statements accidentally did not start in column 1.
456 Sadly, there are *still* compilers around that complain, even though
457 standard C has not required this for well over a decade. Sigh.
459 9. In pcretest, the code for checking callouts passed small integers in the
460 callout_data field, which is a void * field. However, some picky compilers
461 complained about the casts involved for this on 64-bit systems. Now
462 pcretest passes the address of the small integer instead, which should get
463 rid of the warnings.
465 10. By default, when in UTF-8 mode, PCRE now checks for valid UTF-8 strings at
466 both compile and run time, and gives an error if an invalid UTF-8 sequence
467 is found. There is a option for disabling this check in cases where the
468 string is known to be correct and/or the maximum performance is wanted.
470 11. In response to a bug report, I changed one line in Makefile.in from
472 -Wl,--out-implib,.libs/lib@WIN_PREFIX@pcreposix.dll.a \
473 to
474 -Wl,--out-implib,.libs/@WIN_PREFIX@libpcreposix.dll.a \
476 to look similar to other lines, but I have no way of telling whether this
477 is the right thing to do, as I do not use Windows. No doubt I'll get told
478 if it's wrong...
481 Version 4.3 21-May-03
482 ---------------------
484 1. Two instances of @WIN_PREFIX@ omitted from the Windows targets in the
485 Makefile.
487 2. Some refactoring to improve the quality of the code:
489 (i) The utf8_table... variables are now declared "const".
491 (ii) The code for \cx, which used the "case flipping" table to upper case
492 lower case letters, now just substracts 32. This is ASCII-specific,
493 but the whole concept of \cx is ASCII-specific, so it seems
494 reasonable.
496 (iii) PCRE was using its character types table to recognize decimal and
497 hexadecimal digits in the pattern. This is silly, because it handles
498 only 0-9, a-f, and A-F, but the character types table is locale-
499 specific, which means strange things might happen. A private
500 table is now used for this - though it costs 256 bytes, a table is
501 much faster than multiple explicit tests. Of course, the standard
502 character types table is still used for matching digits in subject
503 strings against \d.
505 (iv) Strictly, the identifier ESC_t is reserved by POSIX (all identifiers
506 ending in _t are). So I've renamed it as ESC_tee.
508 3. The first argument for regexec() in the POSIX wrapper should have been
509 defined as "const".
511 4. Changed pcretest to use malloc() for its buffers so that they can be
512 Electric Fenced for debugging.
514 5. There were several places in the code where, in UTF-8 mode, PCRE would try
515 to read one or more bytes before the start of the subject string. Often this
516 had no effect on PCRE's behaviour, but in some circumstances it could
517 provoke a segmentation fault.
519 6. A lookbehind at the start of a pattern in UTF-8 mode could also cause PCRE
520 to try to read one or more bytes before the start of the subject string.
522 7. A lookbehind in a pattern matched in non-UTF-8 mode on a PCRE compiled with
523 UTF-8 support could misbehave in various ways if the subject string
524 contained bytes with the 0x80 bit set and the 0x40 bit unset in a lookbehind
525 area. (PCRE was not checking for the UTF-8 mode flag, and trying to move
526 back over UTF-8 characters.)
529 Version 4.2 14-Apr-03
530 ---------------------
532 1. Typo "#if SUPPORT_UTF8" instead of "#ifdef SUPPORT_UTF8" fixed.
534 2. Changes to the building process, supplied by Ronald Landheer-Cieslak
535 [ON_WINDOWS]: new variable, "#" on non-Windows platforms
536 [NOT_ON_WINDOWS]: new variable, "#" on Windows platforms
537 [WIN_PREFIX]: new variable, "cyg" for Cygwin
538 * Makefile.in: use autoconf substitution for OBJEXT, EXEEXT, BUILD_OBJEXT
540 Note: automatic setting of the BUILD variables is not yet working
541 set CPPFLAGS and BUILD_CPPFLAGS (but don't use yet) - should be used at
542 compile-time but not at link-time
543 [LINK]: use for linking executables only
544 make different versions for Windows and non-Windows
545 [LINKLIB]: new variable, copy of UNIX-style LINK, used for linking
546 libraries
547 [LINK_FOR_BUILD]: new variable
548 [OBJEXT]: use throughout
549 [EXEEXT]: use throughout
550 <winshared>: new target
551 <wininstall>: new target
552 <dftables.o>: use native compiler
553 <dftables>: use native linker
554 <install>: handle Windows platform correctly
555 <clean>: ditto
556 <check>: ditto
557 copy DLL to top builddir before testing
559 As part of these changes, -no-undefined was removed again. This was reported
560 to give trouble on HP-UX 11.0, so getting rid of it seems like a good idea
561 in any case.
563 3. Some tidies to get rid of compiler warnings:
565 . In the match_data structure, match_limit was an unsigned long int, whereas
566 match_call_count was an int. I've made them both unsigned long ints.
568 . In pcretest the fact that a const uschar * doesn't automatically cast to
569 a void * provoked a warning.
571 . Turning on some more compiler warnings threw up some "shadow" variables
572 and a few more missing casts.
574 4. If PCRE was complied with UTF-8 support, but called without the PCRE_UTF8
575 option, a class that contained a single character with a value between 128
576 and 255 (e.g. /[\xFF]/) caused PCRE to crash.
578 5. If PCRE was compiled with UTF-8 support, but called without the PCRE_UTF8
579 option, a class that contained several characters, but with at least one
580 whose value was between 128 and 255 caused PCRE to crash.
583 Version 4.1 12-Mar-03
584 ---------------------
586 1. Compiling with gcc -pedantic found a couple of places where casts were
587 needed, and a string in dftables.c that was longer than standard compilers are
588 required to support.
590 2. Compiling with Sun's compiler found a few more places where the code could
591 be tidied up in order to avoid warnings.
593 3. The variables for cross-compiling were called HOST_CC and HOST_CFLAGS; the
594 first of these names is deprecated in the latest Autoconf in favour of the name
595 CC_FOR_BUILD, because "host" is typically used to mean the system on which the
596 compiled code will be run. I can't find a reference for HOST_CFLAGS, but by
597 analogy I have changed it to CFLAGS_FOR_BUILD.
599 4. Added -no-undefined to the linking command in the Makefile, because this is
600 apparently helpful for Windows. To make it work, also added "-L. -lpcre" to the
601 linking step for the pcreposix library.
603 5. PCRE was failing to diagnose the case of two named groups with the same
604 name.
606 6. A problem with one of PCRE's optimizations was discovered. PCRE remembers a
607 literal character that is needed in the subject for a match, and scans along to
608 ensure that it is present before embarking on the full matching process. This
609 saves time in cases of nested unlimited repeats that are never going to match.
610 Problem: the scan can take a lot of time if the subject is very long (e.g.
611 megabytes), thus penalizing straightforward matches. It is now done only if the
612 amount of subject to be scanned is less than 1000 bytes.
614 7. A lesser problem with the same optimization is that it was recording the
615 first character of an anchored pattern as "needed", thus provoking a search
616 right along the subject, even when the first match of the pattern was going to
617 fail. The "needed" character is now not set for anchored patterns, unless it
618 follows something in the pattern that is of non-fixed length. Thus, it still
619 fulfils its original purpose of finding quick non-matches in cases of nested
620 unlimited repeats, but isn't used for simple anchored patterns such as /^abc/.
