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code/trunk/maintain/README revision 97 by ph10, Mon Mar 5 12:36:47 2007 UTC code/trunk/maint/README revision 181 by ph10, Wed Jun 13 14:55:18 2007 UTC
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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. There are various file names in the scripts and  
4  programs; they assume that the pcre directory is current.  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  132html         A Perl script that converts a .1 or .3 man page into HTML.  part of the PCRE distribution tarballs. This document describes these files and
7    also contains some notes for maintainers. Its contents are:
8  Builducptable   A Perl script that creates the contents of the ucptable.h file  
9                  from two Unicode data files, which themselves are downloaded    Files in the maint directory
10                  from the Unicode web site.    Updating to a new Unicode release
11      Preparing for a PCRE release
12  CleanTxt        A Perl script that cleans up the output of "nroff -man" by    Making a PCRE release
13                  removing backspaces and other redundant text so as to produce    Long-term ideas (wish list)
14                  a readable .txt file.  
15    
16  Detrail         A Perl script that removes trailing spaces from files.  Files in the maint directory
17    ----------------------------
18  Index.html      A file that is copied as index.html into the doc/html  
19                  directory. It works like this so that doc/html can be deleted  Builducptable    A Perl script that creates the contents of the ucptable.h file
20                  and re-created from scratch.                   from two Unicode data files, which themselves are downloaded
21                     from the Unicode web site. Run this script in the "maint"
22  MakeRelease     My script for creating a new release. It processes the                   directory.
23                  documentation man pages into .text and HTML formats before  
24                  creating tarballs.  ManyConfigTests  A shell script that runs "configure, make, test" a number of
25                     times with different configuration settings.
26  Tech.Notes      Some notes about the internals of the PCRE code.  
27    Unicode.tables   The files in this directory, Scripts.txt and UnicodeData.txt,
28  Unicode.tables  The files in this directory, Scripts.txt and UnicodeData.txt,                   were downloaded from the Unicode web site. They contain
29                  were downloaded from the Unicode web site. They contain                   information about Unicode characters and scripts.
30                  information about Unicode characters and scripts.  
31    ucptest.c        A short C program for testing the Unicode property functions
32  ucptest.c       A short C program for testing the Unicode property functions in                   in pcre_ucp_searchfuncs.c, mainly useful after rebuilding the
33                  pcre_ucp_searchfuncs.c, mainly useful after rebuilding the                   Unicode property table. Compile and run this in the "maint"
34                  Unicode property table.                   directory.
35    
36  ucptestdata     A directory containing two files, testinput1 and testoutput1,  ucptestdata      A directory containing two files, testinput1 and testoutput1,
37                  to use in conjunction with the ucptest program.                   to use in conjunction with the ucptest program.
38    
39  utf8.c          A short C program for converting a Unicode code point into a  utf8.c           A short, freestanding C program for converting a Unicode code
40                  sequence of bytes in the UTF-8 encoding, and vice versa.                   point into a sequence of bytes in the UTF-8 encoding, and vice
41                     versa. If its argument is a hex number such as 0x1234, it
42  When there is a new release of Unicode, the files in Unicode.tables must be                   outputs a list of the equivalent UTF-8 bytes. If its argument
43  refreshed from the web site, and the Buildupctable script can then be run to                   is sequence of concatenated UTF-8 bytes (e.g. e188b4) it
44  generate a new version of ucptable.h. The ucptest program can be used to check                   treats them as a UTF-8 character and outputs the equivalent
45  that the resulting table works properly, using the data files in ucptestdata to                   code point in hex.
46  check a number of test characters.  
47    
48  ****  Updating to a new Unicode release
49    ---------------------------------
50    
51    When there is a new release of Unicode, the files in Unicode.tables must be
52    refreshed from the web site, and the Buildupctable script can then be run to
53    generate a new version of ucptable.h. The ucptest program can be used to check
54    that the resulting table works properly, using the data files in ucptestdata to
55    check a number of test characters.
56    
57    
58    Preparing for a PCRE release
59    ----------------------------
60    
61    This section contains a checklist of things that I consult before building a
62    distribution for a new release.
63    
64    . Ensure that the version number and version date are correct in configure.ac,
65      ChangeLog, and NEWS.
66    
67    . Run ./autogen.sh to ensure everything is up-to-date.
