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.  

README           This file.

Unicode.tables   The files in this directory, DerivedGeneralCategory.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.
  
. If new build options have been added, ensure that they are added to the CMake
  files as well as to the autoconf files. 

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

. Compile and test with many different config options, and combinations of
  options. The maint/ManyConfigTests script now encapsulates this testing.

. Run perltest.pl on the test data for tests 1, 4, 6, and 11. The first two can 
  be run with Perl 5.8 or 5.10; the last two require Perl 5.10. 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).

. Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
  valgrind", though that takes quite a long time.

. It may also useful to test with Electric Fence, though the fact that it
  grumbles for missing free() calls can be a nuisance. (A missing free() in
  pcretest is hardly a big problem.) To build with EF, use:

    LIBS='/usr/lib/libefence.a -lpthread' with ./configure.

  Then all normal runs use it to check for buffer overflow. Also run everything
  with:

    EF_PROTECT_BELOW=1 <whatever>

  because there have been problems with lookbehinds that looked too far.

. Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
  HAVE_BCOPY in config.h. 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, COPYING, ChangeLog (check version and date), 
  INSTALL, LICENCE, NEWS (check version and date), NON-UNIX-USE, and README.
  Many of these won't need changing, but over the long term things do change.

. Man pages: Check all man pages for \ not followed by e or f or " because
  that indicates a markup error. However, there is one exception: pcredemo.3, 
  which is created from the pcredemo.c program. It contains three instances
  of \\n. 

. When the release is built, test it on a number of different operating
  systems if possible, and 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.


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

Run PrepareRelease and commit the files that it changes (by removing trailing
spaces). Then 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
    byte.

  * These probably need to go in study():

    o Remember an initial string rather than just 1 char?

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

    o Friedl contains other ideas.
    
. 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?

. Unicode

  * Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
    character classes. For the moment, I've chosen not to support this for
    backward compatibility, for speed, and because it would be messy to
    implement.

  * A different approach to Unicode might be to use a typedef to do everything
    in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
    new typedef to distinguish data from bits of compiled pattern that are in
    bytes, I think. There would need to be conversion functions in and out. I
    don't think this is particularly trivial - and anyway, Unicode now has
    characters that need more than 16 bits, so is this at all sensible?

  * There has been a request for direct support of 16-bit characters and
    UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
    is this worth it at all? One possible way of handling 16-bit characters
    would be to "load" them in the same way that UTF-8 characters are loaded.

. 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.

. 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.

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

. 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.
  
. 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.
  
. Make the longest lookbehind available via pcre_fullinfo(). This is not 
  straightforward because lookbehinds can be nested inside lookbehinds. This 
  case will have to be identified, and the amounts added. This should then give 
  the maximum possible lookbehind length. The reason for wanting this is to 
  help when implementing multi-segment matching using pcre_exec() with partial
  matching and overlapping segments.
  
. 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.
  
. Instead of having #ifdef HAVE_CONFIG_H in each module, put #include 
  "something" and the the #ifdef appears only in one place, in "something".
  
. Support for (*MARK) and arguments for (*PRUNE) and friends. 