623 Version 4.0 17-Feb-03
624 ---------------------
626 1. If a comment in an extended regex that started immediately after a meta-item
627 extended to the end of string, PCRE compiled incorrect data. This could lead to
628 all kinds of weird effects. Example: /#/ was bad; /()#/ was bad; /a#/ was not.
630 2. Moved to autoconf 2.53 and libtool 1.4.2.
632 3. Perl 5.8 no longer needs "use utf8" for doing UTF-8 things. Consequently,
633 the special perltest8 script is no longer needed - all the tests can be run
634 from a single perltest script.
636 4. From 5.004, Perl has not included the VT character (0x0b) in the set defined
637 by \s. It has now been removed in PCRE. This means it isn't recognized as
638 whitespace in /x regexes too, which is the same as Perl. Note that the POSIX
639 class [:space:] *does* include VT, thereby creating a mess.
641 5. Added the class [:blank:] (a GNU extension from Perl 5.8) to match only
642 space and tab.
644 6. Perl 5.005 was a long time ago. It's time to amalgamate the tests that use
645 its new features into the main test script, reducing the number of scripts.
647 7. Perl 5.8 has changed the meaning of patterns like /a(?i)b/. Earlier versions
648 were backward compatible, and made the (?i) apply to the whole pattern, as if
649 /i were given. Now it behaves more logically, and applies the option setting
650 only to what follows. PCRE has been changed to follow suit. However, if it
651 finds options settings right at the start of the pattern, it extracts them into
652 the global options, as before. Thus, they show up in the info data.
654 8. Added support for the \Q...\E escape sequence. Characters in between are
655 treated as literals. This is slightly different from Perl in that $ and @ are
656 also handled as literals inside the quotes. In Perl, they will cause variable
657 interpolation. Note the following examples:
659 Pattern PCRE matches Perl matches
661 \Qabc$xyz\E abc$xyz abc followed by the contents of $xyz
662 \Qabc\$xyz\E abc\$xyz abc\$xyz
663 \Qabc\E\$\Qxyz\E abc$xyz abc$xyz
665 For compatibility with Perl, \Q...\E sequences are recognized inside character
666 classes as well as outside them.
668 9. Re-organized 3 code statements in pcretest to avoid "overflow in
669 floating-point constant arithmetic" warnings from a Microsoft compiler. Added a
670 (size_t) cast to one statement in pcretest and one in pcreposix to avoid
671 signed/unsigned warnings.
673 10. SunOS4 doesn't have strtoul(). This was used only for unpicking the -o
674 option for pcretest, so I've replaced it by a simple function that does just
675 that job.
677 11. pcregrep was ending with code 0 instead of 2 for the commands "pcregrep" or
678 "pcregrep -".
680 12. Added "possessive quantifiers" ?+, *+, ++, and {,}+ which come from Sun's
681 Java package. This provides some syntactic sugar for simple cases of what my
682 documentation calls "once-only subpatterns". A pattern such as x*+ is the same
683 as (?>x*). In other words, if what is inside (?>...) is just a single repeated
684 item, you can use this simplified notation. Note that only makes sense with
685 greedy quantifiers. Consequently, the use of the possessive quantifier forces
686 greediness, whatever the setting of the PCRE_UNGREEDY option.
688 13. A change of greediness default within a pattern was not taking effect at
689 the current level for patterns like /(b+(?U)a+)/. It did apply to parenthesized
690 subpatterns that followed. Patterns like /b+(?U)a+/ worked because the option
691 was abstracted outside.
693 14. PCRE now supports the \G assertion. It is true when the current matching
694 position is at the start point of the match. This differs from \A when the
695 starting offset is non-zero. Used with the /g option of pcretest (or similar
696 code), it works in the same way as it does for Perl's /g option. If all
697 alternatives of a regex begin with \G, the expression is anchored to the start
698 match position, and the "anchored" flag is set in the compiled expression.
700 15. Some bugs concerning the handling of certain option changes within patterns
701 have been fixed. These applied to options other than (?ims). For example,
702 "a(?x: b c )d" did not match "XabcdY" but did match "Xa b c dY". It should have
703 been the other way round. Some of this was related to change 7 above.
705 16. PCRE now gives errors for /[.x.]/ and /[=x=]/ as unsupported POSIX
706 features, as Perl does. Previously, PCRE gave the warnings only for /[[.x.]]/
707 and /[[=x=]]/. PCRE now also gives an error for /[:name:]/ because it supports
708 POSIX classes only within a class (e.g. /[[:alpha:]]/).
710 17. Added support for Perl's \C escape. This matches one byte, even in UTF8
711 mode. Unlike ".", it always matches newline, whatever the setting of
712 PCRE_DOTALL. However, PCRE does not permit \C to appear in lookbehind
713 assertions. Perl allows it, but it doesn't (in general) work because it can't
714 calculate the length of the lookbehind. At least, that's the case for Perl
715 5.8.0 - I've been told they are going to document that it doesn't work in
716 future.
718 18. Added an error diagnosis for escapes that PCRE does not support: these are
719 \L, \l, \N, \P, \p, \U, \u, and \X.
721 19. Although correctly diagnosing a missing ']' in a character class, PCRE was
722 reading past the end of the pattern in cases such as /[abcd/.
724 20. PCRE was getting more memory than necessary for patterns with classes that
725 contained both POSIX named classes and other characters, e.g. /[[:space:]abc/.
727 21. Added some code, conditional on #ifdef VPCOMPAT, to make life easier for
728 compiling PCRE for use with Virtual Pascal.
730 22. Small fix to the Makefile to make it work properly if the build is done
731 outside the source tree.
733 23. Added a new extension: a condition to go with recursion. If a conditional
734 subpattern starts with (?(R) the "true" branch is used if recursion has
735 happened, whereas the "false" branch is used only at the top level.
737 24. When there was a very long string of literal characters (over 255 bytes
738 without UTF support, over 250 bytes with UTF support), the computation of how
739 much memory was required could be incorrect, leading to segfaults or other
740 strange effects.
742 25. PCRE was incorrectly assuming anchoring (either to start of subject or to
743 start of line for a non-DOTALL pattern) when a pattern started with (.*) and
744 there was a subsequent back reference to those brackets. This meant that, for
745 example, /(.*)\d+\1/ failed to match "abc123bc". Unfortunately, it isn't
746 possible to check for precisely this case. All we can do is abandon the
747 optimization if .* occurs inside capturing brackets when there are any back
748 references whatsoever. (See below for a better fix that came later.)
750 26. The handling of the optimization for finding the first character of a
751 non-anchored pattern, and for finding a character that is required later in the
752 match were failing in some cases. This didn't break the matching; it just
753 failed to optimize when it could. The way this is done has been re-implemented.
755 27. Fixed typo in error message for invalid (?R item (it said "(?p").
