1package Encode::Unicode;
2
3use strict;
4use warnings;
5no warnings 'redefine';
6
7our $VERSION = do { my @r = (q$Revision: 2.2 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r };
8
9use XSLoader;
10XSLoader::load(__PACKAGE__,$VERSION);
11
12#
13# Object Generator 8 transcoders all at once!
14#
15
16require Encode;
17
18our %BOM_Unknown = map {$_ => 1} qw(UTF-16 UTF-32);
19
20for my $name (qw(UTF-16 UTF-16BE UTF-16LE
21                 UTF-32 UTF-32BE UTF-32LE
22                        UCS-2BE  UCS-2LE))
23{
24    my ($size, $endian, $ucs2, $mask);
25    $name =~ /^(\w+)-(\d+)(\w*)$/o;
26    if ($ucs2 = ($1 eq 'UCS')){
27	$size = 2;
28    }else{
29	$size = $2/8;
30    }
31    $endian = ($3 eq 'BE') ? 'n' : ($3 eq 'LE') ? 'v' : '' ;
32    $size == 4 and $endian = uc($endian);
33
34    $Encode::Encoding{$name} =
35	bless {
36	       Name   =>   $name,
37	       size   =>   $size,
38	       endian => $endian,
39	       ucs2   =>   $ucs2,
40	      } => __PACKAGE__;
41}
42
43use base qw(Encode::Encoding);
44
45sub renew {
46    my $self = shift;
47    $BOM_Unknown{$self->name} or return $self;
48    my $clone = bless { %$self } => ref($self);
49    $clone->{renewed}++; # so the caller knows it is renewed.
50    return $clone;
51}
52
53# There used to be a perl implemntation of (en|de)code but with
54# XS version is ripe, perl version is zapped for optimal speed
55
56*decode = \&decode_xs;
57*encode = \&encode_xs;
58
591;
60__END__
61
62=head1 NAME
63
64Encode::Unicode -- Various Unicode Transformation Formats
65
66=cut
67
68=head1 SYNOPSIS
69
70    use Encode qw/encode decode/;
71    $ucs2 = encode("UCS-2BE", $utf8);
72    $utf8 = decode("UCS-2BE", $ucs2);
73
74=head1 ABSTRACT
75
76This module implements all Character Encoding Schemes of Unicode that
77are officially documented by Unicode Consortium (except, of course,
78for UTF-8, which is a native format in perl).
79
80=over 4
81
82=item L<http://www.unicode.org/glossary/> says:
83
84I<Character Encoding Scheme> A character encoding form plus byte
85serialization. There are Seven character encoding schemes in Unicode:
86UTF-8, UTF-16, UTF-16BE, UTF-16LE, UTF-32 (UCS-4), UTF-32BE (UCS-4BE) and
87UTF-32LE (UCS-4LE), and UTF-7.
88
89Since UTF-7 is a 7-bit (re)encoded version of UTF-16BE, It is not part of
90Unicode's Character Encoding Scheme.  It is separately implemented in
91Encode::Unicode::UTF7.  For details see L<Encode::Unicode::UTF7>.
92
93=item Quick Reference
94
95                Decodes from ord(N)           Encodes chr(N) to...
96       octet/char BOM S.P d800-dfff  ord > 0xffff     \x{1abcd} ==
97  ---------------+-----------------+------------------------------
98  UCS-2BE	2   N   N  is bogus                  Not Available
99  UCS-2LE       2   N   N     bogus                  Not Available
100  UTF-16      2/4   Y   Y  is   S.P           S.P            BE/LE
101  UTF-16BE    2/4   N   Y       S.P           S.P    0xd82a,0xdfcd
102  UTF-16LE	2   N   Y       S.P           S.P    0x2ad8,0xcddf
103  UTF-32	4   Y   -  is bogus         As is            BE/LE
104  UTF-32BE	4   N   -     bogus         As is       0x0001abcd
105  UTF-32LE	4   N   -     bogus         As is       0xcdab0100
106  UTF-8       1-4   -   -     bogus   >= 4 octets   \xf0\x9a\af\8d
107  ---------------+-----------------+------------------------------
108
109=back
110
111=head1 Size, Endianness, and BOM
112
113You can categorize these CES by 3 criteria:  size of each character,
114endianness, and Byte Order Mark.
115
116=head2 by size
117
118UCS-2 is a fixed-length encoding with each character taking 16 bits.
119It B<does not> support I<surrogate pairs>.  When a surrogate pair
120is encountered during decode(), its place is filled with \x{FFFD}
121if I<CHECK> is 0, or the routine croaks if I<CHECK> is 1.  When a
122character whose ord value is larger than 0xFFFF is encountered,
123its place is filled with \x{FFFD} if I<CHECK> is 0, or the routine
124croaks if I<CHECK> is 1.
125
126UTF-16 is almost the same as UCS-2 but it supports I<surrogate pairs>.
127When it encounters a high surrogate (0xD800-0xDBFF), it fetches the
128following low surrogate (0xDC00-0xDFFF) and C<desurrogate>s them to
129form a character.  Bogus surrogates result in death.  When \x{10000}
130or above is encountered during encode(), it C<ensurrogate>s them and
131pushes the surrogate pair to the output stream.
132
133UTF-32 (UCS-4) is a fixed-length encoding with each character taking 32 bits.
