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1 | package Encode::Unicode; |
2 | |
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3 | use strict; |
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4 | use warnings; |
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5 | no warnings 'redefine'; |
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6 | |
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7 | our $VERSION = do { my @r = (q$Revision: 2.2 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r }; |
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8 | |
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9 | use XSLoader; |
10 | XSLoader::load(__PACKAGE__,$VERSION); |
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11 | |
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12 | # |
13 | # Object Generator 8 transcoders all at once! |
14 | # |
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15 | |
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16 | require Encode; |
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17 | |
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18 | our %BOM_Unknown = map {$_ => 1} qw(UTF-16 UTF-32); |
19 | |
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20 | for my $name (qw(UTF-16 UTF-16BE UTF-16LE |
21 | UTF-32 UTF-32BE UTF-32LE |
22 | UCS-2BE UCS-2LE)) |
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23 | { |
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24 | my ($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; |
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30 | } |
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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, |
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40 | } => __PACKAGE__; |
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41 | } |
42 | |
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43 | use base qw(Encode::Encoding); |
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44 | |
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45 | sub renew { |
46 | my $self = shift; |
47 | $BOM_Unknown{$self->name} or return $self; |
48 | my $clone = bless { %$self } => ref($self); |
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49 | $clone->{renewed}++; # so the caller knows it is renewed. |
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50 | return $clone; |
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51 | } |
52 | |
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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 |
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55 | |
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56 | *decode = \&decode_xs; |
57 | *encode = \&encode_xs; |
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58 | |
59 | 1; |
60 | __END__ |
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61 | |
62 | =head1 NAME |
63 | |
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64 | Encode::Unicode -- Various Unicode Transformation Formats |
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65 | |
66 | =cut |
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67 | |
68 | =head1 SYNOPSIS |
69 | |
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70 | use Encode qw/encode decode/; |
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71 | $ucs2 = encode("UCS-2BE", $utf8); |
72 | $utf8 = decode("UCS-2BE", $ucs2); |
73 | |
74 | =head1 ABSTRACT |
75 | |
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). |
79 | |
80 | =over 4 |
81 | |
82 | =item L<http://www.unicode.org/glossary/> says: |
83 | |
84 | I<Character Encoding Scheme> A character encoding form plus byte |
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85 | serialization. There are Seven character encoding schemes in Unicode: |
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86 | UTF-8, UTF-16, UTF-16BE, UTF-16LE, UTF-32 (UCS-4), UTF-32BE (UCS-4BE) and |
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87 | UTF-32LE (UCS-4LE), and UTF-7. |
88 | |
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>. |
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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 |
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104 | UTF-32BE 4 N - bogus As is 0x0001abcd |
105 | UTF-32LE 4 N - bogus As is 0xcdab0100 |
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106 | UTF-8 1-4 - - bogus >= 4 octets \xf0\x9a\af\8d |
107 | ---------------+-----------------+------------------------------ |
108 | |
109 | =back |
110 | |
111 | =head1 Size, Endianness, and BOM |
112 | |
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113 | You can categorize these CES by 3 criteria: size of each character, |
114 | endianness, and Byte Order Mark. |
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115 | |
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116 | =head2 by size |
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117 | |
118 | UCS-2 is a fixed-length encoding with each character taking 16 bits. |
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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. |
125 | |
126 | UTF-16 is almost the same as UCS-2 but it supports I<surrogate pairs>. |
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127 | When it encounters a high surrogate (0xD800-0xDBFF), it fetches the |
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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. |
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132 | |
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133 | UTF-32 (UCS-4) is a fixed-length encoding with each character taking 32 bits. |
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134 | Since it is 32-bit, there is no need for I<surrogate pairs>. |
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135 | |
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136 | =head2 by endianness |
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137 | |
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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 |
142 | to one another. |
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143 | |
144 | Anything marked as BE is Big Endian (or network byte order) and LE is |
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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. |
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148 | |
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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}). |
151 | |
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152 | =over 4 |
153 | |
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154 | =item BOM as integer when fetched in network byte order |
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155 | |
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156 | 16 32 bits/char |
157 | ------------------------- |
158 | BE 0xFeFF 0x0000FeFF |
159 | LE 0xFFeF 0xFFFe0000 |
160 | ------------------------- |
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161 | |
162 | =back |
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163 | |
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164 | This modules handles the BOM as follows. |
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165 | |
166 | =over 4 |
167 | |
168 | =item * |
169 | |
170 | When BE or LE is explicitly stated as the name of encoding, BOM is |
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171 | simply treated as a normal character (ZERO WIDTH NO-BREAK SPACE). |
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172 | |
173 | =item * |
174 | |
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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. |
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178 | |
179 | =item * |
180 | |
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 |
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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. |
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185 | |
186 | =item * |
187 | |
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188 | C<UCS-2> is an exception. Unlike others, this is an alias of UCS-2BE. |
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189 | UCS-2 is already registered by IANA and others that way. |
190 | |
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191 | =back |
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192 | |
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193 | =head1 Surrogate Pairs |
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194 | |
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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. |
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201 | |
202 | (I don't dare make any comparison with Unicode Consortium and the |
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203 | Vogons here ;) Or, comparing Encode to Babel Fish is completely |
204 | appropriate -- if you can only stick this into your ear :) |
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205 | |
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206 | Surrogate pairs were born when the Unicode Consortium finally |
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207 | admitted that 16 bits were not big enough to hold all the world's |
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208 | character repertoires. But they already made UCS-2 16-bit. What |
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209 | do we do? |
210 | |
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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 |
218 | that embraces them. |
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219 | |
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220 | Here is a formula to ensurrogate a Unicode character \x{10000} and |
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221 | above; |
222 | |
223 | $hi = ($uni - 0x10000) / 0x400 + 0xD800; |
224 | $lo = ($uni - 0x10000) % 0x400 + 0xDC00; |
225 | |
226 | And to desurrogate; |
227 | |
228 | $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); |
229 | |
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230 | Note this move has made \x{D800}-\x{DFFF} into a forbidden zone but |
231 | perl does not prohibit the use of characters within this range. To perl, |
232 | every one of \x{0000_0000} up to \x{ffff_ffff} (*) is I<a character>. |
233 | |
234 | (*) or \x{ffff_ffff_ffff_ffff} if your perl is compiled with 64-bit |
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235 | integer support! |
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236 | |
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237 | =head1 Error Checking |
238 | |
239 | Unlike most encodings which accept various ways to handle errors, |
240 | Unicode encodings simply croaks. |
241 | |
242 | % perl -MEncode -e '$_ = "\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 | |
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. |
252 | |
253 | Consider that "division by zero" of Encode :) |
254 | |
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255 | =head1 SEE ALSO |
256 | |
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257 | L<Encode>, L<Encode::Unicode::UTF7>, L<http://www.unicode.org/glossary/>, |
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258 | L<http://www.unicode.org/unicode/faq/utf_bom.html>, |
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259 | |
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260 | RFC 2781 L<http://rfc.net/rfc2781.html>, |
261 | |
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262 | The whole Unicode standard L<http://www.unicode.org/unicode/uni2book/u2.html> |
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263 | |
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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 |
267 | |
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268 | =cut |