[p5sagit/p5-mst-13.2.git] / ext / Encode / Unicode / Unicode.pm

package Encode::Unicode;

use strict;
use warnings;

our $VERSION = do { my @r = (q$Revision: 1.36 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r };

use XSLoader;
XSLoader::load(__PACKAGE__,$VERSION);

#
# Object Generator 8 transcoders all at once!
#

require Encode;

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);

#
# three implementations of (en|de)code exist.  The XS version is the
# fastest.  *_modern uses an array and *_classic sticks with substr.
# *_classic is  much slower but more memory conservative.
# *_xs is the default.

sub set_transcoder{
    no warnings qw(redefine);
    my $type = shift;
    if    ($type eq "xs"){
	*decode = \&decode_xs;
	*encode = \&encode_xs;
    }elsif($type eq "modern"){
	*decode = \&decode_modern;
	*encode = \&encode_modern;
    }elsif($type eq "classic"){
	*decode = \&decode_classic;
	*encode = \&encode_classic;
    }else{
	require Carp; 
	Carp::croak __PACKAGE__, "::set_transcoder(modern|classic|xs)";
    }
}

set_transcoder("xs");

#
# Aux. subs & constants
#

sub FBCHAR(){ 0xFFFd }
sub BOM_BE(){ 0xFeFF }
sub BOM16LE(){ 0xFFFe }
sub BOM32LE(){ 0xFFFe0000 }

sub valid_ucs2($){
    return 
	(0 <= $_[0] && $_[0] < 0xD800) 
	    || 	( 0xDFFF < $_[0] && $_[0] <= 0xFFFF);
}

sub issurrogate($){   0xD800 <= $_[0]  && $_[0] <= 0xDFFF }
sub isHiSurrogate($){ 0xD800 <= $_[0]  && $_[0] <  0xDC00 }
sub isLoSurrogate($){ 0xDC00 <= $_[0]  && $_[0] <= 0xDFFF }

sub ensurrogate($){
    use integer; # we have divisions
    my $uni = shift;
    my  $hi = ($uni - 0x10000) / 0x400 + 0xD800;
    my  $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
    return ($hi, $lo);
}

sub desurrogate($$){
    my ($hi, $lo) = @_;
    return 0x10000 + ($hi - 0xD800)*0x400 + ($lo - 0xDC00);
}

sub Mask { {2 => 0xffff,  4 => 0xffffffff} }

#
# *_modern are much faster but guzzle more memory
#

sub decode_modern($$;$)
{
    my ($obj, $str, $chk ) = @_;
    my ($size, $endian, $ucs2) = @$obj{qw(size endian ucs2)};

    # warn "$size, $endian, $ucs2";
    $endian ||= BOMB($size, substr($str, 0, $size, ''))
	or poisoned2death($obj, "Where's the BOM?");
    my  $mask = Mask->{$size};
    my $utf8   = '';
    my @ord = unpack("$endian*", $str);
    undef $str; # to conserve memory
    while (@ord){
	my $ord = shift @ord;
	unless ($size == 4 or valid_ucs2($ord &= $mask)){
	    if ($ucs2){
		$chk and 
		    poisoned2death($obj, "no surrogates allowed", $ord);
		shift @ord; # skip the next one as well
		$ord = FBCHAR;
	    }else{
		unless (isHiSurrogate($ord)){
		    poisoned2death($obj, "Malformed HI surrogate", $ord);
		}
		my $lo = shift @ord;
		unless (isLoSurrogate($lo &= $mask)){
		    poisoned2death($obj, "Malformed LO surrogate", $ord, $lo);
		}
		$ord = desurrogate($ord, $lo);
	    }
	}
	$utf8 .= chr($ord);
    }
    utf8::upgrade($utf8);
    return $utf8;
}

