Encode API documentation nd tidy up.

Minor additions to test.
Tweaks sv_utf8_upgrade() to force SvPV, and always SvUTF8_on and return length.
Adds STRLEN to standard typemap.

p4raw-id: //depot/perlio@8923

2 files changed, 519 insertions, 418 deletions

diff --git a/ext/Encode/Encode.pm b/ext/Encode/Encode.pm
index 1f4ffb1485..769b8daf46 100644
--- a/ext/Encode/Encode.pm
+++ b/ext/Encode/Encode.pm
@@ -7,345 +7,37 @@ require Exporter;
 
 @ISA = qw(Exporter DynaLoader);
 
+# Public, encouraged API is exported by default
+@EXPORT = qw (
+  encode
+  decode
+  encode_utf8
+  decode_utf8
+  find_encoding
+);
+
 @EXPORT_OK =
     qw(
-       bytes_to_utf8
-       utf8_to_bytes
-       chars_to_utf8
-       utf8_to_chars
-       utf8_to_chars_check
-       bytes_to_chars
-       chars_to_bytes
+       encodings
        from_to
        is_utf8
-       on_utf8
-       off_utf8
-       utf_to_utf
-       encodings
-       utf8_decode
-       utf8_encode
+       is_8bit
+       is_16bit
        utf8_upgrade
        utf8_downgrade
+       _utf8_on
+       _utf8_off
       );
 
 bootstrap Encode ();
 