Philip Hazel
Email local part: ph10
Email domain: cam.ac.uk
Last updated: 10 March 2010
1	ph10	122	MAINTENANCE README FOR PCRE
2	ph10	507	===========================
3	ph10	122
4	ph10	181	The files in the "maint" directory of the PCRE source contain data, scripts,
5	ph10	122	and programs that are used for the maintenance of PCRE, but which do not form
6	ph10	181	part of the PCRE distribution tarballs. This document describes these files and
7	ph10	122	also contains some notes for maintainers. Its contents are:
8	ph10	97
9	ph10	122	Files in the maint directory
10			Updating to a new Unicode release
11			Preparing for a PCRE release
12			Making a PCRE release
13	ph10	181	Long-term ideas (wish list)
14	ph10	122
15
16			Files in the maint directory
17	ph10	507	============================
18	ph10	122
19	ph10	507	---------------- This file is now OBSOLETE and no longer used ----------------
20	ph10	129	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	ph10	507	---------------- This file is now OBSOLETE and no longer used ----------------
25	ph10	181
26	ph10	351	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	ph10	129	ManyConfigTests A shell script that runs "configure, make, test" a number of
31			times with different configuration settings.
32	ph10	350
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	ph10	181
39	ph10	454	README This file.
40
41	ph10	350	Unicode.tables The files in this directory, DerivedGeneralCategory.txt,
42			Scripts.txt and UnicodeData.txt, were downloaded from the
43			Unicode web site. They contain information about Unicode
44			characters and scripts.
45	ph10	181
46	ph10	350	ucptest.c A short C program for testing the Unicode property macros
47			that do lookups in the pcre_ucd.c data, mainly useful after
48			rebuilding the Unicode property table. Compile and run this in
49	ph10	351	the "maint" directory (see comments at its head).
50	ph10	181
51	ph10	129	ucptestdata A directory containing two files, testinput1 and testoutput1,
52			to use in conjunction with the ucptest program.
53	ph10	181
54	ph10	129	utf8.c A short, freestanding C program for converting a Unicode code
55			point into a sequence of bytes in the UTF-8 encoding, and vice
56			versa. If its argument is a hex number such as 0x1234, it
57			outputs a list of the equivalent UTF-8 bytes. If its argument
58			is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
59			treats them as a UTF-8 character and outputs the equivalent
60			code point in hex.
61	ph10	97
62	ph10	181
63	ph10	122	Updating to a new Unicode release
64	ph10	507	=================================
65	ph10	122
66	ph10	181	When there is a new release of Unicode, the files in Unicode.tables must be
67	ph10	454	refreshed from the web site. If the new version of Unicode adds new character
68	ph10	352	scripts, the source file ucp.h and both the MultiStage2.py and the
69	ph10	454	GenerateUtt.py scripts must be edited to add the new names. Then MultiStage2.py
70			can be run to generate a new version of pcre_ucd.c, and GenerateUtt.py can be
71			run to generate the tricky tables for inclusion in pcre_tables.c.
72	ph10	122
73	ph10	491	If MultiStage2.py gives the error "ValueError: list.index(x): x not in list",
74			the cause is usually a missing (or misspelt) name in the list of scripts. I
75			couldn't find a straightforward list of scripts on the Unicode site, but
76			there's a useful Wikipedia page that list them, and notes the Unicode version
77			in which they were introduced:
78
79			http://en.wikipedia.org/wiki/Unicode_scripts#Table_of_Unicode_scripts
80
81	ph10	454	The ucptest program can be compiled and used to check that the new tables in
82			pcre_ucd.c work properly, using the data files in ucptestdata to check a number
83	ph10	491	of test characters. The source file ucptest.c must be updated whenever new
84			Unicode script names are added.
85	ph10	122
86	ph10	491	Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
87			of Unicode script names.
88	ph10	351
89	ph10	491
90	ph10	122	Preparing for a PCRE release
91	ph10	507	============================
92	ph10	122
93			This section contains a checklist of things that I consult before building a
94			distribution for a new release.
95
96	ph10	454	. Ensure that the version number and version date are correct in configure.ac.
97	ph10	292
98			. If new build options have been added, ensure that they are added to the CMake
99			files as well as to the autoconf files.
100	ph10	122
101			. Run ./autogen.sh to ensure everything is up-to-date.
102
103	ph10	181	. Compile and test with many different config options, and combinations of
104	ph10	129	options. The maint/ManyConfigTests script now encapsulates this testing.
105	ph10	181
106	ph10	454	. Run perltest.pl on the test data for tests 1, 4, 6, and 11. The first two can
107			be run with Perl 5.8 or 5.10; the last two require Perl 5.10. The output
108			should match the PCRE test output, apart from the version identification at
109			the start of each test. The other tests are not Perl-compatible (they use
110			various PCRE-specific features or options).
111	ph10	122
112			. Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
113			valgrind", though that takes quite a long time.
114	ph10	181
115			. It may also useful to test with Electric Fence, though the fact that it