sub encode_modern($$;$)
{
    my ($obj, $utf8, $chk) = @_;
    my ($size, $endian, $ucs2) = @$obj{qw(size endian ucs2)};
    my @str = ();
    unless ($endian){
	$endian = ($size == 4) ? 'N' : 'n';
	push @str, BOM_BE;
    }
    my @ord = unpack("U*", $utf8);
    undef $utf8; # to conserve memory
    for my $ord (@ord){
	unless ($size == 4 or valid_ucs2($ord)) {
	    unless(issurrogate($ord)){
		if ($ucs2){
		    $chk and 
			poisoned2death($obj, "code point too high", $ord);

		    push @str, FBCHAR;
		}else{
		 
		    push @str, ensurrogate($ord);
		}
	    }else{  # not supposed to happen
		push @str, FBCHAR;
	    }
	}else{
	    push @str, $ord;
	}
    }
    return pack("$endian*", @str);
}

#
# *_classic are slower but more memory conservative
#

sub decode_classic($$;$)
{
    my ($obj, $str, $chk ) = @_;
    my ($size, $endian, $ucs2) = @$obj{qw(size endian ucs2)};

    # warn "$size, $endian, $ucs2";
    $endian ||= BOMB($size, substr($str, 0, $size, ''))
	or poisoned2death($obj, "Where's the BOM?");
    my  $mask = Mask->{$size};
    my $utf8   = '';
    my @ord = unpack("$endian*", $str);
    while (length($str)){
	 my $ord = unpack($endian, substr($str, 0, $size, ''));
	unless ($size == 4 or valid_ucs2($ord &= $mask)){
	    if ($ucs2){
		$chk and 
		    poisoned2death($obj, "no surrogates allowed", $ord);
		substr($str,0,$size,''); # skip the next one as well
		$ord = FBCHAR;
	    }else{
		unless (isHiSurrogate($ord)){
		    poisoned2death($obj, "Malformed HI surrogate", $ord);
		}
		my $lo = unpack($endian ,substr($str,0,$size,''));
		unless (isLoSurrogate($lo &= $mask)){
		    poisoned2death($obj, "Malformed LO surrogate", $ord, $lo);
		}
		$ord = desurrogate($ord, $lo);
	    }
	}
	$utf8 .= chr($ord);
    }
    utf8::upgrade($utf8);
    return $utf8;
}

sub encode_classic($$;$)
{
    my ($obj, $utf8, $chk) = @_;
    my ($size, $endian, $ucs2) = @$obj{qw(size endian ucs2)};
    # warn join ", ", $size, $ucs2, $endian, $mask;
    my $str   = '';
    unless ($endian){
	$endian = ($size == 4) ? 'N' : 'n';
	$str .= pack($endian, BOM_BE);
    }
    while (length($utf8)){
	my $ord  = ord(substr($utf8,0,1,''));
	unless ($size == 4 or valid_ucs2($ord)) {
	    unless(issurrogate($ord)){
		if ($ucs2){
		    $chk and 
			poisoned2death($obj, "code point too high", $ord);
		    $str .= pack($endian, FBCHAR);
		}else{
		    $str .= pack($endian.2, ensurrogate($ord));
		}
	    }else{  # not supposed to happen
		$str .= pack($endian, FBCHAR);
	    }
	}else{
	    $str .= pack($endian, $ord);
	}
    }
    return $str;
}

sub BOMB {
    my ($size, $bom) = @_;
    my $N = $size == 2 ? 'n' : 'N';
    my $ord = unpack($N, $bom);
    return ($ord eq BOM_BE) ? $N : 
	($ord eq BOM16LE) ? 'v' : ($ord eq BOM32LE) ? 'V' : undef;
}

sub poisoned2death{
    my $obj = shift;
    my $msg = shift;
    my $pair = join(", ", map {sprintf "\\x%x", $_} @_);
    require Carp;
    Carp::croak $obj->name, ":", $msg, "<$pair>.", caller;
}

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, UTF-32BE and UTF-32LE.

=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 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.

