enc2xs -- Perl Encode Module Generator
enc2xs -[options]
enc2xs -M ModName mapfiles...
enc2xs -C
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 process of the Encode module, you can use
enc2xs to add your own encoding to perl. No knowledge of
XS is necessary.
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 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 (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 demandloading
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 [Toc] [Back] 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.
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> F # Substitution char
#
CHARMAP
<U0000> 0 |0 # <control>
<U0001> 1 |0 # <control>
<U0002> 2 |0 # <control>
....
<U007C> C |0 # VERTICAL LINE
<U007D> D |0 # RIGHT CURLY BRACKET
<U007E> E |0 # TILDE
<U007F> F |0 # <control>
END CHARMAP
o Anything that follows "#" is treated as a comment.
o 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. _XX
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
F; in ASCII, this is a question mark.
o CHARMAP starts the character map section. Each line
has a form as follows:
<UXXXX> .. |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.
|3 Fallback for encoding -> unicode. When seen,
enc2xs adds this character for the decode map
only.
o 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
example, 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 [Toc] [Back]
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:
o Sort your map in Unicode order.
o When you have a duplicate entry, mark either one with
'|1' or '|3'.
o And make sure the '|1' or '|3' entry FOLLOWS the '|0'
entry.
Here is an example from big5-eten.
<U2550> |0
<U2550> |3
Internally Encoding -> Unicode and Unicode -> Encoding Map
looks like this;
E to U U to E
--------------------------------------
=> U2550 U2550 => => U2550
So it is round-trip safe for But if the line
above is upside down, here is what happens.
E to U U to E
--------------------------------------
=> U2550 U2550 => (=> U2550 is now overwrit
ten!)
The Encode package comes with ucmlint, a crude but sufficient
utility to check the integrity of a UCM file. Check
under the Encode/bin directory for this.
o ICU Home Page <http://oss.software.ibm.com/icu/>
o ICU Character Mapping Tables <http://oss.soft-
ware.ibm.com/icu/charset/>
o ICU:Conversion Data <http://oss.soft-
ware.ibm.com/icu/userguide/conversion-data.html>
Encode, perlmod, perlpod
perl v5.8.5 2002-11-06 5 [ Back ] |
