package Encode::Unicode;use strict;use warnings;no warnings 'redefine';our $VERSION = do { my @r = ( q$Revision: 2.5 $ =~ /\d+/g ); sprintf "%d." . "%02d" x $#r, @r };use XSLoader;XSLoader::load( __PACKAGE__, $VERSION );## Object Generator 8 transcoders all at once!#require Encode;our %BOM_Unknown = map { $_ => 1 } qw(UTF-16 UTF-32);for my $name (    qw(UTF-16 UTF-16BE UTF-16LE    UTF-32 UTF-32BE UTF-32LE    UCS-2BE  UCS-2LE)  ){    my ( $size, $endian, $ucs2, $mask );    $name =~ /^(\w+)-(\d+)(\w*)$/o;    if ( $ucs2 = ( $1 eq 'UCS' ) ) {        $size = 2;    }    else {        $size = $2 / 8;    }    $endian = ( $3 eq 'BE' ) ? 'n' : ( $3 eq 'LE' ) ? 'v' : '';    $size == 4 and $endian = uc($endian);    $Encode::Encoding{$name} = bless {        Name   => $name,        size   => $size,        endian => $endian,        ucs2   => $ucs2,    } => __PACKAGE__;}use base qw(Encode::Encoding);sub renew {    my $self = shift;    $BOM_Unknown{ $self->name } or return $self;    my $clone = bless {%$self} => ref($self);    $clone->{renewed}++;    # so the caller knows it is renewed.    return $clone;}# There used to be a perl implemntation of (en|de)code but with# XS version is ripe, perl version is zapped for optimal speed*decode = \&decode_xs;*encode = \&encode_xs;1;__END__=head1 NAMEEncode::Unicode -- Various Unicode Transformation Formats=cut=head1 SYNOPSIS    use Encode qw/encode decode/;     $ucs2 = encode("UCS-2BE", $utf8);    $utf8 = decode("UCS-2BE", $ucs2);=head1 ABSTRACTThis module implements all Character Encoding Schemes of Unicode thatare officially documented by Unicode Consortium (except, of course,for UTF-8, which is a native format in perl).=over 4=item L<http://www.unicode.org/glossary/> says:I<Character Encoding Scheme> A character encoding form plus byteserialization. There are Seven character encoding schemes in Unicode:UTF-8, UTF-16, UTF-16BE, UTF-16LE, UTF-32 (UCS-4), UTF-32BE (UCS-4BE) andUTF-32LE (UCS-4LE), and UTF-7.Since UTF-7 is a 7-bit (re)encoded version of UTF-16BE, It is not part ofUnicode's Character Encoding Scheme.  It is separately implemented inEncode::Unicode::UTF7.  For details see L<Encode::Unicode::UTF7>.=item Quick Reference                Decodes from ord(N)           Encodes chr(N) to...       octet/char BOM S.P d800-dfff  ord > 0xffff     \x{1abcd} ==  ---------------+-----------------+------------------------------  UCS-2BE       2   N   N  is bogus                  Not Available  UCS-2LE       2   N   N     bogus                  Not Available  UTF-16      2/4   Y   Y  is   S.P           S.P            BE/LE  UTF-16BE    2/4   N   Y       S.P           S.P    0xd82a,0xdfcd  UTF-16LE    2/4   N   Y       S.P           S.P    0x2ad8,0xcddf  UTF-32        4   Y   -  is bogus         As is            BE/LE  UTF-32BE      4   N   -     bogus         As is       0x0001abcd  UTF-32LE      4   N   -     bogus         As is       0xcdab0100  UTF-8       1-4   -   -     bogus   >= 4 octets   \xf0\x9a\af\8d  ---------------+-----------------+------------------------------=back=head1 Size, Endianness, and BOMYou can categorize these CES by 3 criteria:  size of each character,endianness, and Byte Order Mark.=head2 by sizeUCS-2 is a fixed-length encoding with each character taking 16 bits.It B<does not> support I<surrogate pairs>.  When a surrogate pairis encountered during decode(), its place is filled with \x{FFFD}if I<CHECK> is 0, or the routine croaks if I<CHECK> is 1.  When acharacter whose ord value is larger than 0xFFFF is encountered,its place is filled with \x{FFFD} if I<CHECK> is 0, or the routinecroaks if I<CHECK> is 1.UTF-16 is almost the same as UCS-2 but it supports I<surrogate pairs>.When it encounters a high surrogate (0xD800-0xDBFF), it fetches thefollowing low surrogate (0xDC00-0xDFFF) and C<desurrogate>s them toform a character.  Bogus surrogates result in death.  When \x{10000}or above is encountered during encode(), it C<ensurrogate>s them andpushes the surrogate pair to the output stream.UTF-32 (UCS-4) is a fixed-length encoding with each character taking 32 bits.Since it is 32-bit, there is no need for I<surrogate pairs>.