## 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 dur
           ing the build process 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
           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 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 mod
                   ules, do as follows;

           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 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-
               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 Encoding Map and far more user-friendly, this is the
           recommended formet for Encode now.
             <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
               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 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
                   characters 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.

           example, icu:state is not used.  Because of that, you need
           to write a perl module if you want to support algorithmi
           cal 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.

           ·   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.

## Bookmarks

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

           ·   ICU Character Mapping Tables <http://oss.soft
               ware.ibm.com/icu/charset/>