#+TITLE: README for Recode #+OPTIONS: H:2 toc:2

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** What is Recode? Here is version 3.6 for the Recode program and library. Hereafter, Recode means the whole package, recode means the executable program. Glance through this =README= file before starting configuration. Make sure you read files =ABOUT-NLS= and =INSTALL= if you are not familiar with them already.

The Recode library converts files between character sets and usages. It recognises or produces over 200 different character sets (or about 300 if combined with an iconv library) and transliterates files between almost any pair. When exact transliteration are not possible, it gets rid of offending characters or falls back on approximations. The recode program is a handy front-end to the library.

The Recode program and library have been written by François Pinard, yet it significantly reuses tabular works from Keld Simonsen. It is an evolving package, and specifications might change in future releases.

On various Unix systems, Recode is usually compiled from sources, see the [[Installation]] section below. On Linux, it often comes bundled. Recode had been ported to other popular systems. See both [[http:/contrib.html][contrib/README]] and the [[Non-Unix ports]] section below, to find some more information about these.

** Reports and collaboration Send bug reports to [[mailto:recode-bugs@iro.umontreal.ca][this address]], or if you are comfortable with GitHub facilities, through [[https://github.com/pinard/Recode/issues][GitHub Issues]]. A bug report is an adequate description of the problem: your input, what you expected, what you got, and why this is wrong. Diffs are welcome, but they only describe a solution, from which the problem might be uneasy to infer. If needed, submit actual data files with your report. Small data files are preferred. Big files may sometimes be necessary, but do not send them on the mailing list; rather take special arrangement with the maintainer.

Your feedback will help us to make a better and more portable package. Consider documentation errors as bugs, and report them as such. If you develop anything pertaining to Recode or have suggestions, let us know and share your findings by writing at [[mailto:recode-forum@iro.umontreal.ca][Recode forum]]. You may also choose to directly write to [[mailto:pinard@iro.umontreal.ca][the author]], yet be warned that such correspondence is often visible for a while through the Recode Web site.

If you feel like receiving releases and pretest announcements for the Recode package, send a message to [[mailto:majordomo@iro.umontreal.ca][this Majordomo]] having, in its body, a line saying:

subscribe recode-announce

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If you rather want to participate actively in discussions, pretesting and development for Recode, do just as above, but this time, use:

subscribe recode-forum

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The [[https://github.com/pinard/Recode][Git repository]] for Recode gives access, through the magic of Git and GitHub, to all distribution releases, would they be actual or past, pretest or official, as well as individual files.

Please /do not/ widely redistribute releases having a letter after the version numbers, as these are meant for pretesting only, and might not be stable enough for other usages.

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** Notes for version 3.7-beta2 Here are a few notes related to the beta2 pre-test release for the incoming Recode 3.7. I publish it to ease later exchanges of patches with testers.

** Notes for version 3.7-beta1 The beta 1 pre-test release for the incoming Recode 3.7 has been made available for those needing it right away. While it solves some serious bugs and portability problems, others are meant to be addressed only in later pre-tests. In particular, none of charset or surface issues, user requests, and various suggestions appear in this pre-test, and will not either in later pretests, until all real show-stoppers are solved first. So this is in no way a candidate for a Recode 3.7 release.

The test suite is worth more comments:

** Non-Unix ports Please [[mailto:recode-bugs@iro.umontreal.ca][inform us]] if you are aware of various ports to non-Unix systems not listed here, or for corrections. Please provide the goal system, a complete and stable URL, the maintainer name and address, the Recode version used as a base, and your comments.

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** In a hurry? You may then try:

git clone https://github.com/pinard/Recode.git cd Recode sh after-git.sh ./configure make make install

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More fine-grained instructions follow.

** Prerequisites Simple installation of Recode requires the usual tools and facilities as those needed for most GNU packages. If not already bundled with your system, you also need to pre-install [[http://www.python.org][Python]], version 2.2 or better.

It is also convenient to have some iconv library already present on your system, this much extends Recode capabilities, especially in the area of Asiatic character sets. GNU libc, as found on Linux systems and a few others, already has such an iconv library. Otherwise, you might consider pre-installing the [[http://www.gnu.org/software/libiconv/][portable libiconv]], written by Bruno Haible.

** Getting a release Source files and various distributions (either latest, prestest, or archive) are available through [[https://github.com/pinard/Recode/][GitHub]].

File timestamps after checkout may trigger Make difficulties. As a way to avoid these, from the top level of the distribution, execute =sh after-patch.sh= before configuring. If you miss either sh or GNU touch, try =python after-patch.py= instead.

** Configure options Once you have an unpacked distribution, see files:

|-------------+------------------------------------------------| | File name | Description | |-------------+------------------------------------------------| | =ABOUT-NLS= | how to customise this program to your language | | =COPYING= | copying conditions for the program | | =COPYING.LIB= | copying conditions for the library | | =INSTALL= | compilation and installation instructions | | =NEWS= | major changes in the current release | | =THANKS= | partial list of contributors | |-------------+------------------------------------------------|

Besides those configure options documented in files =INSTALL= and =ABOUT-NLS=, a few extra options may be accepted after =./configure=:

** Installation hints Here are a few hints which might help installing Recode on some systems. Many may be applied by temporary presetting environment variables while calling =./configure=. File =INSTALL= explains this.

