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+package Encode::Unicode;
+
+use strict;
+use warnings;
+no warnings 'redefine';
+
+our $VERSION = do { my @r = (q$Revision: 2.2 $ =~ /\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 NAME
+
+Encode::Unicode -- Various Unicode Transformation Formats
+
+=cut
+
+=head1 SYNOPSIS
+
+ use Encode qw/encode decode/;
+ $ucs2 = encode("UCS-2BE", $utf8);
+ $utf8 = decode("UCS-2BE", $ucs2);
+
+=head1 ABSTRACT
+
+This module implements all Character Encoding Schemes of Unicode that
+are 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 byte
+serialization. There are Seven character encoding schemes in Unicode:
+UTF-8, UTF-16, UTF-16BE, UTF-16LE, UTF-32 (UCS-4), UTF-32BE (UCS-4BE) and
+UTF-32LE (UCS-4LE), and UTF-7.
+
+Since UTF-7 is a 7-bit (re)encoded version of UTF-16BE, It is not part of
+Unicode's Character Encoding Scheme. It is separately implemented in
+Encode::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 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 BOM
+
+You can categorize these CES by 3 criteria: size of each character,
+endianness, and Byte Order Mark.
+
+=head2 by size
+
+UCS-2 is a fixed-length encoding with each character taking 16 bits.
+It B<does not> support I<surrogate pairs>. When a surrogate pair
+is 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 a
+character whose ord value is larger than 0xFFFF is encountered,
+its place is filled with \x{FFFD} if I<CHECK> is 0, or the routine
+croaks 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 the
+following low surrogate (0xDC00-0xDFFF) and C<desurrogate>s them to
+form a character. Bogus surrogates result in death. When \x{10000}
+or above is encountered during encode(), it C<ensurrogate>s them and
+pushes 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 endianness
+
+The first (and now failed) goal of Unicode was to map all character
+repertoires 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 to
+pay attention to the endianness of each platform when you pass data
+to one another.
+
+Anything marked as BE is Big Endian (or network byte order) and LE is
+Little Endian (aka VAX byte order). For anything not marked either
+BE or LE, a character called Byte Order Mark (BOM) indicating the
+endianness is prepended to the string.
+
+CAVEAT: Though BOM in utf8 (\xEF\xBB\xBF) is valid, it is meaningless
+and 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 0xFFeF 0xFFFe0000
+ -------------------------
+
+=back
+
+This modules handles the BOM as follows.
+
+=over 4
+
+=item *
+
+When BE or LE is explicitly stated as the name of encoding, BOM is
+simply 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 the
+beginning of the string; if one is found, the endianness is set to
+what the BOM says. If no BOM is found, the routine dies.
+
+=item *
+
+When BE or LE is omitted during encode(), it returns a BE-encoded
+string with BOM prepended. So when you want to encode a whole text
+file, make sure you encode() the whole text at once, not line by line
+or 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 Pairs
+
+To say the least, surrogate pairs were the biggest mistake of the
+Unicode Consortium. But according to the late Douglas Adams in I<The
+Hitchhiker's Guide to the Galaxy> Trilogy, C<In the beginning the
+Universe was created. This has made a lot of people very angry and
+been widely regarded as a bad move>. Their mistake was not of this
+magnitude so let's forgive them.
+
+(I don't dare make any comparison with Unicode Consortium and the
+Vogons here ;) Or, comparing Encode to Babel Fish is completely
+appropriate -- if you can only stick this into your ear :)
+
+Surrogate pairs were born when the Unicode Consortium finally
+admitted that 16 bits were not big enough to hold all the world's
+character repertoires. But they already made UCS-2 16-bit. What
+do we do?
+
+Back then, the range 0xD800-0xDFFF was not allocated. Let's split
+that range in half and use the first half to represent the C<upper
+half of a character> and the second half to represent the C<lower
+half 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 is
+now called a I<surrogate pair> and UTF-16 is the name of the encoding
+that embraces them.
+
+Here is a formula to ensurrogate a Unicode character \x{10000} and
+above;
+
+ $hi = ($uni - 0x10000) / 0x400 + 0xD800;
+ $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
+
+And to desurrogate;
+
+ $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
+
+Note this move has made \x{D800}-\x{DFFF} into a forbidden zone but
+perl does not prohibit the use of characters within this range. To perl,
+every one of \x{0000_0000} up to \x{ffff_ffff} (*) is I<a character>.
+
+ (*) or \x{ffff_ffff_ffff_ffff} if your perl is compiled with 64-bit
+ integer support!
+
+=head1 Error Checking
+
+Unlike most encodings which accept various ways to handle errors,
+Unicode encodings simply croaks.
+
+ % perl -MEncode -e '$_ = "\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 against
+Unicode, UTFs are supposed to map 100% against one another. So Encode
+is more strict on UTFs.
+
+Consider that "division by zero" of Encode :)
+
+=head1 SEE ALSO
+
+L<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