757 28. Added a new feature that provides some of the functionality that Perl
758 provides with (?{...}). The facility is termed a "callout". The way it is done
759 in PCRE is for the caller to provide an optional function, by setting
760 pcre_callout to its entry point. Like pcre_malloc and pcre_free, this is a
761 global variable. By default it is unset, which disables all calling out. To get
762 the function called, the regex must include (?C) at appropriate points. This
763 is, in fact, equivalent to (?C0), and any number <= 255 may be given with (?C).
764 This provides a means of identifying different callout points. When PCRE
765 reaches such a point in the regex, if pcre_callout has been set, the external
766 function is called. It is provided with data in a structure called
767 pcre_callout_block, which is defined in pcre.h. If the function returns 0,
768 matching continues; if it returns a non-zero value, the match at the current
769 point fails. However, backtracking will occur if possible. [This was changed
770 later and other features added - see item 49 below.]
772 29. pcretest is upgraded to test the callout functionality. It provides a
773 callout function that displays information. By default, it shows the start of
774 the match and the current position in the text. There are some new data escapes
775 to vary what happens:
777 \C+ in addition, show current contents of captured substrings
778 \C- do not supply a callout function
779 \C!n return 1 when callout number n is reached
780 \C!n!m return 1 when callout number n is reached for the mth time
782 30. If pcregrep was called with the -l option and just a single file name, it
783 output "<stdin>" if a match was found, instead of the file name.
785 31. Improve the efficiency of the POSIX API to PCRE. If the number of capturing
786 slots is less than POSIX_MALLOC_THRESHOLD, use a block on the stack to pass to
787 pcre_exec(). This saves a malloc/free per call. The default value of
788 POSIX_MALLOC_THRESHOLD is 10; it can be changed by --with-posix-malloc-threshold
789 when configuring.
791 32. The default maximum size of a compiled pattern is 64K. There have been a
792 few cases of people hitting this limit. The code now uses macros to handle the
793 storing of links as offsets within the compiled pattern. It defaults to 2-byte
794 links, but this can be changed to 3 or 4 bytes by --with-link-size when
795 configuring. Tests 2 and 5 work only with 2-byte links because they output
796 debugging information about compiled patterns.
798 33. Internal code re-arrangements:
800 (a) Moved the debugging function for printing out a compiled regex into
801 its own source file (printint.c) and used #include to pull it into
802 pcretest.c and, when DEBUG is defined, into pcre.c, instead of having two
803 separate copies.
805 (b) Defined the list of op-code names for debugging as a macro in
806 internal.h so that it is next to the definition of the opcodes.
808 (c) Defined a table of op-code lengths for simpler skipping along compiled
809 code. This is again a macro in internal.h so that it is next to the
810 definition of the opcodes.
812 34. Added support for recursive calls to individual subpatterns, along the
813 lines of Robin Houston's patch (but implemented somewhat differently).
815 35. Further mods to the Makefile to help Win32. Also, added code to pcregrep to
816 allow it to read and process whole directories in Win32. This code was
817 contributed by Lionel Fourquaux; it has not been tested by me.
819 36. Added support for named subpatterns. The Python syntax (?P<name>...) is
820 used to name a group. Names consist of alphanumerics and underscores, and must
821 be unique. Back references use the syntax (?P=name) and recursive calls use
822 (?P>name) which is a PCRE extension to the Python extension. Groups still have
823 numbers. The function pcre_fullinfo() can be used after compilation to extract
824 a name/number map. There are three relevant calls:
826 PCRE_INFO_NAMEENTRYSIZE yields the size of each entry in the map
827 PCRE_INFO_NAMECOUNT yields the number of entries
828 PCRE_INFO_NAMETABLE yields a pointer to the map.
830 The map is a vector of fixed-size entries. The size of each entry depends on
831 the length of the longest name used. The first two bytes of each entry are the
832 group number, most significant byte first. There follows the corresponding
833 name, zero terminated. The names are in alphabetical order.
835 37. Make the maximum literal string in the compiled code 250 for the non-UTF-8
836 case instead of 255. Making it the same both with and without UTF-8 support
837 means that the same test output works with both.
839 38. There was a case of malloc(0) in the POSIX testing code in pcretest. Avoid
840 calling malloc() with a zero argument.
842 39. Change 25 above had to resort to a heavy-handed test for the .* anchoring
843 optimization. I've improved things by keeping a bitmap of backreferences with
844 numbers 1-31 so that if .* occurs inside capturing brackets that are not in
845 fact referenced, the optimization can be applied. It is unlikely that a
846 relevant occurrence of .* (i.e. one which might indicate anchoring or forcing
847 the match to follow \n) will appear inside brackets with a number greater than
848 31, but if it does, any back reference > 31 suppresses the optimization.
850 40. Added a new compile-time option PCRE_NO_AUTO_CAPTURE. This has the effect
851 of disabling numbered capturing parentheses. Any opening parenthesis that is
852 not followed by ? behaves as if it were followed by ?: but named parentheses
853 can still be used for capturing (and they will acquire numbers in the usual
854 way).
856 41. Redesigned the return codes from the match() function into yes/no/error so
857 that errors can be passed back from deep inside the nested calls. A malloc
858 failure while inside a recursive subpattern call now causes the
859 PCRE_ERROR_NOMEMORY return instead of quietly going wrong.
861 42. It is now possible to set a limit on the number of times the match()
862 function is called in a call to pcre_exec(). This facility makes it possible to
863 limit the amount of recursion and backtracking, though not in a directly
864 obvious way, because the match() function is used in a number of different
865 circumstances. The count starts from zero for each position in the subject
866 string (for non-anchored patterns). The default limit is, for compatibility, a
867 large number, namely 10 000 000. You can change this in two ways:
869 (a) When configuring PCRE before making, you can use --with-match-limit=n
870 to set a default value for the compiled library.
872 (b) For each call to pcre_exec(), you can pass a pcre_extra block in which
873 a different value is set. See 45 below.
875 If the limit is exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
877 43. Added a new function pcre_config(int, void *) to enable run-time extraction
878 of things that can be changed at compile time. The first argument specifies
879 what is wanted and the second points to where the information is to be placed.
880 The current list of available information is:
884 The output is an integer that is set to one if UTF-8 support is available;
885 otherwise it is set to zero.
889 The output is an integer that it set to the value of the code that is used for
890 newline. It is either LF (10) or CR (13).
894 The output is an integer that contains the number of bytes used for internal
895 linkage in compiled expressions. The value is 2, 3, or 4. See item 32 above.
899 The output is an integer that contains the threshold above which the POSIX
900 interface uses malloc() for output vectors. See item 31 above.
904 The output is an unsigned integer that contains the default limit of the number
905 of match() calls in a pcre_exec() execution. See 42 above.
907 44. pcretest has been upgraded by the addition of the -C option. This causes it
908 to extract all the available output from the new pcre_config() function, and to
909 output it. The program then exits immediately.
911 45. A need has arisen to pass over additional data with calls to pcre_exec() in
912 order to support additional features. One way would have been to define
913 pcre_exec2() (for example) with extra arguments, but this would not have been
914 extensible, and would also have required all calls to the original function to
915 be mapped to the new one. Instead, I have chosen to extend the mechanism that
916 is used for passing in "extra" data from pcre_study().