-=pod
-
-=head1 NAME
-
-Encode - character encodings
-
-=head2 TERMINOLOGY
-
-=over
-
-=item *
-
-I<char>: a character in the range 0..maxint (at least 2**32-1)
-
-=item *
-
-I<byte>: a character in the range 0..255
-
-=back
-
-The marker [INTERNAL] marks Internal Implementation Details, in
-general meant only for those who think they know what they are doing,
-and such details may change in future releases.
-
-=head2 bytes
-
-=over 4
-
-=item *
-
-        bytes_to_utf8(STRING [, FROM])
-
-The bytes in STRING are recoded in-place into UTF-8.  If no FROM is
-specified the bytes are expected to be encoded in US-ASCII or ISO
-8859-1 (Latin 1).  Returns the new size of STRING, or C<undef> if
-there's a failure.
-
-[INTERNAL] Also the UTF-8 flag of STRING is turned on.
-
-=item *
-
-        utf8_to_bytes(STRING [, TO [, CHECK]])
-
-The UTF-8 in STRING is decoded in-place into bytes.  If no TO encoding
-is specified the bytes are expected to be encoded in US-ASCII or ISO
-8859-1 (Latin 1).  Returns the new size of STRING, or C<undef> if
-there's a failure.
-
-What if there are characters > 255?  What if the UTF-8 in STRING is
-malformed?  See L</"Handling Malformed Data">.
-
-[INTERNAL] The UTF-8 flag of STRING is not checked.
-
-=back
-
-=head2 chars
-
-=over 4
-
-=item *
-
-        chars_to_utf8(STRING)
-
-The chars in STRING are encoded in-place into UTF-8.  Returns the new
-size of STRING, or C<undef> if there's a failure.
-
-No assumptions are made on the encoding of the chars.  If you want to
-assume that the chars are Unicode and to trap illegal Unicode
-characters, you must use C<from_to('Unicode', ...)>.
-
-[INTERNAL] Also the UTF-8 flag of STRING is turned on.
-
-=over 4
-
-=item *
-
-        utf8_to_chars(STRING)
-
-The UTF-8 in STRING is decoded in-place into chars.  Returns the new
-size of STRING, or C<undef> if there's a failure.
-
-If the UTF-8 in STRING is malformed C<undef> is returned, and also an
-optional lexical warning (category utf8) is given.
-
-[INTERNAL] The UTF-8 flag of STRING is not checked.
-
-=item *
-
-        utf8_to_chars_check(STRING [, CHECK])
-
-(Note that special naming of this interface since a two-argument
-utf8_to_chars() has different semantics.)
-
-The UTF-8 in STRING is decoded in-place into chars.  Returns the new
-size of STRING, or C<undef> if there is a failure.
-
-If the UTF-8 in STRING is malformed?  See L</"Handling Malformed Data">.
-
-[INTERNAL] The UTF-8 flag of STRING is not checked.
-
-=back
-
-=head2 chars With Encoding
-
-=over 4
-
-=item *
-
-        chars_to_utf8(STRING, FROM [, CHECK])
-
-The chars in STRING encoded in FROM are recoded in-place into UTF-8.
-Returns the new size of STRING, or C<undef> if there's a failure.
-
-No assumptions are made on the encoding of the chars.  If you want to
-assume that the chars are Unicode and to trap illegal Unicode
-characters, you must use C<from_to('Unicode', ...)>.
-
-[INTERNAL] Also the UTF-8 flag of STRING is turned on.
-
-=item *
-
-        utf8_to_chars(STRING, TO [, CHECK])
-
-The UTF-8 in STRING is decoded in-place into chars encoded in TO.
-Returns the new size of STRING, or C<undef> if there's a failure.
-
-If the UTF-8 in STRING is malformed?  See L</"Handling Malformed Data">.
-
-[INTERNAL] The UTF-8 flag of STRING is not checked.
-
-=item *
-
-	bytes_to_chars(STRING, FROM [, CHECK])
-
-The bytes in STRING encoded in FROM are recoded in-place into chars.
-Returns the new size of STRING in bytes, or C<undef> if there's a
-failure.
-
-If the mapping is impossible?  See L</"Handling Malformed Data">.
-
-=item *
-
-	chars_to_bytes(STRING, TO [, CHECK])
-
-The chars in STRING are recoded in-place to bytes encoded in TO.
-Returns the new size of STRING in bytes, or C<undef> if there's a
