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1  The files in the "maintain" directory of the PCRE source contain data, scripts,  MAINTENANCE README FOR PCRE
2  and programs that are used for the maintenance of PCRE, but do not form part of  ===========================
3  the PCRE distribution tarballs.  
4    The files in the "maint" directory of the PCRE source contain data, scripts,
5  Builducptable   A Perl script that creates the contents of the ucptable.h file  and programs that are used for the maintenance of PCRE, but which do not form
6                  from two Unicode data files, which themselves are downloaded  part of the PCRE distribution tarballs. This document describes these files and
7                  from the Unicode web site. Run this script in the "maintain"  also contains some notes for maintainers. Its contents are:
8                  directory.  
9      Files in the maint directory
10  Tech.Notes      Some notes about the internals of the PCRE code.    Updating to a new Unicode release
11      Preparing for a PCRE release
12  Unicode.tables  The files in this directory, Scripts.txt and UnicodeData.txt,    Making a PCRE release
13                  were downloaded from the Unicode web site. They contain    Long-term ideas (wish list)
14                  information about Unicode characters and scripts.  
15    
16  ucptest.c       A short C program for testing the Unicode property functions in  Files in the maint directory
17                  pcre_ucp_searchfuncs.c, mainly useful after rebuilding the  ============================
18                  Unicode property table. Compile and run this in the "maintain"  
19                  directory.  GenerateUtt.py   A Python script to generate part of the pcre_tables.c file
20                     that contains Unicode script names in a long string with
21  ucptestdata     A directory containing two files, testinput1 and testoutput1,                   offsets, which is tedious to maintain by hand.
22                  to use in conjunction with the ucptest program.  
23    ManyConfigTests  A shell script that runs "configure, make, test" a number of
24  utf8.c          A short, freestanding C program for converting a Unicode code                   times with different configuration settings.
25                  point into a sequence of bytes in the UTF-8 encoding, and vice  
26                  versa. If its argument is a hex number such as 0x1234, it  MultiStage2.py   A Python script that generates the file pcre_ucd.c from three
27                  outputs a list of the equivalent UTF-8 bytes. If its argument                   Unicode data tables, which are themselves downloaded from the
28                  is sequence of concatenated UTF-8 bytes (e.g. e188b4) it treats                   Unicode web site. Run this script in the "maint" directory.
29                  them as a UTF-8 character and outputs the equivalent code point                   The generated file contains the tables for a 2-stage lookup
30                  in hex.                   of Unicode properties.
31    
32  When there is a new release of Unicode, the files in Unicode.tables must be  pcre_chartables.c.non-standard
33  refreshed from the web site, and the Buildupctable script can then be run to                   This is a set of character tables that came from a Windows
34  generate a new version of ucptable.h. The ucptest program can be used to check                   system. It has characters greater than 128 that are set as
35  that the resulting table works properly, using the data files in ucptestdata to                   spaces, amongst other things. I kept it so that it can be
36  check a number of test characters.                   used for testing from time to time.
37    
38  ****  README           This file.
39    
40    Unicode.tables   The files in this directory (CaseFolding.txt,
41                     DerivedGeneralCategory.txt, GraphemeBreakProperty.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    
46    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                     the "maint" directory (see comments at its head).
50    
51    ucptestdata      A directory containing two files, testinput1 and testoutput1,
52                     to use in conjunction with the ucptest program.
53    
54    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    
62    
63    Updating to a new Unicode release
64    =================================
65    
66    When there is a new release of Unicode, the files in Unicode.tables must be
67    refreshed from the web site. If the new version of Unicode adds new character
68    scripts, the source file ucp.h and both the MultiStage2.py and the
69    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    
73    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    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    of test characters. The source file ucptest.c must be updated whenever new
84    Unicode script names are added.
85    
86    Note also that both the pcresyntax.3 and pcrepattern.3 man pages contain lists
87    of Unicode script names.
88    
89    
90    Preparing for a PCRE release
91    ============================
92    
93    This section contains a checklist of things that I consult before building a
94    distribution for a new release.
95    
96    . Ensure that the version number and version date are correct in configure.ac.
97    
98    . Update the library version numbers in configure.ac according to the rules
99      given below.
100    
101    . If new build options have been added, ensure that they are added to the CMake
102      files as well as to the autoconf files. The relevant files are CMakeLists.txt
103      and config-cmake.h.in. After making a release tarball, test it out with CMake
104      if there have been changes here.
105    
106    . Run ./autogen.sh to ensure everything is up-to-date.
107    
108    . Compile and test with many different config options, and combinations of
109      options. Also, test with valgrind by running "RunTest valgrind" and
110      "RunGrepTest valgrind" (which takes quite a long time). The script
111      maint/ManyConfigTests now encapsulates this testing. It runs tests with
112      different configurations, and it also runs some of them with valgrind, all of
113      which can take quite some time.
