Contents of /code/trunk/maint/README

MAINTENANCE README FOR PCRE
===========================

The files in the "maint" directory of the PCRE source contain data, scripts,
and programs that are used for the maintenance of PCRE, but which do not form
part of the PCRE distribution tarballs. This document describes these files and
also contains some notes for maintainers. Its contents are:

  Files in the maint directory
  Updating to a new Unicode release
  Preparing for a PCRE release
  Making a PCRE release
  Long-term ideas (wish list)


Files in the maint directory
============================

---------------- This file is now OBSOLETE and no longer used ----------------
Builducptable    A Perl script that creates the contents of the ucptable.h file
                 from two Unicode data files, which themselves are downloaded
                 from the Unicode web site. Run this script in the "maint"
                 directory.
---------------- This file is now OBSOLETE and no longer used ----------------

GenerateUtt.py   A Python script to generate part of the pcre_tables.c file
                 that contains Unicode script names in a long string with
                 offsets, which is tedious to maintain by hand.

ManyConfigTests  A shell script that runs "configure, make, test" a number of
                 times with different configuration settings.

MultiStage2.py   A Python script that generates the file pcre_ucd.c from three
                 Unicode data tables, which are themselves downloaded from the
                 Unicode web site. Run this script in the "maint" directory.
                 The generated file contains the tables for a 2-stage lookup
                 of Unicode properties.

pcre_chartables.c.non-standard
                 This is a set of character tables that came from a Windows
                 system. It has characters greater than 128 that are set as
                 spaces, amongst other things. I kept it so that it can be
                 used for testing from time to time.

README           This file.

Unicode.tables   The files in this directory (CaseFolding.txt, 
                 DerivedGeneralCategory.txt, GraphemeBreakProperty.txt,
                 Scripts.txt and UnicodeData.txt) were downloaded from the
                 Unicode web site. They contain information about Unicode
                 characters and scripts. 

ucptest.c        A short C program for testing the Unicode property macros
                 that do lookups in the pcre_ucd.c data, mainly useful after
                 rebuilding the Unicode property table. Compile and run this in
                 the "maint" directory (see comments at its head).

ucptestdata      A directory containing two files, testinput1 and testoutput1,
                 to use in conjunction with the ucptest program.

utf8.c           A short, freestanding C program for converting a Unicode code
                 point into a sequence of bytes in the UTF-8 encoding, and vice
                 versa. If its argument is a hex number such as 0x1234, it
                 outputs a list of the equivalent UTF-8 bytes. If its argument
                 is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
                 treats them as a UTF-8 character and outputs the equivalent
                 code point in hex.


Updating to a new Unicode release
=================================

When there is a new release of Unicode, the files in Unicode.tables must be
refreshed from the web site. If the new version of Unicode adds new character
scripts, the source file ucp.h and both the MultiStage2.py and the
GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
can be run to generate a new version of pcre_ucd.c, and GenerateUtt.py can be
run to generate the tricky tables for inclusion in pcre_tables.c.

If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
the cause is usually a missing (or misspelt) name in the list of scripts. I
couldn't find a straightforward list of scripts on the Unicode site, but
there's a useful Wikipedia page that list them, and notes the Unicode version
in which they were introduced:

http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts

The ucptest program can be compiled and used to check that the new tables in
pcre_ucd.c work properly, using the data files in ucptestdata to check a number
of test characters. The source file ucptest.c must be updated whenever new
Unicode script names are added.

Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
of Unicode script names.


Preparing for a PCRE release
============================

This section contains a checklist of things that I consult before building a
distribution for a new release.

. Ensure that the version number and version date are correct in configure.ac.

. Update the library version numbers in configure.ac according to the rules 
  given below.

. If new build options have been added, ensure that they are added to the CMake
  files as well as to the autoconf files. The relevant files are CMakeLists.txt
  and config-cmake.h.in. After making a release tarball, test it out with CMake 
  if there have been changes here.  

. Run ./autogen.sh to ensure everything is up-to-date.

. Compile and test with many different config options, and combinations of
  options. Also, test with valgrind by running "RunTest valgrind" and
  "RunGrepTest valgrind" (which takes quite a long time). The script
  maint/ManyConfigTests now encapsulates this testing. It runs tests with
  different configurations, and it also runs some of them with valgrind, all of
  which can take quite some time.