-failure.
-
-If the mapping is impossible?  See L</"Handling Malformed Data">.
-
-=item *
-
-        from_to(STRING, FROM, TO [, CHECK])
-
-The chars in STRING encoded in FROM are recoded in-place into TO.
-Returns the new size of STRING, or C<undef> if there's a failure.
-
-If mapping between the encodings is impossible?
-See L</"Handling Malformed Data">.
-
-[INTERNAL] If TO is UTF-8, also the UTF-8 flag of STRING is turned on.
-
-=back
-
-=head2 Testing For UTF-8
-
-=over 4
-
-=item *
-
-        is_utf8(STRING [, CHECK])
-
-[INTERNAL] Test whether the UTF-8 flag is turned on in the STRING.
-If CHECK is true, also checks the data in STRING for being
-well-formed UTF-8.  Returns true if successful, false otherwise.
-
-=back
-
-=head2 Toggling UTF-8-ness
-
-=over 4
-
-=item *
-
-        on_utf8(STRING)
-
-[INTERNAL] Turn on the UTF-8 flag in STRING.  The data in STRING is
-B<not> checked for being well-formed UTF-8.  Do not use unless you
-B<know> that the STRING is well-formed UTF-8.  Returns the previous
-state of the UTF-8 flag (so please don't test the return value as
-I<not> success or failure), or C<undef> if STRING is not a string.
-
-=item *
-
-        off_utf8(STRING)
-
-[INTERNAL] Turn off the UTF-8 flag in STRING.  Do not use frivolously.
-Returns the previous state of the UTF-8 flag (so please don't test the
-return value as I<not> success or failure), or C<undef> if STRING is
-not a string.
-
-=back
-
-=head2 UTF-16 and UTF-32 Encodings
-
-=over 4
-
-=item *
-
-        utf_to_utf(STRING, FROM, TO [, CHECK])
-
-The data in STRING is converted from Unicode Transfer Encoding FROM to
-Unicode Transfer Encoding TO.  Both FROM and TO may be any of the
-following tags (case-insensitive, with or without 'utf' or 'utf-' prefix):
-
-        tag             meaning
-
-        '7'             UTF-7
-        '8'             UTF-8
-        '16be'          UTF-16 big-endian
-        '16le'          UTF-16 little-endian
-        '16'            UTF-16 native-endian
-        '32be'          UTF-32 big-endian
-        '32le'          UTF-32 little-endian
-        '32'            UTF-32 native-endian
-
-UTF-16 is also known as UCS-2, 16 bit or 2-byte chunks, and UTF-32 as
-UCS-4, 32-bit or 4-byte chunks.  Returns the new size of STRING, or
-C<undef> is there's a failure.
-
-If FROM is UTF-8 and the UTF-8 in STRING is malformed?  See
-L</"Handling Malformed Data">.
-
-[INTERNAL] Even if CHECK is true and FROM is UTF-8, the UTF-8 flag of
-STRING is not checked.  If TO is UTF-8, also the UTF-8 flag of STRING is
-turned on.  Identical FROM and TO are fine.
-
-=back
-
-=head2 Handling Malformed Data
-
-If CHECK is not set, C<undef> is returned.  If the data is supposed to
-be UTF-8, an optional lexical warning (category utf8) is given.  If
-CHECK is true but not a code reference, dies.  If CHECK is a code
-reference, it is called with the arguments
-
-	(MALFORMED_STRING, STRING_FROM_SO_FAR, STRING_TO_SO_FAR)
-
-Two return values are expected from the call: the string to be used in
-the result string in place of the malformed section, and the length of
-the malformed section in bytes.
-
-=cut
-
-sub bytes_to_utf8 {
-    &_bytes_to_utf8;
-}
-
-sub utf8_to_bytes {
-    &_utf8_to_bytes;
-}
-
-sub chars_to_utf8 {
-    &C_to_utf8;
-}
-
-sub utf8_to_chars {
-    &_utf8_to_chars;
-}
-
-sub utf8_to_chars_check {
-    &_utf8_to_chars_check;
-}
-
-sub bytes_to_chars {
-    &_bytes_to_chars;
-}
-
-sub chars_to_bytes {
-    &_chars_to_bytes;
-}
-
-sub is_utf8 {
-    &_is_utf8;
-}
-
-sub on_utf8 {
-    &_on_utf8;
-}
-
-sub off_utf8 {
-    &_off_utf8;
-}
-
-sub utf_to_utf {
-    &_utf_to_utf;
-}
+# Documentation moved after __END__ for speed - NI-S
 