116			grumbles for missing free() calls can be a nuisance. (A missing free() in
117	ph10	122	pcretest is hardly a big problem.) To build with EF, use:
118	ph10	181
119	ph10	122	LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
120
121			Then all normal runs use it to check for buffer overflow. Also run everything
122			with:
123	ph10	181
124			EF_PROTECT_BELOW=1 <whatever>
125
126			because there have been problems with lookbehinds that looked too far.
127
128			. Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
129			HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
130	ph10	155	used" warnings for the modules in which there is no call to memmove(). These
131			can be ignored.
132	ph10	122
133	ph10	454	. Documentation: check AUTHORS, COPYING, ChangeLog (check version and date),
134			INSTALL, LICENCE, NEWS (check version and date), NON-UNIX-USE, and README.
135			Many of these won't need changing, but over the long term things do change.
136	ph10	181
137	ph10	122	. Man pages: Check all man pages for \ not followed by e or f or " because
138	ph10	507	that indicates a markup error. However, there is one exception: pcredemo.3,
139			which is created from the pcredemo.c program. It contains three instances
140			of \\n.
141	ph10	122
142	ph10	181	. When the release is built, test it on a number of different operating
143	ph10	155	systems if possible, and using different compilers as well. For example,
144			on Solaris it is helpful to test using Sun's cc compiler as a change from
145			gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
146			needs -S 64 for pcretest to increase the stack size for test 2.
147	ph10	122
148	ph10	155
149	ph10	122	Making a PCRE release
150	ph10	507	=====================
151	ph10	122
152			Run PrepareRelease and commit the files that it changes (by removing trailing
153	ph10	155	spaces). Then run "make distcheck" to create the tarballs and the zipball.
154	ph10	212	Double-check with "svn status", then create an SVN tagged copy:
155	ph10	122
156	ph10	212	svn copy svn://vcs.exim.org/pcre/code/trunk \
157	ph10	454	svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
158	ph10	212
159	ph10	122	Don't forget to update Freshmeat when the new release is out, and to tell
160	ph10	507	webmaster@pcre.org and the mailing list. Also, update the list of version
161			numbers in Bugzilla (edit products).
162	ph10	122
163
164			Future ideas (wish list)
165	ph10	507	========================
166	ph10	122
167			This section records a list of ideas so that they do not get forgotten. They
168	ph10	181	vary enormously in their usefulness and potential for implementation. Some are
169	ph10	122	very sensible; some are rather wacky. Some have been on this list for years;
170			others are relatively new.
171
172			. Optimization
173
174	ph10	181	There are always ideas for new optimizations so as to speed up pattern
175			matching. Most of them try to save work by recognizing a non-match without
176	ph10	122	having to scan all the possibilities. These are some that I've recorded:
177
178			* /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
179			slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
180	ph10	181	OTOH, this is pathological - the user could easily fix it.
181
182	ph10	122	* Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
183			to have little effect, and maybe makes things worse.
184	ph10	181
185			* "Ends with literal string" - note that a single character doesn't gain much
186	ph10	454	over the existing "required byte" (reqbyte) feature that just remembers one
187	ph10	122	byte.
188	ph10	181
189	ph10	122	* These probably need to go in study():
190	ph10	181
191	ph10	122	o Remember an initial string rather than just 1 char?
192	ph10	181
193	ph10	122	o A required byte from alternatives - not just the last char, but an
194			earlier one if common to all alternatives.
195	ph10	181
196	ph10	122	o Friedl contains other ideas.
197	ph10	454
198	ph10	122	. If Perl gets to a consistent state over the settings of capturing sub-
199			patterns inside repeats, see if we can match it. One example of the
200			difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
201			leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
202			because I think it needs much more state to be remembered.
203
204	ph10	181	. Perl 6 will be a revolution. Is it a revolution too far for PCRE?
205
206	ph10	122	. Unicode
207
208	ph10	181	* Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
209			character classes. For the moment, I've chosen not to support this for
210			backward compatibility, for speed, and because it would be messy to
211	ph10	122	implement.
212	ph10	181
213	ph10	122	* A different approach to Unicode might be to use a typedef to do everything
214			in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
215			new typedef to distinguish data from bits of compiled pattern that are in
216			bytes, I think. There would need to be conversion functions in and out. I
217			don't think this is particularly trivial - and anyway, Unicode now has
218			characters that need more than 16 bits, so is this at all sensible?
219	ph10	181
220	ph10	122	* There has been a request for direct support of 16-bit characters and
221			UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
222			is this worth it at all? One possible way of handling 16-bit characters