=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 SEE ALSO

L<Encode>, L<http://www.unicode.org/glossary/>,

RFC 2781 L<http://rfc.net/rfc2781.html>,

L<http://www.unicode.org/unicode/faq/utf_bom.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
Commit	Line	Data
f2a2953c	1	package Encode::Unicode;
f2a2953c	2
df1df145	3	use strict;
f2a2953c	4	use warnings;
f2a2953c	5
10c5ecbb	6	our $VERSION = do { my @r = (q$Revision: 1.36 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r };
f2a2953c	7
85982a32	8	use XSLoader;
85982a32	9	XSLoader::load(__PACKAGE__,$VERSION);
df1df145	10
f2a2953c	11	#
	12	# Object Generator 8 transcoders all at once!
	13	#
df1df145	14
f2a2953c	15	require Encode;
10c5ecbb	16
f2a2953c	17	for my $name (qw(UTF-16 UTF-16BE UTF-16LE
	18	UTF-32 UTF-32BE UTF-32LE
	19	UCS-2BE UCS-2LE))
df1df145	20	{
f2a2953c	21	my ($size, $endian, $ucs2, $mask);
	22	$name =~ /^(\w+)-(\d+)(\w*)$/o;
	23	if ($ucs2 = ($1 eq 'UCS')){
	24	$size = 2;
	25	}else{
	26	$size = $2/8;
df1df145	27	}
f2a2953c	28	$endian = ($3 eq 'BE') ? 'n' : ($3 eq 'LE') ? 'v' : '' ;
	29	$size == 4 and $endian = uc($endian);
	30
	31	$Encode::Encoding{$name} =
	32	bless {
	33	Name => $name,
	34	size => $size,
	35	endian => $endian,
	36	ucs2 => $ucs2,
c731e18e	37	} => __PACKAGE__;
f2a2953c	38
df1df145	39	}
df1df145	40
10c5ecbb	41	use base qw(Encode::Encoding);
f2a2953c	42
f2a2953c	43	#
0ab8f81e	44	# three implementations of (en\|de)code exist. The XS version is the
	45	# fastest. _modern uses an array and _classic sticks with substr.
	46	# *_classic is much slower but more memory conservative.
	47	# *_xs is the default.
f2a2953c	48
	49	sub set_transcoder{
	50	no warnings qw(redefine);
	51	my $type = shift;
aae85ceb	52	if ($type eq "xs"){
	53	*decode = \&decode_xs;
	54	*encode = \&encode_xs;
	55	}elsif($type eq "modern"){
f2a2953c	56	*decode = \&decode_modern;
	57	*encode = \&encode_modern;
	58	}elsif($type eq "classic"){
	59	*decode = \&decode_classic;
	60	*encode = \&encode_classic;
	61	}else{
fcb875d4	62	require Carp;
aae85ceb	63	Carp::croak __PACKAGE__, "::set_transcoder(modern\|classic\|xs)";
f2a2953c	64	}
	65	}
	66
aae85ceb	67	set_transcoder("xs");
f2a2953c	68
f2a2953c	69	#
85982a32	70	# Aux. subs & constants
	71	#
	72
	73	sub FBCHAR(){ 0xFFFd }
	74	sub BOM_BE(){ 0xFeFF }
	75	sub BOM16LE(){ 0xFFFe }
	76	sub BOM32LE(){ 0xFFFe0000 }
	77
	78	sub valid_ucs2($){
	79	return
	80	(0 <= $_[0] && $_[0] < 0xD800)
	81	\|\| ( 0xDFFF < $_[0] && $_[0] <= 0xFFFF);
	82	}
	83
	84	sub issurrogate($){ 0xD800 <= $_[0] && $_[0] <= 0xDFFF }
	85	sub isHiSurrogate($){ 0xD800 <= $_[0] && $_[0] < 0xDC00 }
	86	sub isLoSurrogate($){ 0xDC00 <= $_[0] && $_[0] <= 0xDFFF }
	87
	88	sub ensurrogate($){
	89	use integer; # we have divisions
	90	my $uni = shift;
	91	my $hi = ($uni - 0x10000) / 0x400 + 0xD800;
	92	my $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
	93	return ($hi, $lo);
	94	}
	95
	96	sub desurrogate($$){
	97	my ($hi, $lo) = @_;
	98	return 0x10000 + ($hi - 0xD800)*0x400 + ($lo - 0xDC00);
	99	}
	100