918 The pcre_extra structure is now exposed and defined in pcre.h. It currently
919 contains the following fields:
921 flags a bitmap indicating which of the following fields are set
922 study_data opaque data from pcre_study()
923 match_limit a way of specifying a limit on match() calls for a specific
924 call to pcre_exec()
925 callout_data data for callouts (see 49 below)
927 The flag bits are also defined in pcre.h, and are
933 The pcre_study() function now returns one of these new pcre_extra blocks, with
934 the actual study data pointed to by the study_data field, and the
935 PCRE_EXTRA_STUDY_DATA flag set. This can be passed directly to pcre_exec() as
936 before. That is, this change is entirely upwards-compatible and requires no
937 change to existing code.
939 If you want to pass in additional data to pcre_exec(), you can either place it
940 in a pcre_extra block provided by pcre_study(), or create your own pcre_extra
941 block.
943 46. pcretest has been extended to test the PCRE_EXTRA_MATCH_LIMIT feature. If a
944 data string contains the escape sequence \M, pcretest calls pcre_exec() several
945 times with different match limits, until it finds the minimum value needed for
946 pcre_exec() to complete. The value is then output. This can be instructive; for
947 most simple matches the number is quite small, but for pathological cases it
948 gets very large very quickly.
950 47. There's a new option for pcre_fullinfo() called PCRE_INFO_STUDYSIZE. It
951 returns the size of the data block pointed to by the study_data field in a
952 pcre_extra block, that is, the value that was passed as the argument to
953 pcre_malloc() when PCRE was getting memory in which to place the information
954 created by pcre_study(). The fourth argument should point to a size_t variable.
955 pcretest has been extended so that this information is shown after a successful
956 pcre_study() call when information about the compiled regex is being displayed.
958 48. Cosmetic change to Makefile: there's no need to have / after $(DESTDIR)
959 because what follows is always an absolute path. (Later: it turns out that this
960 is more than cosmetic for MinGW, because it doesn't like empty path
961 components.)
963 49. Some changes have been made to the callout feature (see 28 above):
965 (i) A callout function now has three choices for what it returns:
967 0 => success, carry on matching
968 > 0 => failure at this point, but backtrack if possible
969 < 0 => serious error, return this value from pcre_exec()
971 Negative values should normally be chosen from the set of PCRE_ERROR_xxx
972 values. In particular, returning PCRE_ERROR_NOMATCH forces a standard
973 "match failed" error. The error number PCRE_ERROR_CALLOUT is reserved for
974 use by callout functions. It will never be used by PCRE itself.
976 (ii) The pcre_extra structure (see 45 above) has a void * field called
977 callout_data, with corresponding flag bit PCRE_EXTRA_CALLOUT_DATA. The
978 pcre_callout_block structure has a field of the same name. The contents of
979 the field passed in the pcre_extra structure are passed to the callout
980 function in the corresponding field in the callout block. This makes it
981 easier to use the same callout-containing regex from multiple threads. For
982 testing, the pcretest program has a new data escape
984 \C*n pass the number n (may be negative) as callout_data
986 If the callout function in pcretest receives a non-zero value as
987 callout_data, it returns that value.
989 50. Makefile wasn't handling CFLAGS properly when compiling dftables. Also,
990 there were some redundant $(CFLAGS) in commands that are now specified as
991 $(LINK), which already includes $(CFLAGS).
993 51. Extensions to UTF-8 support are listed below. These all apply when (a) PCRE
994 has been compiled with UTF-8 support *and* pcre_compile() has been compiled
995 with the PCRE_UTF8 flag. Patterns that are compiled without that flag assume
996 one-byte characters throughout. Note that case-insensitive matching applies
997 only to characters whose values are less than 256. PCRE doesn't support the
998 notion of cases for higher-valued characters.
1000 (i) A character class whose characters are all within 0-255 is handled as
1001 a bit map, and the map is inverted for negative classes. Previously, a
1002 character > 255 always failed to match such a class; however it should
1003 match if the class was a negative one (e.g. [^ab]). This has been fixed.
1005 (ii) A negated character class with a single character < 255 is coded as
1006 "not this character" (OP_NOT). This wasn't working properly when the test
1007 character was multibyte, either singly or repeated.
1009 (iii) Repeats of multibyte characters are now handled correctly in UTF-8
1010 mode, for example: \x{100}{2,3}.
1012 (iv) The character escapes \b, \B, \d, \D, \s, \S, \w, and \W (either
1013 singly or repeated) now correctly test multibyte characters. However,
1014 PCRE doesn't recognize any characters with values greater than 255 as
1015 digits, spaces, or word characters. Such characters always match \D, \S,
1016 and \W, and never match \d, \s, or \w.
1018 (v) Classes may now contain characters and character ranges with values
1019 greater than 255. For example: [ab\x{100}-\x{400}].
1021 (vi) pcregrep now has a --utf-8 option (synonym -u) which makes it call
1022 PCRE in UTF-8 mode.
1024 52. The info request value PCRE_INFO_FIRSTCHAR has been renamed
1025 PCRE_INFO_FIRSTBYTE because it is a byte value. However, the old name is
1026 retained for backwards compatibility. (Note that LASTLITERAL is also a byte
1027 value.)
1029 53. The single man page has become too large. I have therefore split it up into
1030 a number of separate man pages. These also give rise to individual HTML pages;
1031 these are now put in a separate directory, and there is an index.html page that
1032 lists them all. Some hyperlinking between the pages has been installed.
1034 54. Added convenience functions for handling named capturing parentheses.
1036 55. Unknown escapes inside character classes (e.g. [\M]) and escapes that
1037 aren't interpreted therein (e.g. [\C]) are literals in Perl. This is now also
1038 true in PCRE, except when the PCRE_EXTENDED option is set, in which case they
1039 are faulted.
1041 56. Introduced HOST_CC and HOST_CFLAGS which can be set in the environment when
1042 calling configure. These values are used when compiling the dftables.c program
1043 which is run to generate the source of the default character tables. They
1044 default to the values of CC and CFLAGS. If you are cross-compiling PCRE,
1045 you will need to set these values.
1047 57. Updated the building process for Windows DLL, as provided by Fred Cox.
1050 Version 3.9 02-Jan-02
1051 ---------------------
1053 1. A bit of extraneous text had somehow crept into the pcregrep documentation.
1055 2. If --disable-static was given, the building process failed when trying to
1056 build pcretest and pcregrep. (For some reason it was using libtool to compile
1057 them, which is not right, as they aren't part of the library.)
1060 Version 3.8 18-Dec-01
1061 ---------------------
1063 1. The experimental UTF-8 code was completely screwed up. It was packing the
1064 bytes in the wrong order. How dumb can you get?
1067 Version 3.7 29-Oct-01
1068 ---------------------
1070 1. In updating pcretest to check change 1 of version 3.6, I screwed up.
1071 This caused pcretest, when used on the test data, to segfault. Unfortunately,
1072 this didn't happen under Solaris 8, where I normally test things.
