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+revision 181 by ph10,
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  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
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 Builducptable    A Perl script that crea
                   from two Unicode data files, which themselves are downloaded
                   from the Unicode web site. Run this script in the "maint"
                   directory.
  ManyConfigTests  A shell script that runs "configure, make, test" a number of
                   times with different configuration settings.
  Unicode.tables   The files in this directory, 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 functions
                   in pcre_ucp_searchfuncs.c, mainly useful after rebuilding the
                   Unicode property table. Compile and run this in the "maint"
                   directory.
  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
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 utf8.c           A short, freestanding C
                   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, and the Buildupctable script can then be run to
  generate a new version of ucptable.h. The ucptest program can be used to check
  that the resulting table works properly, using the data files in ucptestdata to
  check a number of test characters.
  Preparing for a PCRE release
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 distribution for a new release.
  . 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 and 4. The output should match
    the PCRE test output, apart from the version identification at the top. The
    other tests are not Perl-compatible (they use various special PCRE 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 date), INSTALL,
    LICENCE, NEWS (check 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.
  . 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
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 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 saves 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 Minimum length of subject needed.
      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 this 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 probably affects quite a few places in the code.
  . Catch SIGSEGV for stack overflows?
- . "Cut" as described in Jeffrey Friedl's book, p364: \v and \V. The definitions
-   aren't yet clear enough for me. \v flushes saved states so that no
-   backtracking to anything earlier can happen; \V says "no more bumpalong", but
-   does it fail the current match? As described in the book, these aren't really
-   "cut" as in Prolog, are they? NOTE: (a) PCRE once had "cut", but it was
-   removed when atomic groups were introduced. (b) Perl 5.10 has some (*PRUNE)
-   features -- see below.
  . 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 > 7.
  . 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.
  . There are new (*PRUNE) facilities in Perl 5.10, some of which it might be
    relatively easy to implement.
- . Also in Perl 5.10 are relative subroutine references (?&-1) and (?&+1) which
-   I didn't know about when I added some 5.10 features for PCRE 7.0. What about
-   (?(-1)... as a condition? That's an obvious extension, even if Perl 5.10
-   doesn't have it.
  . 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.
- . Re-arrange test 2: take out the link-size dependent stuff for a separate test
+ . Someone suggested --disable-callout to save code space when callouts are
-   that is run only when the link size *is* 2; leave in some non-numbered
+   never wanted. This seems rather marginal.
-   debugging tests using the new /Z feature.
+ . "Cut" as described in Jeffrey Friedl's book, p364: \v and \V. The definitions
- . Stan Switzer's goto replacement for longjmp, which is apparently very slow on
+   aren't yet clear enough for me. \v flushes saved states so that no
-   OS-X. This is used when stack recursion is disabled. It would be worth doing
+   backtracking to anything earlier can happen; \V says "no more bumpalong", but
-   some timing tests on other OS.
+   does it fail the current match? As described in the book, these aren't really
+   "cut" as in Prolog, are they? NOTE: (a) PCRE once had "cut", but it was
- . Someone suggested --disable-callout to save code space when callouts are
+   removed when atomic groups were introduced. (b) Perl 5.10 has some (*PRUNE)
-   never wanted. This seems rather marginal.
+   features --
- . Work needs doing so that the pcregrep tests work better with different
+ . These are the Perl 5.10 backtracking control features (all of which are
-   linebreak settings. Currently, some tests don't work when the input files
+   described as "experimental" -- some of them "very experimental") that it
-   do not have \n line endings.
+   might be easy to add to PCRE. They all succeed when encountered, but act as
+   follows when backtracking:
- . If the fr_FR locale isn't available for testing, try "french" instead,
-   because this may be available on Windows. It means modifying the test data,
+   (*PRUNE)  fail this match attempt, but still bumpalong
-   however.
+   (*SKIP)   fail this match attempt, bumpalong to current match point
+   (*THEN)   fail this branch, try next branch at same level or fail if none
+   (*COMMIT) fail this match attempt, suppress bumpalong
+   (*FAIL)   fail and backtrack (same as (?!) and that can be optimized)
+   (*F)      synonym for (*FAIL)
+   (*ACCEPT) behave as if end of pattern reached ("very experimental")
+   Some of these can have arguments (*PRUNE:NAME) but I'm not sure whether they
+   make sense in the PCRE context.
  Philip Hazel
  Email local part: ph10
  Email domain: cam.ac.uk
- Last updated: 24 April 2007
+ Last updated: 13 June 2007

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