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 internally used during the build process of Encode module, you can use enc2xs to add your own encoding to perl. No knowledge on XS is necessary.

Quick Guide

If what you want to know as little about Perl possible but needs to add 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 write your own from scratch or you can grab one from Encode distribution and customize. For UCM format, see the next Chapter. In the example below, I'll call my theoretical encoding myascii, defined inmy.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 are created.

Makefle.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 no intention to give it to someone else. But it is a good idea to edit pod and add more tests.

3.

Now issue a command all Perl Mongers love;

$ perl5.7.3 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 (25%) saved spotting duplicates
1 bytes (99.2%) saved using substrings
....
chmod 644 blib/arch/auto/Encode/My/My.bs
$

The time it takes varies 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 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) for source character mappings. This format is used by ICU package of IBM and adopted by Nick Ing-Simmons. Since UCM is more flexible than Tcl's Encoding Map and far more user-friendly, This is the recommended formet for Encode now.

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 comments.

• The header section continues until CHARMAP. This section Has a form of <keyword> value, one at a line. For a value, strings 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 matching character is found, the byte sequence 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 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 fallback flag. It is | followed by 0..3. And their meaning as follows

  |0

  Round trip safe. A character decoded to Unicode encodes back to the same byte sequence. most character belong to this.

  |1

  Fallback for unicode -> encoding. When seen, enc2xs adds this character for 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 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 existing encoding which is close to yours 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 on EBCDIC.

CAVEAT: not all features in UCM are implemented. For example, icu:state is not used. Because of that, you need to write a perl module if you want to support algorithmical encodings, notablly 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.

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

• And make sure '|1' or '|3' FOLLOWS '|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 sufficient utility to check the integrity of ucm file. Check under Encode/bin directory for this.

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

cpanm Encode

perl -MCPAN -e shell
install Encode