1074 2. The Makefile had to be changed to make it work on BSD systems, where 'make'
1075 doesn't seem to recognize that ./xxx and xxx are the same file. (This entry
1076 isn't in ChangeLog distributed with 3.7 because I forgot when I hastily made
1077 this fix an hour or so after the initial 3.7 release.)
1080 Version 3.6 23-Oct-01
1081 ---------------------
1083 1. Crashed with /(sens|respons)e and \1ibility/ and "sense and sensibility" if
1084 offsets passed as NULL with zero offset count.
1086 2. The config.guess and config.sub files had not been updated when I moved to
1087 the latest autoconf.
1090 Version 3.5 15-Aug-01
1091 ---------------------
1093 1. Added some missing #if !defined NOPOSIX conditionals in pcretest.c that
1094 had been forgotten.
1096 2. By using declared but undefined structures, we can avoid using "void"
1097 definitions in pcre.h while keeping the internal definitions of the structures
1098 private.
1100 3. The distribution is now built using autoconf 2.50 and libtool 1.4. From a
1101 user point of view, this means that both static and shared libraries are built
1102 by default, but this can be individually controlled. More of the work of
1103 handling this static/shared cases is now inside libtool instead of PCRE's make
1104 file.
1106 4. The pcretest utility is now installed along with pcregrep because it is
1107 useful for users (to test regexs) and by doing this, it automatically gets
1108 relinked by libtool. The documentation has been turned into a man page, so
1109 there are now .1, .txt, and .html versions in /doc.
1111 5. Upgrades to pcregrep:
1112 (i) Added long-form option names like gnu grep.
1113 (ii) Added --help to list all options with an explanatory phrase.
1114 (iii) Added -r, --recursive to recurse into sub-directories.
1115 (iv) Added -f, --file to read patterns from a file.
1117 6. pcre_exec() was referring to its "code" argument before testing that
1118 argument for NULL (and giving an error if it was NULL).
1120 7. Upgraded Makefile.in to allow for compiling in a different directory from
1121 the source directory.
1123 8. Tiny buglet in pcretest: when pcre_fullinfo() was called to retrieve the
1124 options bits, the pointer it was passed was to an int instead of to an unsigned
1125 long int. This mattered only on 64-bit systems.
1127 9. Fixed typo (3.4/1) in pcre.h again. Sigh. I had changed pcre.h (which is
1128 generated) instead of pcre.in, which it its source. Also made the same change
1129 in several of the .c files.
1131 10. A new release of gcc defines printf() as a macro, which broke pcretest
1132 because it had an ifdef in the middle of a string argument for printf(). Fixed
1133 by using separate calls to printf().
1135 11. Added --enable-newline-is-cr and --enable-newline-is-lf to the configure
1136 script, to force use of CR or LF instead of \n in the source. On non-Unix
1137 systems, the value can be set in config.h.
1139 12. The limit of 200 on non-capturing parentheses is a _nesting_ limit, not an
1140 absolute limit. Changed the text of the error message to make this clear, and
1141 likewise updated the man page.
1143 13. The limit of 99 on the number of capturing subpatterns has been removed.
1144 The new limit is 65535, which I hope will not be a "real" limit.
1147 Version 3.4 22-Aug-00
1148 ---------------------
1150 1. Fixed typo in pcre.h: unsigned const char * changed to const unsigned char *.
1152 2. Diagnose condition (?(0) as an error instead of crashing on matching.
1155 Version 3.3 01-Aug-00
1156 ---------------------
1158 1. If an octal character was given, but the value was greater than \377, it
1159 was not getting masked to the least significant bits, as documented. This could
1160 lead to crashes in some systems.
1162 2. Perl 5.6 (if not earlier versions) accepts classes like [a-\d] and treats
1163 the hyphen as a literal. PCRE used to give an error; it now behaves like Perl.
1165 3. Added the functions pcre_free_substring() and pcre_free_substring_list().
1166 These just pass their arguments on to (pcre_free)(), but they are provided
1167 because some uses of PCRE bind it to non-C systems that can call its functions,
1168 but cannot call free() or pcre_free() directly.
1170 4. Add "make test" as a synonym for "make check". Corrected some comments in
1171 the Makefile.
1173 5. Add $(DESTDIR)/ in front of all the paths in the "install" target in the
1174 Makefile.
1176 6. Changed the name of pgrep to pcregrep, because Solaris has introduced a
1177 command called pgrep for grepping around the active processes.
1179 7. Added the beginnings of support for UTF-8 character strings.
1181 8. Arranged for the Makefile to pass over the settings of CC, CFLAGS, and
1182 RANLIB to ./ltconfig so that they are used by libtool. I think these are all
1183 the relevant ones. (AR is not passed because ./ltconfig does its own figuring
1184 out for the ar command.)
1187 Version 3.2 12-May-00
1188 ---------------------
1190 This is purely a bug fixing release.
1192 1. If the pattern /((Z)+|A)*/ was matched agained ZABCDEFG it matched Z instead
1193 of ZA. This was just one example of several cases that could provoke this bug,
1194 which was introduced by change 9 of version 2.00. The code for breaking
1195 infinite loops after an iteration that matches an empty string was't working
1196 correctly.
1198 2. The pcretest program was not imitating Perl correctly for the pattern /a*/g
1199 when matched against abbab (for example). After matching an empty string, it
1200 wasn't forcing anchoring when setting PCRE_NOTEMPTY for the next attempt; this
1201 caused it to match further down the string than it should.
1203 3. The code contained an inclusion of sys/types.h. It isn't clear why this
1204 was there because it doesn't seem to be needed, and it causes trouble on some
1205 systems, as it is not a Standard C header. It has been removed.
1207 4. Made 4 silly changes to the source to avoid stupid compiler warnings that
1208 were reported on the Macintosh. The changes were from
1210 while ((c = *(++ptr)) != 0 && c != '\n');
1211 to
1212 while ((c = *(++ptr)) != 0 && c != '\n') ;
1214 Totally extraordinary, but if that's what it takes...
1216 5. PCRE is being used in one environment where neither memmove() nor bcopy() is
1217 available. Added HAVE_BCOPY and an autoconf test for it; if neither
1218 HAVE_MEMMOVE nor HAVE_BCOPY is set, use a built-in emulation function which
1219 assumes the way PCRE uses memmove() (always moving upwards).
1221 6. PCRE is being used in one environment where strchr() is not available. There
1222 was only one use in pcre.c, and writing it out to avoid strchr() probably gives
1223 faster code anyway.
1226 Version 3.1 09-Feb-00
1227 ---------------------
1229 The only change in this release is the fixing of some bugs in Makefile.in for
1230 the "install" target:
1232 (1) It was failing to install pcreposix.h.
1234 (2) It was overwriting the pcre.3 man page with the pcreposix.3 man page.
1237 Version 3.0 01-Feb-00
1238 ---------------------
1240 1. Add support for the /+ modifier to perltest (to output $` like it does in
1241 pcretest).
1243 2. Add support for the /g modifier to perltest.
1245 3. Fix pcretest so that it behaves even more like Perl for /g when the pattern
1246 matches null strings.
