Daftar Isi

• NAME
• SYNOPSIS
• DESCRIPTION
• Quick Guide
• The Unicode Character Map
  • Coping with duplicate mappings
• Bookmarks
• SEE ALSO

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 eitherUnicode Character Mapping files (.ucm) or Tcl Encoding Files (.enc).Besides being used internally during the build process of the Encodemodule, 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 toadd a new encoding, just read this chapter and forget the rest.

0.

Have a .ucm file ready. You can get it from somewhere or you can writeyour own from scratch or you can grab one from the Encode distributionand customize it. For the UCM format, see the next Chapter. In theexample below, I'll call my theoretical encoding myascii, definedin 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 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 nointention to give it to someone else. But it is a good idea to editthe 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 andhow large your encoding is. Unless you are working on something biglike 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-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 charactermappings. This format is used by IBM's ICU package and was adoptedby Nick Ing-Simmons for use with the Encode module. Since UCM ismore flexible than Tcl's Encoding Map and far more user-friendly,this is the recommended format 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 wordCHARMAP. This section has a form of <keyword> value, onepair per line. Strings used as values must be quoted. Barewords aretreated as numbers. \xXX represents a byte.

  Most of the keywords are self-explanatory. subchar meanssubstitution character, not subcharacter. When you decode a Unicodesequence to this encoding but no matching character is found, the bytesequence defined here will be used. For most cases, the value here is\x3F; in ASCII, this is a question mark.

• CHARMAP starts the character map section. Each line has a form asfollows:

    <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 thefallback flag: | followed by 0..3. The meaning of the possiblevalues is as follows:

  • |0

    Round trip safe. A character decoded to Unicode encodes back to thesame byte sequence. Most characters have this flag.

  • |1

    Fallback for unicode -> encoding. When seen, enc2xs adds thischaracter 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 thischaracter 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.ucmor an existing encoding which is close to yours, rather than writeyour own from scratch.

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

CAVEAT: not all features in UCM are implemented. For example,icu:state is not used. Because of that, you need to write a perlmodule if you want to support algorithmical encodings, notablythe 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 ishow to make sure:

• Sort your map in Unicode order.

• 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 likethis;

  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 upsidedown, 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 sufficientutility to check the integrity of a UCM file. Check under theEncode/bin directory for this.

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

Bookmarks

• ICU Home Page http://www.icu-project.org/

• ICU Character Mapping Tableshttp://site.icu-project.org/charts/charset

• ICU:Conversion Datahttp://www.icu-project.org/userguide/conversion-data.html

SEE ALSO

Encode,perlmod,perlpod