 use Carp;
 
-sub from_to
-{
- my ($string,$from,$to,$check) = @_;
- my $f = __PACKAGE__->getEncoding($from);
- croak("Unknown encoding '$from'") unless $f;
- my $t = __PACKAGE__->getEncoding($to);
- croak("Unknown encoding '$to'") unless $t;
- my $uni = $f->toUnicode($string,$check);
- return undef if ($check && length($string));
- $string = $t->fromUnicode($uni,$check);
- return undef if ($check && length($uni));
- return length($_[0] = $string);
-}
-
 # The global hash is declared in XS code
-$encoding{Unicode}    = bless({},'Encode::Unicode');
+$encoding{Unicode}      = bless({},'Encode::Unicode');
+$encoding{utf8}         = bless({},'Encode::utf8');
 $encoding{'iso10646-1'} = bless({},'Encode::iso10646_1');
 
 sub encodings
@@ -410,6 +102,60 @@ sub getEncoding
  return $enc;
 }
 
+sub find_encoding
+{
+ my ($name) = @_;
+ return __PACKAGE__->getEncoding($name);
+}
+
+sub encode
+{
+ my ($name,$string,$check) = @_;
+ my $enc = find_encoding($name);
+ croak("Unknown encoding '$name'") unless defined $enc;
+ my $octets = $enc->fromUnicode($string,$check);
+ return undef if ($check && length($string));
+ return $octets;
+}
+
+sub decode
+{
+ my ($name,$octets,$check) = @_;
+ my $enc = find_encoding($name);
+ croak("Unknown encoding '$name'") unless defined $enc;
+ my $string = $enc->toUnicode($octets,$check);
+ return undef if ($check && length($octets));
+ return $string;
+}
+
+sub from_to
+{
+ my ($string,$from,$to,$check) = @_;
+ my $f = find_encoding($from);
+ croak("Unknown encoding '$from'") unless defined $f;
+ my $t = find_encoding($to);
+ croak("Unknown encoding '$to'") unless defined $t;
+ my $uni = $f->toUnicode($string,$check);
+ return undef if ($check && length($string));
+ $string = $t->fromUnicode($uni,$check);
+ return undef if ($check && length($uni));
+ return length($_[0] = $string);
+}
+
+sub encode_utf8
+{
+ my ($str) = @_;
+ utf8_encode($str);
+ return $str;
+}
+
+sub decode_utf8
+{
+ my ($str) = @_;
+ return undef unless utf8_decode($str);
+ return $str;
+}
+
 package Encode::Unicode;
 
 # Dummy package that provides the encode interface but leaves data
@@ -427,6 +173,37 @@ sub toUnicode
 
 *fromUnicode = \&toUnicode;
 
+package Encode::utf8;
+
+# package to allow long-hand
+#   $octets = encode( utf8 => $string );
+#
+
+sub name { 'utf8' }
+
+sub toUnicode
+{
+ my ($obj,$octets,$chk) = @_;
+ my $str = decode_utf8($octets);
+ if (defined $str)
+  {
+   $_[1] = '' if $chk;
+   return $str;
+  }
+ return undef;
+}
+
+sub fromUnicode
+{
+ my ($obj,$string,$chk) = @_;
+ my $octets = encode_utf8($string);
+ $_[1] = '' if $chk;
+ return $octets;
+
+}
+
+*fromUnicode = \&toUnicode;
+
 package Encode::Table;
 
 sub read
@@ -613,6 +390,415 @@ sub fromUnicode
  croak("Not implemented yet");
 }
 