1248 4. Fix perltest so that it doesn't do unwanted things when fed an empty
1249 pattern. Perl treats empty patterns specially - it reuses the most recent
1250 pattern, which is not what we want. Replace // by /(?#)/ in order to avoid this
1251 effect.
1253 5. The POSIX interface was broken in that it was just handing over the POSIX
1254 captured string vector to pcre_exec(), but (since release 2.00) PCRE has
1255 required a bigger vector, with some working space on the end. This means that
1256 the POSIX wrapper now has to get and free some memory, and copy the results.
1258 6. Added some simple autoconf support, placing the test data and the
1259 documentation in separate directories, re-organizing some of the
1260 information files, and making it build pcre-config (a GNU standard). Also added
1261 libtool support for building PCRE as a shared library, which is now the
1262 default.
1264 7. Got rid of the leading zero in the definition of PCRE_MINOR because 08 and
1265 09 are not valid octal constants. Single digits will be used for minor values
1266 less than 10.
1268 8. Defined REG_EXTENDED and REG_NOSUB as zero in the POSIX header, so that
1269 existing programs that set these in the POSIX interface can use PCRE without
1270 modification.
1272 9. Added a new function, pcre_fullinfo() with an extensible interface. It can
1273 return all that pcre_info() returns, plus additional data. The pcre_info()
1274 function is retained for compatibility, but is considered to be obsolete.
1276 10. Added experimental recursion feature (?R) to handle one common case that
1277 Perl 5.6 will be able to do with (?p{...}).
1279 11. Added support for POSIX character classes like [:alpha:], which Perl is
1280 adopting.
1283 Version 2.08 31-Aug-99
1284 ----------------------
1286 1. When startoffset was not zero and the pattern began with ".*", PCRE was not
1287 trying to match at the startoffset position, but instead was moving forward to
1288 the next newline as if a previous match had failed.
1290 2. pcretest was not making use of PCRE_NOTEMPTY when repeating for /g and /G,
1291 and could get into a loop if a null string was matched other than at the start
1292 of the subject.
1294 3. Added definitions of PCRE_MAJOR and PCRE_MINOR to pcre.h so the version can
1295 be distinguished at compile time, and for completeness also added PCRE_DATE.
1297 5. Added Paul Sokolovsky's minor changes to make it easy to compile a Win32 DLL
1298 in GnuWin32 environments.
1301 Version 2.07 29-Jul-99
1302 ----------------------
1304 1. The documentation is now supplied in plain text form and HTML as well as in
1305 the form of man page sources.
1307 2. C++ compilers don't like assigning (void *) values to other pointer types.
1308 In particular this affects malloc(). Although there is no problem in Standard
1309 C, I've put in casts to keep C++ compilers happy.
1311 3. Typo on pcretest.c; a cast of (unsigned char *) in the POSIX regexec() call
1312 should be (const char *).
1314 4. If NOPOSIX is defined, pcretest.c compiles without POSIX support. This may
1315 be useful for non-Unix systems who don't want to bother with the POSIX stuff.
1316 However, I haven't made this a standard facility. The documentation doesn't
1317 mention it, and the Makefile doesn't support it.
1319 5. The Makefile now contains an "install" target, with editable destinations at
1320 the top of the file. The pcretest program is not installed.
1322 6. pgrep -V now gives the PCRE version number and date.
1324 7. Fixed bug: a zero repetition after a literal string (e.g. /abcde{0}/) was
1325 causing the entire string to be ignored, instead of just the last character.
1327 8. If a pattern like /"([^\\"]+|\\.)*"/ is applied in the normal way to a
1328 non-matching string, it can take a very, very long time, even for strings of
1329 quite modest length, because of the nested recursion. PCRE now does better in
1330 some of these cases. It does this by remembering the last required literal
1331 character in the pattern, and pre-searching the subject to ensure it is present
1332 before running the real match. In other words, it applies a heuristic to detect
1333 some types of certain failure quickly, and in the above example, if presented
1334 with a string that has no trailing " it gives "no match" very quickly.
1336 9. A new runtime option PCRE_NOTEMPTY causes null string matches to be ignored;
1337 other alternatives are tried instead.
1340 Version 2.06 09-Jun-99
1341 ----------------------
1343 1. Change pcretest's output for amount of store used to show just the code
1344 space, because the remainder (the data block) varies in size between 32-bit and
1345 64-bit systems.
1347 2. Added an extra argument to pcre_exec() to supply an offset in the subject to
1348 start matching at. This allows lookbehinds to work when searching for multiple
1349 occurrences in a string.
1351 3. Added additional options to pcretest for testing multiple occurrences:
1353 /+ outputs the rest of the string that follows a match
1354 /g loops for multiple occurrences, using the new startoffset argument
1355 /G loops for multiple occurrences by passing an incremented pointer
1357 4. PCRE wasn't doing the "first character" optimization for patterns starting
1358 with \b or \B, though it was doing it for other lookbehind assertions. That is,
1359 it wasn't noticing that a match for a pattern such as /\bxyz/ has to start with
1360 the letter 'x'. On long subject strings, this gives a significant speed-up.
1363 Version 2.05 21-Apr-99
1364 ----------------------
1366 1. Changed the type of magic_number from int to long int so that it works
1367 properly on 16-bit systems.
1369 2. Fixed a bug which caused patterns starting with .* not to work correctly
1370 when the subject string contained newline characters. PCRE was assuming
1371 anchoring for such patterns in all cases, which is not correct because .* will
1372 not pass a newline unless PCRE_DOTALL is set. It now assumes anchoring only if
1373 DOTALL is set at top level; otherwise it knows that patterns starting with .*
1374 must be retried after every newline in the subject.
1377 Version 2.04 18-Feb-99
1378 ----------------------
1380 1. For parenthesized subpatterns with repeats whose minimum was zero, the
1381 computation of the store needed to hold the pattern was incorrect (too large).
1382 If such patterns were nested a few deep, this could multiply and become a real
1383 problem.
1385 2. Added /M option to pcretest to show the memory requirement of a specific
1386 pattern. Made -m a synonym of -s (which does this globally) for compatibility.
1388 3. Subpatterns of the form (regex){n,m} (i.e. limited maximum) were being
1389 compiled in such a way that the backtracking after subsequent failure was
1390 pessimal. Something like (a){0,3} was compiled as (a)?(a)?(a)? instead of
1391 ((a)((a)(a)?)?)? with disastrous performance if the maximum was of any size.
1394 Version 2.03 02-Feb-99
1395 ----------------------
1397 1. Fixed typo and small mistake in man page.
1399 2. Added 4th condition (GPL supersedes if conflict) and created separate
1400 LICENCE file containing the conditions.
1402 3. Updated pcretest so that patterns such as /abc\/def/ work like they do in
1403 Perl, that is the internal \ allows the delimiter to be included in the
1404 pattern. Locked out the use of \ as a delimiter. If \ immediately follows
1405 the final delimiter, add \ to the end of the pattern (to test the error).
1407 4. Added the convenience functions for extracting substrings after a successful
1408 match. Updated pcretest to make it able to test these functions.
1411 Version 2.02 14-Jan-99
1412 ----------------------
1414 1. Initialized the working variables associated with each extraction so that
1415 their saving and restoring doesn't refer to uninitialized store.