223			would be to "load" them in the same way that UTF-8 characters are loaded.
224	ph10	181
225	ph10	122	. Allow errorptr and erroroffset to be NULL. I don't like this idea.
226
227			. Line endings:
228
229			* Option to use NUL as a line terminator in subject strings. This could now
230			be done relatively easily since the extension to support LF, CR, and CRLF.
231	ph10	454	If it is done, a suitable option for pcregrep is also required.
232	ph10	181
233	ph10	122	. Option to provide the pattern with a length instead of with a NUL terminator.
234	ph10	454	This affects quite a few places in the code and is not trivial.
235	ph10	122
236	ph10	181	. Catch SIGSEGV for stack overflows?
237	ph10	122
238			. A feature to suspend a match via a callout was once requested.
239
240			. Option to convert results into character offsets and character lengths.
241
242	ph10	181	. Option for pcregrep to scan only the start of a file. I am not keen - this is
243	ph10	122	the job of "head".
244	ph10	181
245			. A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
246	ph10	122	preceded by a blank line, instead of adding it to every matched line, and (b)
247			support --outputfile=name.
248	ph10	181
249	ph10	454	. Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
250	ph10	122
251	ph10	181	. Add a user pointer to pcre_malloc/free functions -- some option would be
252	ph10	122	needed to retain backward compatibility.
253	ph10	181
254	ph10	122	. Define a union for the results from pcre_fullinfo().
255
256	ph10	181	. Provide a "random access to the subject" facility so that the way in which it
257			is stored is independent of PCRE. For efficiency, it probably isn't possible
258	ph10	122	to switch this dynamically. It would have to be specified when PCRE was
259			compiled. PCRE would then call a function every time it wanted a character.
260	ph10	181
261	ph10	122	. Wild thought: the ability to compile from PCRE's internal byte code to a real
262			FSM and a very fast (third) matcher to process the result. There would be
263			even more restrictions than for pcre_dfa_exec(), however. This is not easy.
264	ph10	181
265	ph10	122	. Should pcretest have some private locale data, to avoid relying on the
266			available locales for the test data, since different OS have different ideas?
267			This won't be as thorough a test, but perhaps that doesn't really matter.
268	ph10	181
269			. pcregrep: add -rs for a sorted recurse? Having to store file names and sort
270	ph10	122	them will of course slow it down.
271
272	ph10	181	. Someone suggested --disable-callout to save code space when callouts are
273			never wanted. This seems rather marginal.
274	ph10	212
275			. Check names that consist entirely of digits: PCRE allows, but do Perl and
276			Python, etc?
277	ph10	372
278			. A user suggested a parameter to limit the length of string matched, for
279			example if the parameter is N, the current match should fail if the matched
280			substring exceeds N. This could apply to both match functions. The value
281			could be a new field in the extra block.
282
283			. Callouts with arguments: (?Cn:ARG) for instance.
284	ph10	122
285	ph10	372	. A user is going to supply a patch to generalize the API for user-specific
286	ph10	507	memory allocation so that it is more flexible in threaded environments. This
287	ph10	454	was promised a long time ago, and never appeared...
288
289			. Write a function that generates random matching strings for a compiled regex.
290	ph10	372
291	ph10	454	. Write a wrapper to maintain a structure with specified runtime parameters,
292			such as recurse limit, and pass these to PCRE each time it is called. Also
293			maybe malloc and free. A user sent a prototype.
294
295			. Pcregrep: an option to specify the output line separator, either as a string
296			or select from a fixed list. This is not dead easy, because at the moment it
297			outputs whatever is in the input file.
298
299			. Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
300			non-thread-safe patch showed that this can help performance for patterns
301			where there are many alternatives. However, a simple thread-safe
302			implementation that I tried made things worse in many simple cases, so this
303			is not an obviously good thing.
304
305			. Make the longest lookbehind available via pcre_fullinfo(). This is not
306			straightforward because lookbehinds can be nested inside lookbehinds. This
307			case will have to be identified, and the amounts added. This should then give
308			the maximum possible lookbehind length. The reason for wanting this is to
309			help when implementing multi-segment matching using pcre_exec() with partial
310			matching and overlapping segments.
311
312			. PCRE cannot at present distinguish between subpatterns with different names,
313			but the same number (created by the use of ?\|). In order to do so, a way of
314			remembering which subpattern numbered n matched is needed. Bugzilla #760.
315	ph10	507
316			. Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
317			"something" and the the #ifdef appears only in one place, in "something".
318
319			. Support for (MARK) and arguments for (PRUNE) and friends.
320	ph10	454
321	ph10	122	Philip Hazel
322			Email local part: ph10
323			Email domain: cam.ac.uk
324	ph10	507	Last updated: 10 March 2010