	101	sub Mask { {2 => 0xffff, 4 => 0xffffffff} }
	102
	103	#
f2a2953c	104	# *_modern are much faster but guzzle more memory
	105	#
	106
aae85ceb	107	sub decode_modern($$;$)
df1df145	108	{
f2a2953c	109	my ($obj, $str, $chk ) = @_;
	110	my ($size, $endian, $ucs2) = @$obj{qw(size endian ucs2)};
	111
	112	# warn "$size, $endian, $ucs2";
	113	$endian \|\|= BOMB($size, substr($str, 0, $size, ''))
	114	or poisoned2death($obj, "Where's the BOM?");
	115	my $mask = Mask->{$size};
	116	my $utf8 = '';
	117	my @ord = unpack("$endian*", $str);
	118	undef $str; # to conserve memory
	119	while (@ord){
	120	my $ord = shift @ord;
	121	unless ($size == 4 or valid_ucs2($ord &= $mask)){
	122	if ($ucs2){
fcb875d4	123	$chk and
f2a2953c	124	poisoned2death($obj, "no surrogates allowed", $ord);
	125	shift @ord; # skip the next one as well
	126	$ord = FBCHAR;
	127	}else{
	128	unless (isHiSurrogate($ord)){
	129	poisoned2death($obj, "Malformed HI surrogate", $ord);
	130	}
	131	my $lo = shift @ord;
	132	unless (isLoSurrogate($lo &= $mask)){
	133	poisoned2death($obj, "Malformed LO surrogate", $ord, $lo);
	134	}
	135	$ord = desurrogate($ord, $lo);
	136	}
	137	}
	138	$utf8 .= chr($ord);
df1df145	139	}
f2a2953c	140	utf8::upgrade($utf8);
	141	return $utf8;
	142	}
	143
aae85ceb	144	sub encode_modern($$;$)
f2a2953c	145	{
	146	my ($obj, $utf8, $chk) = @_;
	147	my ($size, $endian, $ucs2) = @$obj{qw(size endian ucs2)};
	148	my @str = ();
	149	unless ($endian){
	150	$endian = ($size == 4) ? 'N' : 'n';
	151	push @str, BOM_BE;
	152	}
	153	my @ord = unpack("U*", $utf8);
	154	undef $utf8; # to conserve memory
	155	for my $ord (@ord){
	156	unless ($size == 4 or valid_ucs2($ord)) {
	157	unless(issurrogate($ord)){
	158	if ($ucs2){
fcb875d4	159	$chk and
f2a2953c	160	poisoned2death($obj, "code point too high", $ord);
	161
	162	push @str, FBCHAR;
	163	}else{
fcb875d4	164
f2a2953c	165	push @str, ensurrogate($ord);
	166	}
	167	}else{ # not supposed to happen
	168	push @str, FBCHAR;
	169	}
	170	}else{
	171	push @str, $ord;
	172	}
	173	}
	174	return pack("$endian*", @str);
	175	}
	176
	177	#
	178	# *_classic are slower but more memory conservative
	179	#
	180
aae85ceb	181	sub decode_classic($$;$)
f2a2953c	182	{
	183	my ($obj, $str, $chk ) = @_;
	184	my ($size, $endian, $ucs2) = @$obj{qw(size endian ucs2)};
	185
	186	# warn "$size, $endian, $ucs2";
	187	$endian \|\|= BOMB($size, substr($str, 0, $size, ''))
	188	or poisoned2death($obj, "Where's the BOM?");
	189	my $mask = Mask->{$size};
	190	my $utf8 = '';
	191	my @ord = unpack("$endian*", $str);
	192	while (length($str)){
	193	my $ord = unpack($endian, substr($str, 0, $size, ''));
	194	unless ($size == 4 or valid_ucs2($ord &= $mask)){
	195	if ($ucs2){
fcb875d4	196	$chk and
f2a2953c	197	poisoned2death($obj, "no surrogates allowed", $ord);
	198	substr($str,0,$size,''); # skip the next one as well
	199	$ord = FBCHAR;
	200	}else{
	201	unless (isHiSurrogate($ord)){
	202	poisoned2death($obj, "Malformed HI surrogate", $ord);
	203	}
	204	my $lo = unpack($endian ,substr($str,0,$size,''));