1417 2. Put dummy code into study.c in order to trick the optimizer of the IBM C
1418 compiler for OS/2 into generating correct code. Apparently IBM isn't going to
1419 fix the problem.
1421 3. Pcretest: the timing code wasn't using LOOPREPEAT for timing execution
1422 calls, and wasn't printing the correct value for compiling calls. Increased the
1423 default value of LOOPREPEAT, and the number of significant figures in the
1424 times.
1426 4. Changed "/bin/rm" in the Makefile to "-rm" so it works on Windows NT.
1428 5. Renamed "deftables" as "dftables" to get it down to 8 characters, to avoid
1429 a building problem on Windows NT with a FAT file system.
1432 Version 2.01 21-Oct-98
1433 ----------------------
1435 1. Changed the API for pcre_compile() to allow for the provision of a pointer
1436 to character tables built by pcre_maketables() in the current locale. If NULL
1437 is passed, the default tables are used.
1440 Version 2.00 24-Sep-98
1441 ----------------------
1443 1. Since the (>?) facility is in Perl 5.005, don't require PCRE_EXTRA to enable
1444 it any more.
1446 2. Allow quantification of (?>) groups, and make it work correctly.
1448 3. The first character computation wasn't working for (?>) groups.
1450 4. Correct the implementation of \Z (it is permitted to match on the \n at the
1451 end of the subject) and add 5.005's \z, which really does match only at the
1452 very end of the subject.
1454 5. Remove the \X "cut" facility; Perl doesn't have it, and (?> is neater.
1456 6. Remove the ability to specify CASELESS, MULTILINE, DOTALL, and
1457 DOLLAR_END_ONLY at runtime, to make it possible to implement the Perl 5.005
1458 localized options. All options to pcre_study() were also removed.
1460 7. Add other new features from 5.005:
1462 $(?<= positive lookbehind
1463 $(?<! negative lookbehind
1464 (?imsx-imsx) added the unsetting capability
1465 such a setting is global if at outer level; local otherwise
1466 (?imsx-imsx:) non-capturing groups with option setting
1467 (?(cond)re|re) conditional pattern matching
1469 A backreference to itself in a repeated group matches the previous
1470 captured string.
1472 8. General tidying up of studying (both automatic and via "study")
1473 consequential on the addition of new assertions.
1475 9. As in 5.005, unlimited repeated groups that could match an empty substring
1476 are no longer faulted at compile time. Instead, the loop is forcibly broken at
1477 runtime if any iteration does actually match an empty substring.
1479 10. Include the RunTest script in the distribution.
1481 11. Added tests from the Perl 5.005_02 distribution. This showed up a few
1482 discrepancies, some of which were old and were also with respect to 5.004. They
1483 have now been fixed.
1486 Version 1.09 28-Apr-98
1487 ----------------------
1489 1. A negated single character class followed by a quantifier with a minimum
1490 value of one (e.g. [^x]{1,6} ) was not compiled correctly. This could lead to
1491 program crashes, or just wrong answers. This did not apply to negated classes
1492 containing more than one character, or to minima other than one.
1495 Version 1.08 27-Mar-98
1496 ----------------------
1498 1. Add PCRE_UNGREEDY to invert the greediness of quantifiers.
1500 2. Add (?U) and (?X) to set PCRE_UNGREEDY and PCRE_EXTRA respectively. The
1501 latter must appear before anything that relies on it in the pattern.
1504 Version 1.07 16-Feb-98
1505 ----------------------
1507 1. A pattern such as /((a)*)*/ was not being diagnosed as in error (unlimited
1508 repeat of a potentially empty string).
1511 Version 1.06 23-Jan-98
1512 ----------------------
1514 1. Added Markus Oberhumer's little patches for C++.
1516 2. Literal strings longer than 255 characters were broken.
1519 Version 1.05 23-Dec-97
1520 ----------------------
1522 1. Negated character classes containing more than one character were failing if
1523 PCRE_CASELESS was set at run time.
1526 Version 1.04 19-Dec-97
1527 ----------------------
1529 1. Corrected the man page, where some "const" qualifiers had been omitted.
1531 2. Made debugging output print "{0,xxx}" instead of just "{,xxx}" to agree with
1532 input syntax.
1534 3. Fixed memory leak which occurred when a regex with back references was
1535 matched with an offsets vector that wasn't big enough. The temporary memory
1536 that is used in this case wasn't being freed if the match failed.
1538 4. Tidied pcretest to ensure it frees memory that it gets.
1540 5. Temporary memory was being obtained in the case where the passed offsets
1541 vector was exactly big enough.
1543 6. Corrected definition of offsetof() from change 5 below.
1545 7. I had screwed up change 6 below and broken the rules for the use of
1546 setjmp(). Now fixed.
1549 Version 1.03 18-Dec-97
1550 ----------------------
1552 1. A erroneous regex with a missing opening parenthesis was correctly
1553 diagnosed, but PCRE attempted to access brastack[-1], which could cause crashes
1554 on some systems.
1556 2. Replaced offsetof(real_pcre, code) by offsetof(real_pcre, code[0]) because
1557 it was reported that one broken compiler failed on the former because "code" is
1558 also an independent variable.
1560 3. The erroneous regex a[]b caused an array overrun reference.
1562 4. A regex ending with a one-character negative class (e.g. /[^k]$/) did not
1563 fail on data ending with that character. (It was going on too far, and checking
1564 the next character, typically a binary zero.) This was specific to the
1565 optimized code for single-character negative classes.
1567 5. Added a contributed patch from the TIN world which does the following:
1569 + Add an undef for memmove, in case the the system defines a macro for it.
1571 + Add a definition of offsetof(), in case there isn't one. (I don't know
1572 the reason behind this - offsetof() is part of the ANSI standard - but
1573 it does no harm).
1575 + Reduce the ifdef's in pcre.c using macro DPRINTF, thereby eliminating
1576 most of the places where whitespace preceded '#'. I have given up and
1577 allowed the remaining 2 cases to be at the margin.
1579 + Rename some variables in pcre to eliminate shadowing. This seems very
1580 pedantic, but does no harm, of course.
1582 6. Moved the call to setjmp() into its own function, to get rid of warnings
1583 from gcc -Wall, and avoided calling it at all unless PCRE_EXTRA is used.
1585 7. Constructs such as \d{8,} were compiling into the equivalent of
1586 \d{8}\d{0,65527} instead of \d{8}\d* which didn't make much difference to the
1587 outcome, but in this particular case used more store than had been allocated,
1588 which caused the bug to be discovered because it threw up an internal error.
1590 8. The debugging code in both pcre and pcretest for outputting the compiled
1591 form of a regex was going wrong in the case of back references followed by
1592 curly-bracketed repeats.
1595 Version 1.02 12-Dec-97
1596 ----------------------
1598 1. Typos in pcre.3 and comments in the source fixed.
1600 2. Applied a contributed patch to get rid of places where it used to remove
1601 'const' from variables, and fixed some signed/unsigned and uninitialized
1602 variable warnings.
1604 3. Added the "runtest" target to Makefile.
1606 4. Set default compiler flag to -O2 rather than just -O.