68    
69    . Compile and test with many different config options, and combinations of
70      options. The maint/ManyConfigTests script now encapsulates this testing.
71    
72    . Run perltest.pl on the test data for tests 1 and 4. The output should match
73      the PCRE test output, apart from the version identification at the top. The
74      other tests are not Perl-compatible (they use various special PCRE options).
75    
76    . Test with valgrind by running "RunTest valgrind". There is also "RunGrepTest
77      valgrind", though that takes quite a long time.
78    
79    . It may also useful to test with Electric Fence, though the fact that it
80      grumbles for missing free() calls can be a nuisance. (A missing free() in
81      pcretest is hardly a big problem.) To build with EF, use:
82    
83        LIBS='/usr/lib/libefence.a -lpthread' with ./configure.
84    
85      Then all normal runs use it to check for buffer overflow. Also run everything
86      with:
87    
88        EF_PROTECT_BELOW=1 <whatever>
89    
90      because there have been problems with lookbehinds that looked too far.
91    
92    . Test with the emulated memmove() function by undefining HAVE_MEMMOVE and
93      HAVE_BCOPY in config.h. You may see a number of "pcre_memmove defined but not
94      used" warnings for the modules in which there is no call to memmove(). These
95      can be ignored.
96    
97    . Documentation: check AUTHORS, COPYING, ChangeLog (check date), INSTALL,
98      LICENCE, NEWS (check date), NON-UNIX-USE, and README. Many of these won't
99      need changing, but over the long term things do change.
100    
101    . Man pages: Check all man pages for \ not followed by e or f or " because
102      that indicates a markup error.
103    
104    . When the release is built, test it on a number of different operating
105      systems if possible, and using different compilers as well. For example,
106      on Solaris it is helpful to test using Sun's cc compiler as a change from
107      gcc. Adding -xarch=v9 to the cc options does a 64-bit test, but it also
108      needs -S 64 for pcretest to increase the stack size for test 2.
109    
110    
111    Making a PCRE release
112    ---------------------
113    
114    Run PrepareRelease and commit the files that it changes (by removing trailing
115    spaces). Then run "make distcheck" to create the tarballs and the zipball.
116    
117    Don't forget to update Freshmeat when the new release is out, and to tell
118    webmaster@pcre.org and the mailing list.
119    
120    
121    Future ideas (wish list)
122    ------------------------
123    
124    This section records a list of ideas so that they do not get forgotten. They
125    vary enormously in their usefulness and potential for implementation. Some are
126    very sensible; some are rather wacky. Some have been on this list for years;
127    others are relatively new.
128    
129    . Optimization
130    
131      There are always ideas for new optimizations so as to speed up pattern
132      matching. Most of them try to save work by recognizing a non-match without
133      having to scan all the possibilities. These are some that I've recorded:
134    
135      * /((A{0,5}){0,5}){0,5}(something complex)/ on a non-matching string is very
136        slow, though Perl is fast. Can we speed up somehow? Convert to {0,125}?
137        OTOH, this is pathological - the user could easily fix it.
138    
139      * Turn ={4} into ==== ? (for speed). I once did an experiment, and it seems
140        to have little effect, and maybe makes things worse.
141    
142      * "Ends with literal string" - note that a single character doesn't gain much
143        over the existing "required byte" (reqbyte) feature that just saves one
144        byte.
145    
146      * These probably need to go in study():
147    
148        o Remember an initial string rather than just 1 char?
149    
150        o A required byte from alternatives - not just the last char, but an
151          earlier one if common to all alternatives.
152    
153        o Minimum length of subject needed.
154    
155        o Friedl contains other ideas.
156    
157    . If Perl gets to a consistent state over the settings of capturing sub-
158      patterns inside repeats, see if we can match it. One example of the
159      difference is the matching of /(main(O)?)+/ against mainOmain, where PCRE
160      leaves $2 set. In Perl, it's unset. Changing this in PCRE will be very hard
161      because I think it needs much more state to be remembered.
162    
163    . Perl 6 will be a revolution. Is it a revolution too far for PCRE?
164    
165    . Unicode
166    
167      * Note that in Perl, \s matches \pZ and similarly for \d, \w and the POSIX
168        character classes. For the moment, I've chosen not to support this for
169        backward compatibility, for speed, and because it would be messy to
170        implement.