. Run perltest.pl on the test data for tests 1, 4, and 6. The output 
  should match the PCRE test output, apart from the version identification at
  the start of each test. The other tests are not Perl-compatible (they use
  various PCRE-specific features or options).

. It is possible to test with the emulated memmove() function by undefining
  HAVE_MEMMOVE and HAVE_BCOPY in config.h, though I do not do this often. You
  may see a number of "pcre_memmove defined but not used" warnings for the
  modules in which there is no call to memmove(). These can be ignored.

. Documentation: check AUTHORS, ChangeLog (check version and date), LICENCE, 
  NEWS (check version and date), NON-AUTOTOOLS-BUILD, and README. Many of these
  won't need changing, but over the long term things do change.

. I used to test new releases myself on a number of different operating
  systems, using different compilers as well. For example, on Solaris it is
  helpful to test using Sun's cc compiler as a change from gcc. Adding
  -xarch=v9 to the cc options does a 64-bit test, but it also needs -S 64 for
  pcretest to increase the stack size for test 2. Since I retired I can no
  longer do this, but instead I rely on putting out release candidates for
  folks on the pcre-dev list to test.
  

Updating version info for libtool
=================================

This set of rules for updating library version information came from a web page 
whose URL I have forgotten. The version information consists of three parts:
(current, revision, age).

1. Start with version information of 0:0:0 for each libtool library.

2. Update the version information only immediately before a public release of
   your software. More frequent updates are unnecessary, and only guarantee
   that the current interface number gets larger faster.

3. If the library source code has changed at all since the last update, then
   increment revision; c:r:a becomes c:r+1:a.

4. If any interfaces have been added, removed, or changed since the last
   update, increment current, and set revision to 0.

5. If any interfaces have been added since the last public release, then
   increment age.

6. If any interfaces have been removed or changed since the last public
   release, then set age to 0.

The following explanation may help in understanding the above rules a bit
better. Consider that there are three possible kinds of reaction from users to
changes in a shared library:

1. Programs using the previous version may use the new version as a drop-in
   replacement, and programs using the new version can also work with the
   previous one. In other words, no recompiling nor relinking is needed. In
   this case, increment revision only, don't touch current or age.

2. Programs using the previous version may use the new version as a drop-in
   replacement, but programs using the new version may use APIs not present in
   the previous one. In other words, a program linking against the new version
   may fail if linked against the old version at run time. In this case, set
   revision to 0, increment current and age.

3. Programs may need to be changed, recompiled, relinked in order to use the
   new version. Increment current, set revision and age to 0.


Making a PCRE release
=====================

Run PrepareRelease and commit the files that it changes (by removing trailing
spaces). The first thing this script does is to run CheckMan on the man pages;
if it finds any markup errors, it reports them and then aborts.

Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
and the zipball. Double-check with "svn status", then create an SVN tagged
copy:

  svn copy svn://vcs.exim.org/pcre/code/trunk \
           svn://vcs.exim.org/pcre/code/tags/pcre-8.xx

Don't forget to update Freshmeat when the new release is out, and to tell
webmaster@pcre.org and the mailing list. Also, update the list of version
numbers in Bugzilla (edit products).


Future ideas (wish list)
========================

This section records a list of ideas so that they do not get forgotten. They
vary enormously in their usefulness and potential for implementation. Some are
very sensible; some are rather wacky. Some have been on this list for years;
others are relatively new.

. Optimization

  There are always ideas for new optimizations so as to speed up pattern
  matching. Most of them try to save work by recognizing a non-match without
  having to scan all the possibilities. These are some that I've recorded:

  * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
    slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
    OTOH, this is pathological - the user could easily fix it.

  * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
    to have little effect, and maybe makes things worse.

  * "Ends with literal string" - note that a single character doesn't gain much
    over the existing "required byte" (reqbyte) feature that just remembers one
    data unit.

  * These probably need to go in pcre_study():

    o Remember an initial string rather than just 1 char?

    o A required data unit from alternatives - not just the last unit, but an
      earlier one if common to all alternatives.

    o Friedl contains other ideas.

  * pcre_study() does not set initial byte flags for Unicode property types
    such as \p; I don't know how much benefit there would be for, for example,
    setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
    \p{N}.

  * There is scope for more "auto-possessifying" in connection with \p and \P.

. If Perl gets to a consistent state over the settings of capturing sub-
  patterns inside repeats, see if we can match it. One example of the
  difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
  leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
  because I think it needs much more state to be remembered.