	205	unless (isLoSurrogate($lo &= $mask)){
	206	poisoned2death($obj, "Malformed LO surrogate", $ord, $lo);
	207	}
	208	$ord = desurrogate($ord, $lo);
	209	}
	210	}
	211	$utf8 .= chr($ord);
	212	}
	213	utf8::upgrade($utf8);
	214	return $utf8;
	215	}
	216
aae85ceb	217	sub encode_classic($$;$)
f2a2953c	218	{
	219	my ($obj, $utf8, $chk) = @_;
	220	my ($size, $endian, $ucs2) = @$obj{qw(size endian ucs2)};
	221	# warn join ", ", $size, $ucs2, $endian, $mask;
	222	my $str = '';
	223	unless ($endian){
	224	$endian = ($size == 4) ? 'N' : 'n';
	225	$str .= pack($endian, BOM_BE);
	226	}
	227	while (length($utf8)){
	228	my $ord = ord(substr($utf8,0,1,''));
	229	unless ($size == 4 or valid_ucs2($ord)) {
	230	unless(issurrogate($ord)){
	231	if ($ucs2){
fcb875d4	232	$chk and
f2a2953c	233	poisoned2death($obj, "code point too high", $ord);
	234	$str .= pack($endian, FBCHAR);
	235	}else{
	236	$str .= pack($endian.2, ensurrogate($ord));
	237	}
	238	}else{ # not supposed to happen
	239	$str .= pack($endian, FBCHAR);
	240	}
	241	}else{
	242	$str .= pack($endian, $ord);
	243	}
	244	}
	245	return $str;
	246	}
	247
	248	sub BOMB {
	249	my ($size, $bom) = @_;
	250	my $N = $size == 2 ? 'n' : 'N';
	251	my $ord = unpack($N, $bom);
fcb875d4	252	return ($ord eq BOM_BE) ? $N :
f2a2953c	253	($ord eq BOM16LE) ? 'v' : ($ord eq BOM32LE) ? 'V' : undef;
	254	}
	255
	256	sub poisoned2death{
	257	my $obj = shift;
	258	my $msg = shift;
	259	my $pair = join(", ", map {sprintf "\\x%x", $_} @_);
	260	require Carp;
	261	Carp::croak $obj->name, ":", $msg, "<$pair>.", caller;
df1df145	262	}
	263
	264	1;
	265	__END__
67d7b5ef	266
	267	=head1 NAME
	268
0ab8f81e	269	Encode::Unicode -- Various Unicode Transformation Formats
67d7b5ef	270
67d7b5ef	271	=cut
f2a2953c	272
	273	=head1 SYNOPSIS
	274
fcb875d4	275	use Encode qw/encode decode/;
f2a2953c	276	$ucs2 = encode("UCS-2BE", $utf8);
	277	$utf8 = decode("UCS-2BE", $ucs2);
	278
	279	=head1 ABSTRACT
	280
	281	This module implements all Character Encoding Schemes of Unicode that
	282	are officially documented by Unicode Consortium (except, of course,
	283	for UTF-8, which is a native format in perl).
	284
	285	=over 4
	286
	287	=item L<http://www.unicode.org/glossary/> says:
	288
	289	I<Character Encoding Scheme> A character encoding form plus byte
	290	serialization. There are seven character encoding schemes in Unicode:
	291	UTF-8, UTF-16, UTF-16BE, UTF-16LE, UTF-32, UTF-32BE and UTF-32LE.
	292
	293	=item Quick Reference
	294
	295	Decodes from ord(N) Encodes chr(N) to...
	296	octet/char BOM S.P d800-dfff ord > 0xffff \x{1abcd} ==
	297	---------------+-----------------+------------------------------
	298	UCS-2BE 2 N N is bogus Not Available
	299	UCS-2LE 2 N N bogus Not Available
	300	UTF-16 2/4 Y Y is S.P S.P BE/LE
	301	UTF-16BE 2/4 N Y S.P S.P 0xd82a,0xdfcd
	302	UTF-16LE 2 N Y S.P S.P 0x2ad8,0xcddf
	303	UTF-32 4 Y - is bogus As is BE/LE
0ab8f81e	304	UTF-32BE 4 N - bogus As is 0x0001abcd
0ab8f81e	305	UTF-32LE 4 N - bogus As is 0xcdab0100
f2a2953c	306	UTF-8 1-4 - - bogus >= 4 octets \xf0\x9a\af\8d