171    
172      * A different approach to Unicode might be to use a typedef to do everything
173        in unsigned shorts instead of unsigned chars. Actually, we'd have to have a
174        new typedef to distinguish data from bits of compiled pattern that are in
175        bytes, I think. There would need to be conversion functions in and out. I
176        don't think this is particularly trivial - and anyway, Unicode now has
177        characters that need more than 16 bits, so is this at all sensible?
178    
179      * There has been a request for direct support of 16-bit characters and
180        UTF-16. However, since Unicode is moving beyond purely 16-bit characters,
181        is this worth it at all? One possible way of handling 16-bit characters
182        would be to "load" them in the same way that UTF-8 characters are loaded.
183    
184    . Allow errorptr and erroroffset to be NULL. I don't like this idea.
185    
186    . Line endings:
187    
188      * Option to use NUL as a line terminator in subject strings. This could now
189        be done relatively easily since the extension to support LF, CR, and CRLF.
190        If this is done, a suitable option for pcregrep is also required.
191    
192    . Option to provide the pattern with a length instead of with a NUL terminator.
193      This probably affects quite a few places in the code.
194    
195    . Catch SIGSEGV for stack overflows?
196    
197    . A feature to suspend a match via a callout was once requested.
198    
199    . Option to convert results into character offsets and character lengths.
200    
201    . Option for pcregrep to scan only the start of a file. I am not keen - this is
202      the job of "head".
203    
204    . A (non-Unix) user wanted pcregrep options to (a) list a file name just once,
205      preceded by a blank line, instead of adding it to every matched line, and (b)
206      support --outputfile=name.
207    
208    . Consider making UTF-8 and UCP the default for PCRE n.0 for some n > 7.
209    
210    . Add a user pointer to pcre_malloc/free functions -- some option would be
211      needed to retain backward compatibility.
212    
213    . Define a union for the results from pcre_fullinfo().
214    
215    . Provide a "random access to the subject" facility so that the way in which it
216      is stored is independent of PCRE. For efficiency, it probably isn't possible
217      to switch this dynamically. It would have to be specified when PCRE was
218      compiled. PCRE would then call a function every time it wanted a character.
219    
220    . There are new (*PRUNE) facilities in Perl 5.10, some of which it might be
221      relatively easy to implement.
222    
223    . Wild thought: the ability to compile from PCRE's internal byte code to a real
224      FSM and a very fast (third) matcher to process the result. There would be
225      even more restrictions than for pcre_dfa_exec(), however. This is not easy.
226    
227    . Should pcretest have some private locale data, to avoid relying on the
228      available locales for the test data, since different OS have different ideas?
229      This won't be as thorough a test, but perhaps that doesn't really matter.
230    
231    . pcregrep: add -rs for a sorted recurse? Having to store file names and sort
232      them will of course slow it down.
233    
234    . Someone suggested --disable-callout to save code space when callouts are
235      never wanted. This seems rather marginal.
236    
237    . "Cut" as described in Jeffrey Friedl's book, p364: \v and \V. The definitions
238      aren't yet clear enough for me. \v flushes saved states so that no
239      backtracking to anything earlier can happen; \V says "no more bumpalong", but
240      does it fail the current match? As described in the book, these aren't really
241      "cut" as in Prolog, are they? NOTE: (a) PCRE once had "cut", but it was
242      removed when atomic groups were introduced. (b) Perl 5.10 has some (*PRUNE)
243      features --
244    
245    . These are the Perl 5.10 backtracking control features (all of which are
246      described as "experimental" -- some of them "very experimental") that it
247      might be easy to add to PCRE. They all succeed when encountered, but act as
248      follows when backtracking:
249    
250      (*PRUNE)  fail this match attempt, but still bumpalong
251      (*SKIP)   fail this match attempt, bumpalong to current match point
252      (*THEN)   fail this branch, try next branch at same level or fail if none
253      (*COMMIT) fail this match attempt, suppress bumpalong
254      (*FAIL)   fail and backtrack (same as (?!) and that can be optimized)
255      (*F)      synonym for (*FAIL)
256      (*ACCEPT) behave as if end of pattern reached ("very experimental")
257    
258      Some of these can have arguments (*PRUNE:NAME) but I'm not sure whether they
259      make sense in the PCRE context.
260    
261    Philip Hazel
262    Email local part: ph10
263    Email domain: cam.ac.uk
264    Last updated: 13 June 2007

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