134Since it is 32-bit, there is no need for I<surrogate pairs>.
135
136=head2 by endianness
137
138The first (and now failed) goal of Unicode was to map all character
139repertoires into a fixed-length integer so that programmers are happy.
140Since each character is either a I<short> or I<long> in C, you have to
141pay attention to the endianness of each platform when you pass data
142to one another.
143
144Anything marked as BE is Big Endian (or network byte order) and LE is
145Little Endian (aka VAX byte order).  For anything not marked either
146BE or LE, a character called Byte Order Mark (BOM) indicating the
147endianness is prepended to the string.
148
149CAVEAT: Though BOM in utf8 (\xEF\xBB\xBF) is valid, it is meaningless
150and as of this writing Encode suite just leave it as is (\x{FeFF}).
151
152=over 4
153
154=item BOM as integer when fetched in network byte order
155
156              16         32 bits/char
157  -------------------------
158  BE      0xFeFF 0x0000FeFF
159  LE      0xFFeF 0xFFFe0000
160  -------------------------
161
162=back
163
164This modules handles the BOM as follows.
165
166=over 4
167
168=item *
169
170When BE or LE is explicitly stated as the name of encoding, BOM is
171simply treated as a normal character (ZERO WIDTH NO-BREAK SPACE).
172
173=item *
174
175When BE or LE is omitted during decode(), it checks if BOM is at the
176beginning of the string; if one is found, the endianness is set to
177what the BOM says.  If no BOM is found, the routine dies.
178
179=item *
180
181When BE or LE is omitted during encode(), it returns a BE-encoded
182string with BOM prepended.  So when you want to encode a whole text
183file, make sure you encode() the whole text at once, not line by line
184or each line, not file, will have a BOM prepended.
185
186=item *
187
188C<UCS-2> is an exception.  Unlike others, this is an alias of UCS-2BE.
189UCS-2 is already registered by IANA and others that way.
190
191=back
192
193=head1 Surrogate Pairs
194
195To say the least, surrogate pairs were the biggest mistake of the
196Unicode Consortium.  But according to the late Douglas Adams in I<The
197Hitchhiker's Guide to the Galaxy> Trilogy, C<In the beginning the
198Universe was created. This has made a lot of people very angry and
199been widely regarded as a bad move>.  Their mistake was not of this
200magnitude so let's forgive them.
201
202(I don't dare make any comparison with Unicode Consortium and the
203Vogons here ;)  Or, comparing Encode to Babel Fish is completely
204appropriate -- if you can only stick this into your ear :)
205
206Surrogate pairs were born when the Unicode Consortium finally
207admitted that 16 bits were not big enough to hold all the world's
208character repertoires.  But they already made UCS-2 16-bit.  What
209do we do?
210
211Back then, the range 0xD800-0xDFFF was not allocated.  Let's split
212that range in half and use the first half to represent the C<upper
213half of a character> and the second half to represent the C<lower
214half of a character>.  That way, you can represent 1024 * 1024 =
2151048576 more characters.  Now we can store character ranges up to
216\x{10ffff} even with 16-bit encodings.  This pair of half-character is
217now called a I<surrogate pair> and UTF-16 is the name of the encoding
218that embraces them.
219
220Here is a formula to ensurrogate a Unicode character \x{10000} and
221above;
222
223  $hi = ($uni - 0x10000) / 0x400 + 0xD800;
224  $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
225
226And to desurrogate;
227
228 $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
229
230Note this move has made \x{D800}-\x{DFFF} into a forbidden zone but
231perl does not prohibit the use of characters within this range.  To perl,
232every one of \x{0000_0000} up to \x{ffff_ffff} (*) is I<a character>.
233
234  (*) or \x{ffff_ffff_ffff_ffff} if your perl is compiled with 64-bit
235  integer support!
236
237=head1 Error Checking
238
239Unlike most encodings which accept various ways to handle errors,
240Unicode encodings simply croaks.
241
242  % perl -MEncode -e '$_ = "\xfe\xff\xd8\xd9\xda\xdb\0\n"' \
243         -e 'Encode::from_to($_, "utf16","shift_jis", 0); print'
244  UTF-16:Malformed LO surrogate d8d9 at /path/to/Encode.pm line 184.
245  % perl -MEncode -e '$a = "BOM missing"' \
246         -e ' Encode::from_to($a, "utf16", "shift_jis", 0); print'
247  UTF-16:Unrecognised BOM 424f at /path/to/Encode.pm line 184.
248
249Unlike other encodings where mappings are not one-to-one against
250Unicode, UTFs are supposed to map 100% against one another.  So Encode
251is more strict on UTFs.
252
253Consider that "division by zero" of Encode :)
254
255=head1 SEE ALSO
256
257L<Encode>, L<Encode::Unicode::UTF7>, L<http://www.unicode.org/glossary/>,
258L<http://www.unicode.org/unicode/faq/utf_bom.html>,
259
260RFC 2781 L<http://rfc.net/rfc2781.html>,
261
262The whole Unicode standard L<http://www.unicode.org/unicode/uni2book/u2.html>
263
264Ch. 15, pp. 403 of C<Programming Perl (3rd Edition)>
265by Larry Wall, Tom Christiansen, Jon Orwant;
266O'Reilly & Associates; ISBN 0-596-00027-8
267
268=cut
269