	307	---------------+-----------------+------------------------------
	308
	309	=back
	310
	311	=head1 Size, Endianness, and BOM
	312
0ab8f81e	313	You can categorize these CES by 3 criteria: size of each character,
0ab8f81e	314	endianness, and Byte Order Mark.
f2a2953c	315
0ab8f81e	316	=head2 by size
f2a2953c	317
f2a2953c	318	UCS-2 is a fixed-length encoding with each character taking 16 bits.
0ab8f81e	319	It B<does not> support I<surrogate pairs>. When a surrogate pair
	320	is encountered during decode(), its place is filled with \x{FFFD}
	321	if I<CHECK> is 0, or the routine croaks if I<CHECK> is 1. When a
	322	character whose ord value is larger than 0xFFFF is encountered,
	323	its place is filled with \x{FFFD} if I<CHECK> is 0, or the routine
	324	croaks if I<CHECK> is 1.
	325
	326	UTF-16 is almost the same as UCS-2 but it supports I<surrogate pairs>.
f2a2953c	327	When it encounters a high surrogate (0xD800-0xDBFF), it fetches the
0ab8f81e	328	following low surrogate (0xDC00-0xDFFF) and C<desurrogate>s them to
	329	form a character. Bogus surrogates result in death. When \x{10000}
	330	or above is encountered during encode(), it C<ensurrogate>s them and
	331	pushes the surrogate pair to the output stream.
f2a2953c	332
f2a2953c	333	UTF-32 is a fixed-length encoding with each character taking 32 bits.
0ab8f81e	334	Since it is 32-bit, there is no need for I<surrogate pairs>.
f2a2953c	335
0ab8f81e	336	=head2 by endianness
f2a2953c	337
0ab8f81e	338	The first (and now failed) goal of Unicode was to map all character
	339	repertoires into a fixed-length integer so that programmers are happy.
	340	Since each character is either a I<short> or I<long> in C, you have to
	341	pay attention to the endianness of each platform when you pass data
	342	to one another.
f2a2953c	343
f2a2953c	344	Anything marked as BE is Big Endian (or network byte order) and LE is
0ab8f81e	345	Little Endian (aka VAX byte order). For anything not marked either
	346	BE or LE, a character called Byte Order Mark (BOM) indicating the
	347	endianness is prepended to the string.
f2a2953c	348
	349	=over 4
	350
fcb875d4	351	=item BOM as integer when fetched in network byte order
f2a2953c	352
fcb875d4	353	16 32 bits/char
	354	-------------------------
	355	BE 0xFeFF 0x0000FeFF
	356	LE 0xFFeF 0xFFFe0000
	357	-------------------------
f2a2953c	358
f2a2953c	359	=back
fcb875d4	360
0ab8f81e	361	This modules handles the BOM as follows.
f2a2953c	362
	363	=over 4
	364
	365	=item *
	366
	367	When BE or LE is explicitly stated as the name of encoding, BOM is
0ab8f81e	368	simply treated as a normal character (ZERO WIDTH NO-BREAK SPACE).
f2a2953c	369
	370	=item *
	371
0ab8f81e	372	When BE or LE is omitted during decode(), it checks if BOM is at the
	373	beginning of the string; if one is found, the endianness is set to
	374	what the BOM says. If no BOM is found, the routine dies.
f2a2953c	375
	376	=item *
	377
	378	When BE or LE is omitted during encode(), it returns a BE-encoded