+# switch back to Encode package in case we ever add AutoLoader
+package Encode;
+
 1;
 
+=head1 NAME
+
+Encode - character encodings
+
+=head1 SYNOPSIS
+
+    use Encode;
+
+=head1 DESCRIPTION
+
+The C<Encode> module provides the interfaces between perl's strings
+and the rest of the system. Perl strings are sequences of B<characters>.
+
+The repertoire of characters that Perl can represent is at least that
+defined by the Unicode Consortium. On most platforms the ordinal values
+of the  characters (as returned by C<ord(ch)>) is the "Unicode codepoint" for
+the character (the exceptions are those platforms where the legacy
+encoding is some variant of EBCDIC rather than a super-set of ASCII
+- see L<perlebcdic>).
+
+Traditionaly computer data has been moved around in 8-bit chunks
+often called "bytes". These chunks are also known as "octets" in
+networking standards. Perl is widely used to manipulate data of
+many types - not only strings of characters representing human or
+computer languages but also "binary" data being the machines representation
+of numbers, pixels in an image - or just about anything.
+
+When perl is processing "binary data" the programmer wants perl to process
+"sequences of bytes". This is not a problem for perl - as a byte has 256
+possible values it easily fits in perl's much larger "logical character".
+
+=head2 TERMINOLOGY
+
+=over
+
+=item *
+
+I<character>: a character in the range 0..(2**32-1) (or more).
+(What perl's strings are made of.)
+
+=item *
+
+I<byte>: a character in the range 0..255
+(A special case of a perl character.)
+
+=item *
+
+I<octet>: 8 bits of data, with ordinal values 0..255
+(Term for bytes passed to or from a non-perl context, e.g. disk file.)
+
+=back
+
+The marker [INTERNAL] marks Internal Implementation Details, in
+general meant only for those who think they know what they are doing,
+and such details may change in future releases.
+
+=head1 ENCODINGS
+
+=head2 Characteristics of an Encoding
+
+An encoding has a "repertoire" of characters that it can represent,
+and for each representable character there is at least one sequence of
+octets that represents it.
+
+=head2 Types of Encodings
+
+Encodings can be divided into the following types:
+
+=over 4
+
+=item * Fixed length 8-bit (or less) encodings.
+
+Each character is a single octet so may have a repertoire of up to
+256 characters. ASCII and iso-8859-* are typical examples.
+
+=item * Fixed length 16-bit encodings
+
+Each character is two octets so may have a repertoire of up to
+65,536 characters. Unicode's UCS-2 is an example. Also used for
+encodings for East Asian languages.
+
+=item * Fixed length 32-bit encodings.
+
+Not really very "encoded" encodings. The Unicode code points
+are just represented as 4-octet integers. None the less because
+different architectures use different representations of integers
+(so called "endian") there at least two disctinct encodings.
+
+=item * Multi-byte encodings
+
+The number of octets needed to represent a character varies.
+UTF-8 is a particularly complex but regular case of a multi-byte
+encoding. Several East Asian countries use a multi-byte encoding
+where 1-octet is used to cover western roman characters and Asian
+characters get 2-octets.
+(UTF-16 is strictly a multi-byte encoding taking either 2 or 4 octets
+to represent a Unicode code point.)
+
+=item * "Escape" encodings.
+
+These encodings embed "escape sequences" into the octet sequence
+which describe how the following octets are to be interpreted.
+The iso-2022-* family is typical. Following the escape sequence
+octets are encoded by an "embedded" encoding (which will be one
+of the above types) until another escape sequence switches to
+a different "embedded" encoding.
+
+These schemes are very flexible and can handle mixed languages but are
+very complex to process (and have state).
+No escape encodings are implemented for perl yet.
+
+=back
+
+=head2 Specifying Encodings
+
+Encodings can be specified to the API described below in two ways:
+
+=over 4
+
+=item 1. By name
+
+Encoding names are strings with characters taken from a restricted repertoire.
+See L</"Encoding Names">.
+
+=item 2. As an object
+
+Encoding objects are returned by C<find_encoding($name)>.
+
+=back
+
+=head2 Encoding Names
+
+Encoding names are case insensitive. White space in names is ignored.
+In addition an encoding may have aliases. Each encoding has one "canonical" name.
+The "canonical" name is chosen from the names of the encoding by picking
+the first in the following sequence:
+
+=over 4
+
+=item * The MIME name as defined in IETF RFC-XXXX.
+
+=item * The name in the IANA registry.
+
+=item * The name used by the the organization that defined it.
+
+=back
+
+Because of all the alias issues, and because in the general case
+encodings have state C<Encode> uses the encoding object internally
+once an operation is in progress.
+
+I<Aliasing is not yet implemented.>
+
+=head1 PERL ENCODING API
+
+=head2 Generic Encoding Interface
+
+=over 4
+
+=item *
+
+        $bytes  = encode(ENCODING, $string[, CHECK])
+
+Encodes string from perl's internal form into I<ENCODING> and returns a
+sequence of octets.
+See L</"Handling Malformed Data">.
+
+=item *
+
+        $string = decode(ENCODING, $bytes[, CHECK])
+
+Decode sequence of octets assumed to be in I<ENCODING> into perls internal
+form and returns the resuting string.
+See L</"Handling Malformed Data">.
+
+=back
+
+=head2 Handling Malformed Data
+
+If CHECK is not set, C<undef> is returned.  If the data is supposed to
+be UTF-8, an optional lexical warning (category utf8) is given.
+If CHECK is true but not a code reference, dies.
+
+It would desirable to have a way to indicate that transform should use the
+encodings "replacement character" - no such mechanism is defined yet.
+
+It is also planned to allow I<CHECK> to be a code reference.
+
+This is not yet implemented as there are design issues with what its arguments
+should be and how it returns its results.
+
+=over 4
+
+=item Scheme 1
+
+Passed remaining fragment of string being processed.
+Modifies it in place to remove bytes/characters it can understand
+and returns a string used to represent them.
+e.g.
+
+ sub fixup {
+   my $ch = substr($_[0],0,1,'');
+   return sprintf("\x{%02X}",ord($ch);
+ }
+
+This scheme is close to how underlying C code for Encode works, but gives
+the fixup routine very little context.
+
+=item Scheme 2
+