114    
115    . Run perltest.pl on the test data for tests 1, 4, and 6. The output
116      should match the PCRE test output, apart from the version identification at
117      the start of each test. The other tests are not Perl-compatible (they use
118      various PCRE-specific features or options).
119    
120    . It is possible to test with the emulated memmove() function by undefining
121      HAVE_MEMMOVE and HAVE_BCOPY in config.h, though I do not do this often. You
122      may see a number of "pcre_memmove defined but not used" warnings for the
123      modules in which there is no call to memmove(). These can be ignored.
124    
125    . Documentation: check AUTHORS, ChangeLog (check version and date), LICENCE,
126      NEWS (check version and date), NON-AUTOTOOLS-BUILD, and README. Many of these
127      won't need changing, but over the long term things do change.
128    
129    . I used to test new releases myself on a number of different operating
130      systems, using different compilers as well. For example, on Solaris it is
131      helpful to test using Sun's cc compiler as a change from gcc. Adding
132      -xarch=v9 to the cc options does a 64-bit test, but it also needs -S 64 for
133      pcretest to increase the stack size for test 2. Since I retired I can no
134      longer do this, but instead I rely on putting out release candidates for
135      folks on the pcre-dev list to test.
136    
137    
138    Updating version info for libtool
139    =================================
140    
141    This set of rules for updating library version information came from a web page
142    whose URL I have forgotten. The version information consists of three parts:
143    (current, revision, age).
144    
145    1. Start with version information of 0:0:0 for each libtool library.
146    
147    2. Update the version information only immediately before a public release of
148       your software. More frequent updates are unnecessary, and only guarantee
149       that the current interface number gets larger faster.
150    
151    3. If the library source code has changed at all since the last update, then
152       increment revision; c:r:a becomes c:r+1:a.
153    
154    4. If any interfaces have been added, removed, or changed since the last
155       update, increment current, and set revision to 0.
156    
157    5. If any interfaces have been added since the last public release, then
158       increment age.
159    
160    6. If any interfaces have been removed or changed since the last public
161       release, then set age to 0.
162    
163    The following explanation may help in understanding the above rules a bit
164    better. Consider that there are three possible kinds of reaction from users to
165    changes in a shared library:
166    
167    1. Programs using the previous version may use the new version as a drop-in
168       replacement, and programs using the new version can also work with the
169       previous one. In other words, no recompiling nor relinking is needed. In
170       this case, increment revision only, don't touch current or age.
171    
172    2. Programs using the previous version may use the new version as a drop-in
173       replacement, but programs using the new version may use APIs not present in
174       the previous one. In other words, a program linking against the new version
175       may fail if linked against the old version at run time. In this case, set
176       revision to 0, increment current and age.
177    
178    3. Programs may need to be changed, recompiled, relinked in order to use the
179       new version. Increment current, set revision and age to 0.
180    
181    
182    Making a PCRE release
183    =====================
184    
185    Run PrepareRelease and commit the files that it changes (by removing trailing
186    spaces). The first thing this script does is to run CheckMan on the man pages;
187    if it finds any markup errors, it reports them and then aborts.
188    
189    Once PrepareRelease has run clean, run "make distcheck" to create the tarballs
190    and the zipball. Double-check with "svn status", then create an SVN tagged
191    copy:
192    
193      svn copy svn://vcs.exim.org/pcre/code/trunk \
194               svn://vcs.exim.org/pcre/code/tags/pcre-8.xx
195    
196    Don't forget to update Freshmeat when the new release is out, and to tell
197    webmaster@pcre.org and the mailing list. Also, update the list of version
198    numbers in Bugzilla (edit products).
199    
200    
201    Future ideas (wish list)
202    ========================
203    
204    This section records a list of ideas so that they do not get forgotten. They
205    vary enormously in their usefulness and potential for implementation. Some are
206    very sensible; some are rather wacky. Some have been on this list for years;
207    others are relatively new.
208    
209    . Optimization
210    
211      There are always ideas for new optimizations so as to speed up pattern
212      matching. Most of them try to save work by recognizing a non-match without
213      having to scan all the possibilities. These are some that I've recorded:
214    
215      * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
216        slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
217        OTOH, this is pathological - the user could easily fix it.
218    
219      * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
220        to have little effect, and maybe makes things worse.
221    
222      * "Ends with literal string" - note that a single character doesn't gain much
223        over the existing "required byte" (reqbyte) feature that just remembers one
224        data unit.
225    
226      * These probably need to go in pcre_study():
227    
228        o Remember an initial string rather than just 1 char?
229    
230        o A required data unit from alternatives - not just the last unit, but an
231          earlier one if common to all alternatives.