	379	string with BOM prepended. So when you want to encode a whole text
0ab8f81e	380	file, make sure you encode() the whole text at once, not line by line
0ab8f81e	381	or each line, not file, will have a BOM prepended.
f2a2953c	382
	383	=item *
	384
0ab8f81e	385	C<UCS-2> is an exception. Unlike others, this is an alias of UCS-2BE.
f2a2953c	386	UCS-2 is already registered by IANA and others that way.
f2a2953c	387
fdd579e2	388	=back
f2a2953c	389
fcb875d4	390	=head1 Surrogate Pairs
f2a2953c	391
fcb875d4	392	To say the least, surrogate pairs were the biggest mistake of the
	393	Unicode Consortium. But according to the late Douglas Adams in I<The
	394	Hitchhiker's Guide to the Galaxy> Trilogy, C<In the beginning the
	395	Universe was created. This has made a lot of people very angry and
	396	been widely regarded as a bad move>. Their mistake was not of this
	397	magnitude so let's forgive them.
f2a2953c	398
f2a2953c	399	(I don't dare make any comparison with Unicode Consortium and the
c731e18e	400	Vogons here ;) Or, comparing Encode to Babel Fish is completely
c731e18e	401	appropriate -- if you can only stick this into your ear :)
f2a2953c	402
0ab8f81e	403	Surrogate pairs were born when the Unicode Consortium finally
fcb875d4	404	admitted that 16 bits were not big enough to hold all the world's
0ab8f81e	405	character repertoires. But they already made UCS-2 16-bit. What
f2a2953c	406	do we do?
f2a2953c	407
0ab8f81e	408	Back then, the range 0xD800-0xDFFF was not allocated. Let's split
	409	that range in half and use the first half to represent the C<upper
	410	half of a character> and the second half to represent the C<lower
	411	half of a character>. That way, you can represent 1024 * 1024 =
	412	1048576 more characters. Now we can store character ranges up to
	413	\x{10ffff} even with 16-bit encodings. This pair of half-character is
	414	now called a I<surrogate pair> and UTF-16 is the name of the encoding
	415	that embraces them.
f2a2953c	416
448e90bb	417	Here is a formula to ensurrogate a Unicode character \x{10000} and
f2a2953c	418	above;
	419
	420	$hi = ($uni - 0x10000) / 0x400 + 0xD800;
	421	$lo = ($uni - 0x10000) % 0x400 + 0xDC00;
	422
	423	And to desurrogate;
	424
	425	$uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00);
	426
fcb875d4	427	Note this move has made \x{D800}-\x{DFFF} into a forbidden zone but
	428	perl does not prohibit the use of characters within this range. To perl,
	429	every one of \x{0000_0000} up to \x{ffff_ffff} (*) is I<a character>.
	430
	431	(*) or \x{ffff_ffff_ffff_ffff} if your perl is compiled with 64-bit
0ab8f81e	432	integer support!
f2a2953c	433
	434	=head1 SEE ALSO
	435
fdd579e2	436	L<Encode>, L<http://www.unicode.org/glossary/>,
f2a2953c	437
fdd579e2	438	RFC 2781 L<http://rfc.net/rfc2781.html>,
	439
	440	L<http://www.unicode.org/unicode/faq/utf_bom.html>
	441
fcb875d4	442	Ch. 15, pp. 403 of C<Programming Perl (3rd Edition)>
	443	by Larry Wall, Tom Christiansen, Jon Orwant;
	444	O'Reilly & Associates; ISBN 0-596-00027-8
	445
fdd579e2	446	=cut