** Maintenance tools Beyond the usual Unix programs needed for configuring and installing any GNU package, you need Cython, Flex and Python to achieve simple modifications to Recode.

For more encompassing modifications, you might also need recent versions of Autoconf, automake, Flex, Gettext, Help2man, libtool, m4, GNU Make, Perl, tar and wget. Just make sure you install m4 before Autoconf, and Perl before automake or Help2man. You may also choose to establish a link in your build =doc/= directory, as explained within =doc/Makemore=.

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** Motivation Recode is due for a major ovehaul. My plan is to end the 3.x series of this package, rather aiming 4.0 as a major internal rewrite.

For one thing, I want to explore some new avenues. It does not seem natural anymore, to me at least, using C code for exploring or prototyping new ideas requiring complex internal structures: encompassing changes are stretchy, work overhead is just too high. I want to add a run-time dependency between Recode and Python, with the admitted goal of shifting the internals of Recode from C to Python.

Another thing is that Recode should reuse more of the work of many competent people in the recoding area. I was brought into the business of character set conversion issues by a random set of coincidences and needs, but have never been a character set specialist myself. I rely on users to help me sketch what needs to be done. There are other tools and other maintainers who address these matters more competently than me. Recode might well rely on their work and better concentrate on user functionalities and on an overall picture.

For experimenting what Recode might become and experimenting new concepts more easily, I created a subsidiary and standalone Python project named [[https://github.com/pinard/Recodec][Recodec]], which reproduces a good part of Recode functionality. My goal is now to merge Recodec back into Recode soon, rather than slowly stretching the distance between Recode and Recodec. Recode is going to be a mix of Python, C and either Pyrex or Cython.

** Overall plan The release 3.6 for Recode was likely the last in the 3.x series. As there is still a long way before 4.0 gets ready, and /especially/ because some of my good collaborators insisted that I do so, there will likely be other Recode 3.X releases on the way to 4.0, at least to provide a selection of user-contributed patches. Also, the next releases of Recode will progressively implement the base mechanics for the transition, through a list of development steps similar to the following. By principle, the implementation should be working and usable at each devewlopment step. Moreover, for better maintainability, refactoring shall occur all along the way.

I'll likely select Cython over Pyrex, the main arguments being Unicode, Python 3 and pragmatic support, and a wide and active user base. Pyrex, the inspiration behind Cython, is amazingly well thought; I stay really admirative and grateful for Greg Ewing's work.

I once thought about resorting to kludges, within a Python API interface, so the Python interpreter would not be required at all at run-time. Today, I doubt this is doable in practice, or that the implied restrictions on Cython code would be bearable. By the time, I may come to think that this is not worth the effort, anyway.

** Speed and memory So far, Recode has always been oriented towards some generality in specifications, combined with good execution speed. Generality is granted through providing recoding steps either as tables or fuller algorithms expressed as C code. Speed surely results from careful C coding of individual steps, and using Flex for more difficult recognition problems. Speed also comes from the monolithic design of a single Python-free, big executable executable holding all tables at once, relying on system paging instead of run-time opening of external data files.

Rewriting a character shuffling engine in Python is going to have consequences on both speed and memory. Python is inherently much slower than C for such problems, and program startup requires many disk accesses to load all required modules. The size of the Python interpreter is not negligible, yet Recode is not small as it stands.

Depending on how to declare things and the way to code on the Cython side, by relying less on the Python library, one may have some control over the compromise between speed and ease. With enough discipline, resisting the temptation to use many Python facilities, one can displace the equilibrium. I once dreamed of many stub or minimal routines for representing the Python library to the point of avoiding it, yet I now think it would imply too stringent limitations.

After much hesitation, I merely /decided/ that the slowdown is bearable! It was fairly tedious to make encompassing structural changes in the C version of Recode. Such changes are going to be significantly easier in Python. This might translate into shorter development cycles.

** Planned differences Whenever the Python library offers a charset or a surface which Recode also has, the Python library codec is used. In some cases, this introduces differences, those will have to be resolved one by one, either by accepting that the Python library does better, getting the Python team to improve some codecs, or overriding these from Recodec.

Other differences may occur, especially in the Asian charset area, from the fact libiconv, GNU libc recoding facilities, and various contributors to the Python codecs project, do not fully agree on how things should be done. Recodec is likely to offer configuration mechanisms to choose among various possibilities, but will not likely attempt to rule out who is right and who is wrong! ☺

Issues about reversibility and canonicity, which were much present in Recode 3.X, are fading out. While some of these were moderately easy to implement, other cases stayed pending as fairly difficult to solve without a significant loss of efficiency. I think these issues are better abandoned than forever kept as half-hearted and not wholly dependable. Any user concerned about such things might try the reverse coding to find out if the original file is recoverable, some new option might automate a (costly) reversibility test.

One drawback of the whole move is that the Global Interpreter Lock in Python gets in the way of parallel execution of the code. This would have been more of a concern if GNU libc recoding facilities were relying on the Recode library, but as things stand by now, I'm guessing that users will not be much impacted in practice.

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** Documentation - IETF references

** Programs - libiconv :: This comprehensive [[http://www.gnu.org/software/libiconv/][charset converter library]], by [[mailto:haible@ilog.fr][Bruno

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Haible]], revolves around Unicode, and support Asian encodings among many others. Even Recode uses it!

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