1609 Version 1.01 19-Nov-97
1610 ----------------------
1612 1. PCRE was failing to diagnose unlimited repeat of empty string for patterns
1613 like /([ab]*)*/, that is, for classes with more than one character in them.
1615 2. Likewise, it wasn't diagnosing patterns with "once-only" subpatterns, such
1616 as /((?>a*))*/ (a PCRE_EXTRA facility).
1619 Version 1.00 18-Nov-97
1620 ----------------------
1622 1. Added compile-time macros to support systems such as SunOS4 which don't have
1623 memmove() or strerror() but have other things that can be used instead.
1625 2. Arranged that "make clean" removes the executables.
1628 Version 0.99 27-Oct-97
1629 ----------------------
1631 1. Fixed bug in code for optimizing classes with only one character. It was
1632 initializing a 32-byte map regardless, which could cause it to run off the end
1633 of the memory it had got.
1635 2. Added, conditional on PCRE_EXTRA, the proposed (?>REGEX) construction.
1638 Version 0.98 22-Oct-97
1639 ----------------------
1641 1. Fixed bug in code for handling temporary memory usage when there are more
1642 back references than supplied space in the ovector. This could cause segfaults.
1645 Version 0.97 21-Oct-97
1646 ----------------------
1648 1. Added the \X "cut" facility, conditional on PCRE_EXTRA.
1650 2. Optimized negated single characters not to use a bit map.
1652 3. Brought error texts together as macro definitions; clarified some of them;
1653 fixed one that was wrong - it said "range out of order" when it meant "invalid
1654 escape sequence".
1656 4. Changed some char * arguments to const char *.
1658 5. Added PCRE_NOTBOL and PCRE_NOTEOL (from POSIX).
1660 6. Added the POSIX-style API wrapper in pcreposix.a and testing facilities in
1661 pcretest.
1664 Version 0.96 16-Oct-97
1665 ----------------------
1667 1. Added a simple "pgrep" utility to the distribution.
1669 2. Fixed an incompatibility with Perl: "{" is now treated as a normal character
1670 unless it appears in one of the precise forms "{ddd}", "{ddd,}", or "{ddd,ddd}"
1671 where "ddd" means "one or more decimal digits".
1673 3. Fixed serious bug. If a pattern had a back reference, but the call to
1674 pcre_exec() didn't supply a large enough ovector to record the related
1675 identifying subpattern, the match always failed. PCRE now remembers the number
1676 of the largest back reference, and gets some temporary memory in which to save
1677 the offsets during matching if necessary, in order to ensure that
1678 backreferences always work.
1680 4. Increased the compatibility with Perl in a number of ways:
1682 (a) . no longer matches \n by default; an option PCRE_DOTALL is provided
1683 to request this handling. The option can be set at compile or exec time.
1685 (b) $ matches before a terminating newline by default; an option
1686 PCRE_DOLLAR_ENDONLY is provided to override this (but not in multiline
1687 mode). The option can be set at compile or exec time.
1689 (c) The handling of \ followed by a digit other than 0 is now supposed to be
1690 the same as Perl's. If the decimal number it represents is less than 10
1691 or there aren't that many previous left capturing parentheses, an octal
1692 escape is read. Inside a character class, it's always an octal escape,
1693 even if it is a single digit.
1695 (d) An escaped but undefined alphabetic character is taken as a literal,
1696 unless PCRE_EXTRA is set. Currently this just reserves the remaining
1697 escapes.
1699 (e) {0} is now permitted. (The previous item is removed from the compiled
1700 pattern).
1702 5. Changed all the names of code files so that the basic parts are no longer
1703 than 10 characters, and abolished the teeny "globals.c" file.
1705 6. Changed the handling of character classes; they are now done with a 32-byte
1706 bit map always.
1708 7. Added the -d and /D options to pcretest to make it possible to look at the
1709 internals of compilation without having to recompile pcre.
1712 Version 0.95 23-Sep-97
1713 ----------------------
1715 1. Fixed bug in pre-pass concerning escaped "normal" characters such as \x5c or
1716 \x20 at the start of a run of normal characters. These were being treated as
1717 real characters, instead of the source characters being re-checked.
1720 Version 0.94 18-Sep-97
1721 ----------------------
1723 1. The functions are now thread-safe, with the caveat that the global variables
1724 containing pointers to malloc() and free() or alternative functions are the
1725 same for all threads.
1727 2. Get pcre_study() to generate a bitmap of initial characters for non-
1728 anchored patterns when this is possible, and use it if passed to pcre_exec().
1731 Version 0.93 15-Sep-97
1732 ----------------------
1734 1. /(b)|(:+)/ was computing an incorrect first character.
1736 2. Add pcre_study() to the API and the passing of pcre_extra to pcre_exec(),
1737 but not actually doing anything yet.
1739 3. Treat "-" characters in classes that cannot be part of ranges as literals,
1740 as Perl does (e.g. [-az] or [az-]).
1742 4. Set the anchored flag if a branch starts with .* or .*? because that tests
1743 all possible positions.
1745 5. Split up into different modules to avoid including unneeded functions in a
1746 compiled binary. However, compile and exec are still in one module. The "study"
1747 function is split off.
1749 6. The character tables are now in a separate module whose source is generated
1750 by an auxiliary program - but can then be edited by hand if required. There are
1751 now no calls to isalnum(), isspace(), isdigit(), isxdigit(), tolower() or
1752 toupper() in the code.
1754 7. Turn the malloc/free funtions variables into pcre_malloc and pcre_free and
1755 make them global. Abolish the function for setting them, as the caller can now
1756 set them directly.
1759 Version 0.92 11-Sep-97
1760 ----------------------
1762 1. A repeat with a fixed maximum and a minimum of 1 for an ordinary character
1763 (e.g. /a{1,3}/) was broken (I mis-optimized it).
1765 2. Caseless matching was not working in character classes if the characters in
1766 the pattern were in upper case.
1768 3. Make ranges like [W-c] work in the same way as Perl for caseless matching.
1770 4. Make PCRE_ANCHORED public and accept as a compile option.
1772 5. Add an options word to pcre_exec() and accept PCRE_ANCHORED and
1773 PCRE_CASELESS at run time. Add escapes \A and \I to pcretest to cause it to
1774 pass them.
1776 6. Give an error if bad option bits passed at compile or run time.
1778 7. Add PCRE_MULTILINE at compile and exec time, and (?m) as well. Add \M to
1779 pcretest to cause it to pass that flag.
1781 8. Add pcre_info(), to get the number of identifying subpatterns, the stored
1782 options, and the first character, if set.
1784 9. Recognize C+ or C{n,m} where n >= 1 as providing a fixed starting character.
1787 Version 0.91 10-Sep-97
1788 ----------------------
1790 1. PCRE was failing to diagnose unlimited repeats of subpatterns that could
1791 match the empty string as in /(a*)*/. It was looping and ultimately crashing.
1793 2. PCRE was looping on encountering an indefinitely repeated back reference to
1794 a subpattern that had matched an empty string, e.g. /(a|)\1*/. It now does what
1795 Perl does - treats the match as successful.
1797 ****

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