=head2 by endiannessThe first (and now failed) goal of Unicode was to map all characterrepertoires into a fixed-length integer so that programmers are happy.Since each character is either a I<short> or I<long> in C, you have topay attention to the endianness of each platform when you pass datato one another.Anything marked as BE is Big Endian (or network byte order) and LE isLittle Endian (aka VAX byte order).  For anything not marked eitherBE or LE, a character called Byte Order Mark (BOM) indicating theendianness is prepended to the string.CAVEAT: Though BOM in utf8 (\xEF\xBB\xBF) is valid, it is meaninglessand as of this writing Encode suite just leave it as is (\x{FeFF}).=over 4=item BOM as integer when fetched in network byte order              16         32 bits/char  -------------------------  BE      0xFeFF 0x0000FeFF  LE      0xFFFe 0xFFFe0000  -------------------------=backThis modules handles the BOM as follows.=over 4=item *When BE or LE is explicitly stated as the name of encoding, BOM issimply treated as a normal character (ZERO WIDTH NO-BREAK SPACE).=item *When BE or LE is omitted during decode(), it checks if BOM is at thebeginning of the string; if one is found, the endianness is set towhat the BOM says.  If no BOM is found, the routine dies.=item *When BE or LE is omitted during encode(), it returns a BE-encodedstring with BOM prepended.  So when you want to encode a whole textfile, make sure you encode() the whole text at once, not line by lineor each line, not file, will have a BOM prepended.=item *C<UCS-2> is an exception.  Unlike others, this is an alias of UCS-2BE.UCS-2 is already registered by IANA and others that way.=back=head1 Surrogate PairsTo say the least, surrogate pairs were the biggest mistake of theUnicode Consortium.  But according to the late Douglas Adams in I<TheHitchhiker's Guide to the Galaxy> Trilogy, C<In the beginning theUniverse was created. This has made a lot of people very angry andbeen widely regarded as a bad move>.  Their mistake was not of thismagnitude so let's forgive them.(I don't dare make any comparison with Unicode Consortium and theVogons here ;)  Or, comparing Encode to Babel Fish is completelyappropriate -- if you can only stick this into your ear :)Surrogate pairs were born when the Unicode Consortium finallyadmitted that 16 bits were not big enough to hold all the world'scharacter repertoires.  But they already made UCS-2 16-bit.  Whatdo we do?Back then, the range 0xD800-0xDFFF was not allocated.  Let's splitthat range in half and use the first half to represent the C<upperhalf of a character> and the second half to represent the C<lowerhalf of a character>.  That way, you can represent 1024 * 1024 =1048576 more characters.  Now we can store character ranges up to\x{10ffff} even with 16-bit encodings.  This pair of half-character isnow called a I<surrogate pair> and UTF-16 is the name of the encodingthat embraces them.Here is a formula to ensurrogate a Unicode character \x{10000} andabove;  $hi = ($uni - 0x10000) / 0x400 + 0xD800;  $lo = ($uni - 0x10000) % 0x400 + 0xDC00;And to desurrogate; $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);Note this move has made \x{D800}-\x{DFFF} into a forbidden zone butperl does not prohibit the use of characters within this range.  To perl, every one of \x{0000_0000} up to \x{ffff_ffff} (*) is I<a character>.  (*) or \x{ffff_ffff_ffff_ffff} if your perl is compiled with 64-bit  integer support!=head1 Error CheckingUnlike most encodings which accept various ways to handle errors,Unicode encodings simply croaks.  % perl -MEncode -e '$_ = "\xfe\xff\xd8\xd9\xda\xdb\0\n"' \         -e 'Encode::from_to($_, "utf16","shift_jis", 0); print'  UTF-16:Malformed LO surrogate d8d9 at /path/to/Encode.pm line 184.  % perl -MEncode -e '$a = "BOM missing"' \         -e ' Encode::from_to($a, "utf16", "shift_jis", 0); print'  UTF-16:Unrecognised BOM 424f at /path/to/Encode.pm line 184.Unlike other encodings where mappings are not one-to-one againstUnicode, UTFs are supposed to map 100% against one another.  So Encodeis more strict on UTFs.Consider that "division by zero" of Encode :)=head1 SEE ALSOL<Encode>, L<Encode::Unicode::UTF7>, L<http://www.unicode.org/glossary/>,L<http://www.unicode.org/unicode/faq/utf_bom.html>,RFC 2781 L<http://rfc.net/rfc2781.html>,The whole Unicode standard L<http://www.unicode.org/unicode/uni2book/u2.html>Ch. 15, pp. 403 of C<Programming Perl (3rd Edition)>by Larry Wall, Tom Christiansen, Jon Orwant; O'Reilly & Associates; ISBN 0-596-00027-8=cut