. Perl 6 will be a revolution. Is it a revolution too far for PCRE?

. Allow errorptr and erroroffset to be NULL. I don't like this idea.

. Line endings:

  * Option to use NUL as a line terminator in subject strings. This could now
    be done relatively easily since the extension to support LF, CR, and CRLF.
    If it is done, a suitable option for pcregrep is also required.

. Option to provide the pattern with a length instead of with a NUL terminator.
  This affects quite a few places in the code and is not trivial.

. Catch SIGSEGV for stack overflows?

. A feature to suspend a match via a callout was once requested.

. Option to convert results into character offsets and character lengths.

. Option for pcregrep to scan only the start of a file. I am not keen - this is
  the job of "head".

. A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
  preceded by a blank line, instead of adding it to every matched line, and (b)
  support --outputfile=name.

. Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
  (And now presumably UTF-16 and UCP for the 16-bit library, and UTF-32 and UCP
  for the 32-bit library.)

. Add a user pointer to pcre_malloc/free functions -- some option would be
  needed to retain backward compatibility.

. Define a union for the results from pcre_fullinfo().

. Provide a "random access to the subject" facility so that the way in which it
  is stored is independent of PCRE. For efficiency, it probably isn't possible
  to switch this dynamically. It would have to be specified when PCRE was
  compiled. PCRE would then call a function every time it wanted a character.

. Wild thought: the ability to compile from PCRE's internal byte code to a real
  FSM and a very fast (third) matcher to process the result. There would be
  even more restrictions than for pcre_dfa_exec(), however. This is not easy.
  This is probably obsolete now that we have the JIT support.

. Should pcretest have some private locale data, to avoid relying on the
  available locales for the test data, since different OS have different ideas?
  This won't be as thorough a test, but perhaps that doesn't really matter.

. pcregrep: add -rs for a sorted recurse? Having to store file names and sort
  them will of course slow it down.

. Someone suggested --disable-callout to save code space when callouts are
  never wanted. This seems rather marginal.

. Check names that consist entirely of digits: PCRE allows, but do Perl and
  Python, etc?

. A user suggested a parameter to limit the length of string matched, for
  example if the parameter is N, the current match should fail if the matched
  substring exceeds N. This could apply to both match functions. The value
  could be a new field in the extra block.

. Callouts with arguments: (?Cn:ARG) for instance.

. A user is going to supply a patch to generalize the API for user-specific
  memory allocation so that it is more flexible in threaded environments. This
  was promised a long time ago, and never appeared. However, this is a live 
  issue not only for threaded environments, but for libraries that use PCRE and 
  want not to be beholden to their caller's memory allocation. 

. Write a wrapper to maintain a structure with specified runtime parameters,
  such as recurse limit, and pass these to PCRE each time it is called. Also
  maybe malloc and free. A user sent a prototype. This relates the the previous 
  item. 

. Write a function that generates random matching strings for a compiled regex.

. Pcregrep: an option to specify the output line separator, either as a string
  or select from a fixed list. This is not dead easy, because at the moment it
  outputs whatever is in the input file.

. Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
  non-thread-safe patch showed that this can help performance for patterns
  where there are many alternatives. However, a simple thread-safe
  implementation that I tried made things worse in many simple cases, so this
  is not an obviously good thing.

. PCRE cannot at present distinguish between subpatterns with different names,
  but the same number (created by the use of ?|). In order to do so, a way of
  remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
  Now that (*MARK) has been implemented, it can perhaps be used as a way round
  this problem.

. Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
  "something" and the the #ifdef appears only in one place, in "something".

