MirOS Manual: enc2xs(1)


ENC2XS(1)       Perl Programmers Reference Guide        ENC2XS(1)

NAME

     enc2xs -- Perl Encode Module Generator

SYNOPSIS

       enc2xs -[options]
       enc2xs -M ModName mapfiles...
       enc2xs -C

DESCRIPTION

     enc2xs builds a Perl extension for use by Encode from either
     Unicode Character Mapping files (.ucm) or Tcl Encoding Files
     (.enc). Besides being used internally during the build pro-
     cess of the Encode module, you can use enc2xs to add your
     own encoding to perl. No knowledge of XS is necessary.

Quick Guide

     If you want to know as little about Perl as possible but
     need to add a new encoding, just read this chapter and for-
     get the rest.

     0.  Have a .ucm file ready.  You can get it from somewhere
         or you can write your own from scratch or you can grab
         one from the Encode distribution and customize it.  For
         the UCM format, see the next Chapter.  In the example
         below, I'll call my theoretical encoding myascii,
         defined in my.ucm.  "$" is a shell prompt.

           $ ls -F
           my.ucm

     1.  Issue a command as follows;

           $ enc2xs -M My my.ucm
           generating Makefile.PL
           generating My.pm
           generating README
           generating Changes

         Now take a look at your current directory.  It should
         look like this.

           $ ls -F
           Makefile.PL   My.pm         my.ucm        t/

         The following files were created.

           Makefile.PL - MakeMaker script
           My.pm       - Encode submodule
           t/My.t      - test file

         1.1.
             If you want *.ucm installed together with the

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             modules, do as follows;

               $ mkdir Encode
               $ mv *.ucm Encode
               $ enc2xs -M My Encode/*ucm

     2.  Edit the files generated.  You don't have to if you have
         no time AND no intention to give it to someone else.
         But it is a good idea to edit the pod and to add more
         tests.

     3.  Now issue a command all Perl Mongers love:

           $ perl Makefile.PL
           Writing Makefile for Encode::My

     4.  Now all you have to do is make.

           $ make
           cp My.pm blib/lib/Encode/My.pm
           /usr/local/bin/perl /usr/local/bin/enc2xs -Q -O \
             -o encode_t.c -f encode_t.fnm
           Reading myascii (myascii)
           Writing compiled form
           128 bytes in string tables
           384 bytes (75%) saved spotting duplicates
           1 bytes (0.775%) saved using substrings
           ....
           chmod 644 blib/arch/auto/Encode/My/My.bs
           $

         The time it takes varies depending on how fast your
         machine is and how large your encoding is.  Unless you
         are working on something big like euc-tw, it won't take
         too long.

     5.  You can "make install" already but you should test
         first.

           $ make test
           PERL_DL_NONLAZY=1 /usr/local/bin/perl -Iblib/arch -Iblib/lib \
             -e 'use Test::Harness  qw(&runtests $verbose); \
             $verbose=0; runtests @ARGV;' t/*.t
           t/My....ok
           All tests successful.
           Files=1, Tests=2,  0 wallclock secs
            ( 0.09 cusr + 0.01 csys = 0.09 CPU)

     6.  If you are content with the test result, just "make
         install"

     7.  If you want to add your encoding to Encode's demand-

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         loading list (so you don't have to "use
         Encode::YourEncoding"), run

           enc2xs -C

         to update Encode::ConfigLocal, a module that controls
         local settings. After that, "use Encode;" is enough to
         load your encodings on demand.

The Unicode Character Map

     Encode uses the Unicode Character Map (UCM) format for
     source character mappings.  This format is used by IBM's ICU
     package and was adopted by Nick Ing-Simmons for use with the
     Encode module.  Since UCM is more flexible than Tcl's Encod-
     ing Map and far more user-friendly, this is the recommended
     formet for Encode now.

     A UCM file looks like this.