232    
233        o Friedl contains other ideas.
234    
235      * pcre_study() does not set initial byte flags for Unicode property types
236        such as \p; I don't know how much benefit there would be for, for example,
237        setting the bits for 0-9 and all bytes >= xC0 when a pattern starts with
238        \p{N}.
239    
240      * There is scope for more "auto-possessifying" in connection with \p and \P.
241    
242    . If Perl gets to a consistent state over the settings of capturing sub-
243      patterns inside repeats, see if we can match it. One example of the
244      difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
245      leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
246      because I think it needs much more state to be remembered.
247    
248    . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
249    
250    . Allow errorptr and erroroffset to be NULL. I don't like this idea.
251    
252    . Line endings:
253    
254      * Option to use NUL as a line terminator in subject strings. This could now
255        be done relatively easily since the extension to support LF, CR, and CRLF.
256        If it is done, a suitable option for pcregrep is also required.
257    
258    . Option to provide the pattern with a length instead of with a NUL terminator.
259      This affects quite a few places in the code and is not trivial.
260    
261    . Catch SIGSEGV for stack overflows?
262    
263    . A feature to suspend a match via a callout was once requested.
264    
265    . Option to convert results into character offsets and character lengths.
266    
267    . Option for pcregrep to scan only the start of a file. I am not keen - this is
268      the job of "head".
269    
270    . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
271      preceded by a blank line, instead of adding it to every matched line, and (b)
272      support --outputfile=name.
273    
274    . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 8.
275      (And now presumably UTF-16 and UCP for the 16-bit library, and UTF-32 and UCP
276      for the 32-bit library.)
277    
278    . Add a user pointer to pcre_malloc/free functions -- some option would be
279      needed to retain backward compatibility.
280    
281    . Define a union for the results from pcre_fullinfo().
282    
283    . Provide a "random access to the subject" facility so that the way in which it
284      is stored is independent of PCRE. For efficiency, it probably isn't possible
285      to switch this dynamically. It would have to be specified when PCRE was
286      compiled. PCRE would then call a function every time it wanted a character.
287    
288    . Wild thought: the ability to compile from PCRE's internal byte code to a real
289      FSM and a very fast (third) matcher to process the result. There would be
290      even more restrictions than for pcre_dfa_exec(), however. This is not easy.
291      This is probably obsolete now that we have the JIT support.
292    
293    . Should pcretest have some private locale data, to avoid relying on the
294      available locales for the test data, since different OS have different ideas?
295      This won't be as thorough a test, but perhaps that doesn't really matter.
296    
297    . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
298      them will of course slow it down.
299    
300    . Someone suggested --disable-callout to save code space when callouts are
301      never wanted. This seems rather marginal.
302    
303    . Check names that consist entirely of digits: PCRE allows, but do Perl and
304      Python, etc?
305    
306    . A user suggested a parameter to limit the length of string matched, for
307      example if the parameter is N, the current match should fail if the matched
308      substring exceeds N. This could apply to both match functions. The value
309      could be a new field in the extra block.
310    
311    . Callouts with arguments: (?Cn:ARG) for instance.
312    
313    . A user is going to supply a patch to generalize the API for user-specific
314      memory allocation so that it is more flexible in threaded environments. This
315      was promised a long time ago, and never appeared. However, this is a live
316      issue not only for threaded environments, but for libraries that use PCRE and
317      want not to be beholden to their caller's memory allocation.
318    
319    . Write a wrapper to maintain a structure with specified runtime parameters,
320      such as recurse limit, and pass these to PCRE each time it is called. Also
321      maybe malloc and free. A user sent a prototype. This relates the the previous
322      item.
323    
324    . Write a function that generates random matching strings for a compiled regex.
325    
326    . Pcregrep: an option to specify the output line separator, either as a string
327      or select from a fixed list. This is not dead easy, because at the moment it
328      outputs whatever is in the input file.
329    
330    . Improve the code for duplicate checking in pcre_dfa_exec(). An incomplete,
331      non-thread-safe patch showed that this can help performance for patterns
332      where there are many alternatives. However, a simple thread-safe
333      implementation that I tried made things worse in many simple cases, so this
334      is not an obviously good thing.
335    
336    . PCRE cannot at present distinguish between subpatterns with different names,
337      but the same number (created by the use of ?|). In order to do so, a way of
338      remembering *which* subpattern numbered n matched is needed. Bugzilla #760.
339      Now that (*MARK) has been implemented, it can perhaps be used as a way round
340      this problem.
341    
342    . Instead of having #ifdef HAVE_CONFIG_H in each module, put #include
343      "something" and the the #ifdef appears only in one place, in "something".
344    
345    Philip Hazel
346    Email local part: ph10
347    Email domain: cam.ac.uk
348    Last updated: 07 December 2012

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