Philip Hazel
Email local part: ph10
Email domain: cam.ac.uk
Last updated: 09 November 2012
1	MAINTENANCE README FOR PCRE
2	===========================
3
4	The files in the "maint" directory of the PCRE source contain data, scripts,
5	and programs that are used for the maintenance of PCRE, but which do not form
6	part of the PCRE distribution tarballs. This document describes these files and
7	also contains some notes for maintainers. Its contents are:
8
9	Files in the maint directory
10	Updating to a new Unicode release
11	Preparing for a PCRE release
12	Making a PCRE release
13	Long-term ideas (wish list)
14
15
16	Files in the maint directory
17	============================
18
19	---------------- This file is now OBSOLETE and no longer used ----------------
20	Builducptable A Perl script that creates the contents of the ucptable.h file
21	from two Unicode data files, which themselves are downloaded
22	from the Unicode web site. Run this script in the "maint"
23	directory.
24	---------------- This file is now OBSOLETE and no longer used ----------------
25
26	GenerateUtt.py A Python script to generate part of the pcre_tables.c file
27	that contains Unicode script names in a long string with
28	offsets, which is tedious to maintain by hand.
29
30	ManyConfigTests A shell script that runs "configure, make, test" a number of
31	times with different configuration settings.
32
33	MultiStage2.py A Python script that generates the file pcre_ucd.c from three
34	Unicode data tables, which are themselves downloaded from the
35	Unicode web site. Run this script in the "maint" directory.
36	The generated file contains the tables for a 2-stage lookup
37	of Unicode properties.
38
39	pcre_chartables.c.non-standard
40	This is a set of character tables that came from a Windows
41	system. It has characters greater than 128 that are set as
42	spaces, amongst other things. I kept it so that it can be
43	used for testing from time to time.
44
45	README This file.
46
47	Unicode.tables The files in this directory (CaseFolding.txt,
48	DerivedGeneralCategory.txt, GraphemeBreakProperty.txt,
49	Scripts.txt and UnicodeData.txt) were downloaded from the
50	Unicode web site. They contain information about Unicode
51	characters and scripts.
52
53	ucptest.c A short C program for testing the Unicode property macros
54	that do lookups in the pcre_ucd.c data, mainly useful after
55	rebuilding the Unicode property table. Compile and run this in
56	the "maint" directory (see comments at its head).
57
58	ucptestdata A directory containing two files, testinput1 and testoutput1,
59	to use in conjunction with the ucptest program.
60
61	utf8.c A short, freestanding C program for converting a Unicode code
62	point into a sequence of bytes in the UTF-8 encoding, and vice
63	versa. If its argument is a hex number such as 0x1234, it
64	outputs a list of the equivalent UTF-8 bytes. If its argument
65	is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
66	treats them as a UTF-8 character and outputs the equivalent
67	code point in hex.
68
69
70	Updating to a new Unicode release
71	=================================
72
73	When there is a new release of Unicode, the files in Unicode.tables must be
74	refreshed from the web site. If the new version of Unicode adds new character
75	scripts, the source file ucp.h and both the MultiStage2.py and the
76	GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
77	can be run to generate a new version of pcre_ucd.c, and GenerateUtt.py can be
78	run to generate the tricky tables for inclusion in pcre_tables.c.
79
80	If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
81	the cause is usually a missing (or misspelt) name in the list of scripts. I
82	couldn't find a straightforward list of scripts on the Unicode site, but
83	there's a useful Wikipedia page that list them, and notes the Unicode version
84	in which they were introduced:
85
86	http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts
87
88	The ucptest program can be compiled and used to check that the new tables in
89	pcre_ucd.c work properly, using the data files in ucptestdata to check a number
90	of test characters. The source file ucptest.c must be updated whenever new
91	Unicode script names are added.
92
93	Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
94	of Unicode script names.
95
96
97	Preparing for a PCRE release
98	============================
99
100	This section contains a checklist of things that I consult before building a
101	distribution for a new release.
102
103	. Ensure that the version number and version date are correct in configure.ac.
104
105	. Update the library version numbers in configure.ac according to the rules
106	given below.
107
108	. If new build options have been added, ensure that they are added to the CMake
109	files as well as to the autoconf files. The relevant files are CMakeLists.txt
110	and config-cmake.h.in. After making a release tarball, test it out with CMake
111	if there have been changes here.
112
113	. Run ./autogen.sh to ensure everything is up-to-date.
114
115	. Compile and test with many different config options, and combinations of
116	options. Also, test with valgrind by running "RunTest valgrind" and
117	"RunGrepTest valgrind" (which takes quite a long time). The script
118	maint/ManyConfigTests now encapsulates this testing. It runs tests with
119	different configurations, and it also runs some of them with valgrind, all of
120	which can take quite some time.
121
