1 package Encode::Unicode;
5 no warnings 'redefine';
7 our $VERSION = do { my @r = (q$Revision: 2.2 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r };
10 XSLoader::load(__PACKAGE__,$VERSION);
13 # Object Generator 8 transcoders all at once!
18 our %BOM_Unknown = map {$_ => 1} qw(UTF-16 UTF-32);
20 for my $name (qw(UTF-16 UTF-16BE UTF-16LE
21 UTF-32 UTF-32BE UTF-32LE
24 my ($size, $endian, $ucs2, $mask);
25 $name =~ /^(\w+)-(\d+)(\w*)$/o;
26 if ($ucs2 = ($1 eq 'UCS')){
31 $endian = ($3 eq 'BE') ? 'n' : ($3 eq 'LE') ? 'v' : '' ;
32 $size == 4 and $endian = uc($endian);
34 $Encode::Encoding{$name} =
43 use base qw(Encode::Encoding);
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.
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
56 *decode = \&decode_xs;
57 *encode = \&encode_xs;
64 Encode::Unicode -- Various Unicode Transformation Formats
70 use Encode qw/encode decode/;
71 $ucs2 = encode("UCS-2BE", $utf8);
72 $utf8 = decode("UCS-2BE", $ucs2);
76 This module implements all Character Encoding Schemes of Unicode that
77 are officially documented by Unicode Consortium (except, of course,
78 for UTF-8, which is a native format in perl).
82 =item L<http://www.unicode.org/glossary/> says:
84 I<Character Encoding Scheme> A character encoding form plus byte
85 serialization. There are Seven character encoding schemes in Unicode:
86 UTF-8, UTF-16, UTF-16BE, UTF-16LE, UTF-32 (UCS-4), UTF-32BE (UCS-4BE) and
87 UTF-32LE (UCS-4LE), and UTF-7.
89 Since UTF-7 is a 7-bit (re)encoded version of UTF-16BE, It is not part of
90 Unicode's Character Encoding Scheme. It is separately implemented in
91 Encode::Unicode::UTF7. For details see L<Encode::Unicode::UTF7>.
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 ---------------+-----------------+------------------------------
111 =head1 Size, Endianness, and BOM
113 You can categorize these CES by 3 criteria: size of each character,
114 endianness, and Byte Order Mark.
118 UCS-2 is a fixed-length encoding with each character taking 16 bits.
119 It B<does not> support I<surrogate pairs>. When a surrogate pair
120 is encountered during decode(), its place is filled with \x{FFFD}
121 if I<CHECK> is 0, or the routine croaks if I<CHECK> is 1. When a
122 character whose ord value is larger than 0xFFFF is encountered,
123 its place is filled with \x{FFFD} if I<CHECK> is 0, or the routine
124 croaks if I<CHECK> is 1.
126 UTF-16 is almost the same as UCS-2 but it supports I<surrogate pairs>.
127 When it encounters a high surrogate (0xD800-0xDBFF), it fetches the
128 following low surrogate (0xDC00-0xDFFF) and C<desurrogate>s them to
129 form a character. Bogus surrogates result in death. When \x{10000}
130 or above is encountered during encode(), it C<ensurrogate>s them and
131 pushes the surrogate pair to the output stream.
133 UTF-32 (UCS-4) is a fixed-length encoding with each character taking 32 bits.
134 Since it is 32-bit, there is no need for I<surrogate pairs>.
138 The first (and now failed) goal of Unicode was to map all character
139 repertoires into a fixed-length integer so that programmers are happy.
140 Since each character is either a I<short> or I<long> in C, you have to
141 pay attention to the endianness of each platform when you pass data
144 Anything marked as BE is Big Endian (or network byte order) and LE is
145 Little Endian (aka VAX byte order). For anything not marked either
146 BE or LE, a character called Byte Order Mark (BOM) indicating the
147 endianness is prepended to the string.
149 CAVEAT: Though BOM in utf8 (\xEF\xBB\xBF) is valid, it is meaningless
150 and as of this writing Encode suite just leave it as is (\x{FeFF}).
154 =item BOM as integer when fetched in network byte order
157 -------------------------
160 -------------------------
164 This modules handles the BOM as follows.
170 When BE or LE is explicitly stated as the name of encoding, BOM is
171 simply treated as a normal character (ZERO WIDTH NO-BREAK SPACE).
175 When BE or LE is omitted during decode(), it checks if BOM is at the
176 beginning of the string; if one is found, the endianness is set to
177 what the BOM says. If no BOM is found, the routine dies.
181 When BE or LE is omitted during encode(), it returns a BE-encoded
182 string with BOM prepended. So when you want to encode a whole text
183 file, make sure you encode() the whole text at once, not line by line
184 or each line, not file, will have a BOM prepended.
188 C<UCS-2> is an exception. Unlike others, this is an alias of UCS-2BE.
189 UCS-2 is already registered by IANA and others that way.
193 =head1 Surrogate Pairs
195 To say the least, surrogate pairs were the biggest mistake of the
196 Unicode Consortium. But according to the late Douglas Adams in I<The
197 Hitchhiker's Guide to the Galaxy> Trilogy, C<In the beginning the
198 Universe was created. This has made a lot of people very angry and
199 been widely regarded as a bad move>. Their mistake was not of this
200 magnitude so let's forgive them.
202 (I don't dare make any comparison with Unicode Consortium and the
203 Vogons here ;) Or, comparing Encode to Babel Fish is completely
204 appropriate -- if you can only stick this into your ear :)
206 Surrogate pairs were born when the Unicode Consortium finally
207 admitted that 16 bits were not big enough to hold all the world's
208 character repertoires. But they already made UCS-2 16-bit. What
211 Back then, the range 0xD800-0xDFFF was not allocated. Let's split
212 that range in half and use the first half to represent the C<upper
213 half of a character> and the second half to represent the C<lower
214 half of a character>. That way, you can represent 1024 * 1024 =
215 1048576 more characters. Now we can store character ranges up to
216 \x{10ffff} even with 16-bit encodings. This pair of half-character is
217 now called a I<surrogate pair> and UTF-16 is the name of the encoding
220 Here is a formula to ensurrogate a Unicode character \x{10000} and
223 $hi = ($uni - 0x10000) / 0x400 + 0xD800;
224 $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
228 $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
230 Note this move has made \x{D800}-\x{DFFF} into a forbidden zone but
231 perl does not prohibit the use of characters within this range. To perl,
232 every one of \x{0000_0000} up to \x{ffff_ffff} (*) is I<a character>.
234 (*) or \x{ffff_ffff_ffff_ffff} if your perl is compiled with 64-bit
237 =head1 Error Checking
239 Unlike most encodings which accept various ways to handle errors,
240 Unicode encodings simply croaks.
242 % perl -MEncode -e '$_ = "\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.
249 Unlike other encodings where mappings are not one-to-one against
250 Unicode, UTFs are supposed to map 100% against one another. So Encode
251 is more strict on UTFs.
253 Consider that "division by zero" of Encode :)
257 L<Encode>, L<Encode::Unicode::UTF7>, L<http://www.unicode.org/glossary/>,
258 L<http://www.unicode.org/unicode/faq/utf_bom.html>,
260 RFC 2781 L<http://rfc.net/rfc2781.html>,
262 The whole Unicode standard L<http://www.unicode.org/unicode/uni2book/u2.html>
264 Ch. 15, pp. 403 of C<Programming Perl (3rd Edition)>
265 by Larry Wall, Tom Christiansen, Jon Orwant;
266 O'Reilly & Associates; ISBN 0-596-00027-8