       #
       # Comments
       #
       <code_set_name> "US-ascii" # Required
       <code_set_alias> "ascii"   # Optional
       <mb_cur_min> 1             # Required; usually 1
       <mb_cur_max> 1             # Max. # of bytes/char
       <subchar> \x3F             # Substitution char
       #
       CHARMAP
       <U0000> \x00 |0 # <control>
       <U0001> \x01 |0 # <control>
       <U0002> \x02 |0 # <control>
       ....
       <U007C> \x7C |0 # VERTICAL LINE
       <U007D> \x7D |0 # RIGHT CURLY BRACKET
       <U007E> \x7E |0 # TILDE
       <U007F> \x7F |0 # <control>
       END CHARMAP

     +   Anything that follows "#" is treated as a comment.

     +   The header section continues until a line containing the
         word CHARMAP. This section has a form of <keyword>
         value, one pair per line.  Strings used as values must
         be quoted. Barewords are treated as numbers.  \xXX
         represents a byte.

         Most of the keywords are self-explanatory. subchar means
         substitution character, not subcharacter.  When you
         decode a Unicode sequence to this encoding but no match-
         ing character is found, the byte sequence defined here
         will be used.  For most cases, the value here is \x3F;

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         in ASCII, this is a question mark.

     +   CHARMAP starts the character map section.  Each line has
         a form as follows:

           <UXXXX> \xXX.. |0 # comment
             ^     ^      ^
             |     |      +- Fallback flag
             |     +-------- Encoded byte sequence
             +-------------- Unicode Character ID in hex

         The format is roughly the same as a header section
         except for the fallback flag: | followed by 0..3.   The
         meaning of the possible values is as follows:

         |0  Round trip safe.  A character decoded to Unicode
             encodes back to the same byte sequence.  Most char-
             acters have this flag.

         |1  Fallback for unicode -> encoding.  When seen, enc2xs
             adds this character for the encode map only.

         |2  Skip sub-char mapping should there be no code point.

         |3  Fallback for encoding -> unicode.  When seen, enc2xs
             adds this character for the decode map only.

     +   And finally, END OF CHARMAP ends the section.

     When you are manually creating a UCM file, you should copy
     ascii.ucm or an existing encoding which is close to yours,
     rather than write your own from scratch.

     When you do so, make sure you leave at least U0000 to U0020
     as is, unless your environment is EBCDIC.

     CAVEAT: not all features in UCM are implemented.  For exam-
     ple, icu:state is not used.  Because of that, you need to
     write a perl module if you want to support algorithmical
     encodings, notably the ISO-2022 series.  Such modules
     include Encode::JP::2022_JP, Encode::KR::2022_KR, and
     Encode::TW::HZ.

     Coping with duplicate mappings

     When you create a map, you SHOULD make your mappings round-
     trip safe. That is, "encode('your-encoding',
     decode('your-encoding', $data)) eq $data" stands for all
     characters that are marked as "|0".  Here is how to make
     sure:

     +   Sort your map in Unicode order.

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     +   When you have a duplicate entry, mark either one with
         '|1' or '|3'.

     +   And make sure the '|1' or '|3' entry FOLLOWS the '|0'
         entry.

     Here is an example from big5-eten.

       <U2550> \xF9\xF9 |0
       <U2550> \xA2\xA4 |3

     Internally Encoding -> Unicode and Unicode -> Encoding Map
     looks like this;

       E to U               U to E
       --------------------------------------
       \xF9\xF9 => U2550    U2550 => \xF9\xF9
       \xA2\xA4 => U2550

     So it is round-trip safe for \xF9\xF9.  But if the line
     above is upside down, here is what happens.

       E to U               U to E
       --------------------------------------
       \xA2\xA4 => U2550    U2550 => \xF9\xF9
       (\xF9\xF9 => U2550 is now overwritten!)

     The Encode package comes with ucmlint, a crude but suffi-
     cient utility to check the integrity of a UCM file.  Check
     under the Encode/bin directory for this.

     When in doubt, you can use ucmsort, yet another utility
     under Encode/bin directory.

Bookmarks

     +   ICU Home Page <http://oss.software.ibm.com/icu/>

     +   ICU Character Mapping Tables
         <http://oss.software.ibm.com/icu/charset/>

     +   ICU:Conversion Data
         <http://oss.software.ibm.com/icu/userguide/conversion-data.html>

SEE ALSO

     Encode, perlmod, perlpod

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