122	. Run perltest.pl on the test data for tests 1, 4, and 6. The output
123	should match the PCRE test output, apart from the version identification at
124	the start of each test. The other tests are not Perl-compatible (they use
125	various PCRE-specific features or options).
126
127	. It is possible to test with the emulated memmove() function by undefining
128	HAVE_MEMMOVE and HAVE_BCOPY in config.h, though I do not do this often. You
129	may see a number of "pcre_memmove defined but not used" warnings for the
130	modules in which there is no call to memmove(). These can be ignored.
131
132	. Documentation: check AUTHORS, ChangeLog (check version and date), LICENCE,
133	NEWS (check version and date), NON-AUTOTOOLS-BUILD, and README. Many of these
134	won't need changing, but over the long term things do change.
135
136	. I used to test new releases myself on a number of different operating
137	systems, using different compilers as well. For example, on Solaris it is
138	helpful to test using Sun's cc compiler as a change from gcc. Adding
139	-xarch=v9 to the cc options does a 64-bit test, but it also needs -S 64 for
140	pcretest to increase the stack size for test 2. Since I retired I can no
141	longer do this, but instead I rely on putting out release candidates for
142	folks on the pcre-dev list to test.
143
144
145	Updating version info for libtool
146	=================================
147
148	This set of rules for updating library version information came from a web page
149	whose URL I have forgotten. The version information consists of three parts:
150	(current, revision, age).
151
152	1. Start with version information of 0:0:0 for each libtool library.
153
154	2. Update the version information only immediately before a public release of
155	your software. More frequent updates are unnecessary, and only guarantee
156	that the current interface number gets larger faster.
157
158	3. If the library source code has changed at all since the last update, then
159	increment revision; c:r:a becomes c:r+1:a.
160
161	4. If any interfaces have been added, removed, or changed since the last
162	update, increment current, and set revision to 0.
163
164	5. If any interfaces have been added since the last public release, then
165	increment age.
166
167	6. If any interfaces have been removed or changed since the last public
168	release, then set age to 0.
169
170	The following explanation may help in understanding the above rules a bit
171	better. Consider that there are three possible kinds of reaction from users to
172	changes in a shared library:
173
174	1. Programs using the previous version may use the new version as a drop-in
175	replacement, and programs using the new version can also work with the
176	previous one. In other words, no recompiling nor relinking is needed. In
177	this case, increment revision only, don't touch current or age.
178
179	2. Programs using the previous version may use the new version as a drop-in
180	replacement, but programs using the new version may use APIs not present in
181	the previous one. In other words, a program linking against the new version
182	may fail if linked against the old version at run time. In this case, set
183	revision to 0, increment current and age.
184
185	3. Programs may need to be changed, recompiled, relinked in order to use the
186	new version. Increment current, set revision and age to 0.
187
188
189	Making a PCRE release
190	=====================
191
192	Run PrepareRelease and commit the files that it changes (by removing trailing
193	spaces). The first thing this script does is to run CheckMan on the man pages;
194	if it finds any markup errors, it reports them and then aborts.
195
196	Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
197	and the zipball. Double-check with "svn status", then create an SVN tagged
198	copy:
199
200	svn copy svn://vcs.exim.org/pcre/code/trunk \
201	svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
202
203	Don't forget to update Freshmeat when the new release is out, and to tell
204	webmaster@pcre.org and the mailing list. Also, update the list of version
205	numbers in Bugzilla (edit products).
206
207
208	Future ideas (wish list)
209	========================
210
211	This section records a list of ideas so that they do not get forgotten. They
212	vary enormously in their usefulness and potential for implementation. Some are
213	very sensible; some are rather wacky. Some have been on this list for years;
214	others are relatively new.
215
216	. Optimization
217
218	There are always ideas for new optimizations so as to speed up pattern
219	matching. Most of them try to save work by recognizing a non-match without
220	having to scan all the possibilities. These are some that I've recorded:
221
222	* /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
223	slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
224	OTOH, this is pathological - the user could easily fix it.
225
226	* Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
227	to have little effect, and maybe makes things worse.
228
229	* "Ends with literal string" - note that a single character doesn't gain much
230	over the existing "required byte" (reqbyte) feature that just remembers one
231	data unit.
232
233	* These probably need to go in pcre_study():
234
235	o Remember an initial string rather than just 1 char?
236
237	o A required data unit from alternatives - not just the last unit, but an
238	earlier one if common to all alternatives.
239
240	o Friedl contains other ideas.
241
242	* pcre_study() does not set initial byte flags for Unicode property types
243	such as \p; I don't know how much benefit there would be for, for example,
244	setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
245	\p{N}.
246
247	* There is scope for more "auto-possessifying" in connection with \p and \P.
248
249	. If Perl gets to a consistent state over the settings of capturing sub-
250	patterns inside repeats, see if we can match it. One example of the
251	difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
252	leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
253	because I think it needs much more state to be remembered.
254
255	. Perl 6 will be a revolution. Is it a revolution too far for PCRE?
256
257	. Allow errorptr and erroroffset to be NULL. I don't like this idea.
258
259	. Line endings:
260
261	* Option to use NUL as a line terminator in subject strings. This could now
262	be done relatively easily since the extension to support LF, CR, and CRLF.
263	If it is done, a suitable option for pcregrep is also required.
264
265	. Option to provide the pattern with a length instead of with a NUL terminator.
266	This affects quite a few places in the code and is not trivial.
267
268	. Catch SIGSEGV for stack overflows?
269
270	. A feature to suspend a match via a callout was once requested.
271
272	. Option to convert results into character offsets and character lengths.
273
274	. Option for pcregrep to scan only the start of a file. I am not keen - this is
275	the job of "head".
276
277	. A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
278	preceded by a blank line, instead of adding it to every matched line, and (b)
279	support --outputfile=name.
280
281	. Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
282	(And now presumably UTF-16 and UCP for the 16-bit library, and UTF-32 and UCP
283	for the 32-bit library.)
284
285	. Add a user pointer to pcre_malloc/free functions -- some option would be
286	needed to retain backward compatibility.
287
288	. Define a union for the results from pcre_fullinfo().
289
290	. Provide a "random access to the subject" facility so that the way in which it
291	is stored is independent of PCRE. For efficiency, it probably isn't possible
292	to switch this dynamically. It would have to be specified when PCRE was
293	compiled. PCRE would then call a function every time it wanted a character.
294
295	. Wild thought: the ability to compile from PCRE's internal byte code to a real
296	FSM and a very fast (third) matcher to process the result. There would be
297	even more restrictions than for pcre_dfa_exec(), however. This is not easy.
298	This is probably obsolete now that we have the JIT support.
299
300	. Should pcretest have some private locale data, to avoid relying on the
301	available locales for the test data, since different OS have different ideas?
302	This won't be as thorough a test, but perhaps that doesn't really matter.
303
304	. pcregrep: add -rs for a sorted recurse? Having to store file names and sort
305	them will of course slow it down.
306
307	. Someone suggested --disable-callout to save code space when callouts are
308	never wanted. This seems rather marginal.
309
310	. Check names that consist entirely of digits: PCRE allows, but do Perl and
311	Python, etc?
312
313	. A user suggested a parameter to limit the length of string matched, for
314	example if the parameter is N, the current match should fail if the matched
315	substring exceeds N. This could apply to both match functions. The value
316	could be a new field in the extra block.
317
318	. Callouts with arguments: (?Cn:ARG) for instance.
319
320	. A user is going to supply a patch to generalize the API for user-specific
321	memory allocation so that it is more flexible in threaded environments. This
322	was promised a long time ago, and never appeared. However, this is a live
323	issue not only for threaded environments, but for libraries that use PCRE and
324	want not to be beholden to their caller's memory allocation.
325
326	. Write a wrapper to maintain a structure with specified runtime parameters,
327	such as recurse limit, and pass these to PCRE each time it is called. Also
328	maybe malloc and free. A user sent a prototype. This relates the the previous
329	item.
330
331	. Write a function that generates random matching strings for a compiled regex.
332
333	. Pcregrep: an option to specify the output line separator, either as a string
334	or select from a fixed list. This is not dead easy, because at the moment it
335	outputs whatever is in the input file.
336
337	. Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
338	non-thread-safe patch showed that this can help performance for patterns
339	where there are many alternatives. However, a simple thread-safe
340	implementation that I tried made things worse in many simple cases, so this
341	is not an obviously good thing.
342
343	. PCRE cannot at present distinguish between subpatterns with different names,
344	but the same number (created by the use of ?\|). In order to do so, a way of
345	remembering which subpattern numbered n matched is needed. Bugzilla #760.
346	Now that (*MARK) has been implemented, it can perhaps be used as a way round
347	this problem.
348
349	. Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
350	"something" and the the #ifdef appears only in one place, in "something".
351
352	Philip Hazel
353	Email local part: ph10
354	Email domain: cam.ac.uk
355	Last updated: 09 November 2012