+Passed original string, and an index into it of the problem area,
+and output string so far.
+Appends what it will to output string and returns new index into
+original string.
+e.g.
+
+ sub fixup {
+   # my ($s,$i,$d) = @_;
+   my $ch = substr($_[0],$_[1],1);
+   $_[2] .= sprintf("\x{%02X}",ord($ch);
+   return $_[1]+1;
+ }
+
+This scheme gives maximal control to the fixup routine but is more complicated
+to code, and may need internals of Encode to be tweaked to keep original
+string intact.
+
+=item Other Schemes
+
+Hybrids of above.
+
+Multiple return values rather than in-place modifications.
+
+Index into the string could be pos($str) allowing s/\G...//.
+
+=back
+
+=head2 UTF-8 / utf8
+
+The Unicode consortium defines the UTF-8 standard as a way of encoding
+the entire Unicode repertiore as sequences of octets. This encoding
+is expected to become very widespread. Perl can use this form internaly
+to represent strings, so conversions to and from this form are particularly
+efficient (as octets in memory do not have to change, just the meta-data
+that tells perl how to treat them).
+
+=over 4
+
+=item *
+
+        $bytes = encode_utf8($string);
+
+The characters that comprise string are encoded in perl's superset of UTF-8
+and the resulting octets returned as a sequence of bytes. All possible
+characters have a UTF-8 representation so this function cannot fail.
+
+=item *
+
+        $string = decode_utf8($bytes [,CHECK]);
+
+The sequence of octets represented by $bytes is decoded from UTF-8 into
+a sequence of logical characters. Not all sequences of octets form valid
+UTF-8 encodings, so it is possible for this call to fail.
+See L</"Handling Malformed Data">.
+
+=back
+
+=head2 Other Encodings of Unicode
+
+UTF-16 is similar to UCS-2, 16 bit or 2-byte chunks.
+UCS-2 can only represent 0..0xFFFF, while UTF-16 has a "surogate pair"
+scheme which allows it to cover the whole Unicode range.
+
+Encode implements big-endian UCS-2 as the encoding "iso10646-1" as that
+happens to be the name used by that representation when used with X11 fonts.
+
+UTF-32 or UCS-4 is 32-bit or 4-byte chunks.  Perl's logical characters
+can be considered as being in this form without encoding. An encoding
+to transfer strings in this form (e.g. to write them to a file) would need to
+
+     pack('L',map(chr($_),split(//,$string)));   # native
+  or
+     pack('V',map(chr($_),split(//,$string)));   # little-endian
+  or
+     pack('N',map(chr($_),split(//,$string)));   # big-endian
+
+depending on the endian required.
+
+No UTF-32 encodings are not yet implemented.
+
+Both UCS-2 and UCS-4 style encodings can have "byte order marks" by representing
+the code point 0xFFFE as the very first thing in a file.
+
+=head1 Encoding and IO
+
+It is very common to want to do encoding transformations when
+reading or writing files, network connections, pipes etc.
+If perl is configured to use the new 'perlio' IO system then
+C<Encode> provides a "layer" (See L<perliol>) which can transform
+data as it is read or written.
+
+     open(my $ilyad,'>:encoding(iso8859-7)','ilyad.greek');
+     print $ilyad @epic;
+
+In addition the new IO system can also be configured to read/write
+UTF-8 encoded characters (as noted above this is efficient):
+
+     open(my $fh,'>:utf8','anything');
+     print $fh "Any \x{0021} string \N{SMILEY FACE}\n";
+
+Either of the above forms of "layer" specifications can be made the default
+for a lexical scope with the C<use open ...> pragma. See L<open>.
+
+Once a handle is open is layers can be altered using C<binmode>.
+
+Without any such configuration, or if perl itself is built using
+system's own IO, then write operations assume that file handle accepts
+only I<bytes> and will C<die> if a character larger than 255 is
+written to the handle. When reading, each octet from the handle
+becomes a byte-in-a-character. Note that this default is the same
+behaviour as bytes-only languages (including perl before v5.6) would have,
+and is sufficient to handle native 8-bit encodings e.g. iso-8859-1,
+EBCDIC etc. and any legacy mechanisms for handling other encodings
+and binary data.
+
+In other cases it is the programs responsibility
+to transform characters into bytes using the API above before
+doing writes, and to transform the bytes read from a handle into characters
+before doing "character operations" (e.g. C<lc>, C</\W+/>, ...).
+
+=head1 Encoding How to ...
+
+To do:
+
+=over 4
+
+=item * IO with mixed content (faking iso-2020-*)
+
+=item * MIME's Content-Length:
+
+=item * UTF-8 strings in binary data.
+
+=item * perl/Encode wrappers on non-Unicode XS modules.
+
+=back
+
+=head1 Messing with Perl's Internals
+
+The following API uses parts of perl's internals in the current implementation.
+As such they are efficient, but may change.
+
+=over 4
+
+=item *
+
+        $num_octets = utf8_upgrade($string);
+
+Converts internal representation of string to the UTF-8 form.
+Returns the number of octets necessary to represent the string as UTF-8.
+
+=item * utf8_downgrade($string[, CHECK])
+
+Converts internal representation of string to be un-encoded bytes.
+
+=item * is_utf8(STRING [, CHECK])
+
+[INTERNAL] Test whether the UTF-8 flag is turned on in the STRING.
+If CHECK is true, also checks the data in STRING for being
+well-formed UTF-8.  Returns true if successful, false otherwise.
+
+=item * valid_utf8(STRING)
+
+[INTERNAL] Test whether STRING is in a consistent state.
+Will return true if string is held as bytes, or is well-formed UTF-8
+and has the UTF-8 flag on.
+Main reason for this routine is to allow perl's testsuite to check
+that operations have left strings in a consistent state.
+
+=item *
+
+        _utf8_on(STRING)
+
+[INTERNAL] Turn on the UTF-8 flag in STRING.  The data in STRING is
+B<not> checked for being well-formed UTF-8.  Do not use unless you
+B<know> that the STRING is well-formed UTF-8.  Returns the previous
+state of the UTF-8 flag (so please don't test the return value as
+I<not> success or failure), or C<undef> if STRING is not a string.
+
+=item *
+
+        _utf8_off(STRING)
+
+[INTERNAL] Turn off the UTF-8 flag in STRING.  Do not use frivolously.
+Returns the previous state of the UTF-8 flag (so please don't test the
+return value as I<not> success or failure), or C<undef> if STRING is
+not a string.
+
+=back
+
+=head1 SEE ALSO
+
+L<perlunicode>, L<perlebcdic>, L<perlfunc/open>
+
+=cut
+
+
 __END__
diff --git a/ext/Encode/Encode.xs b/ext/Encode/Encode.xs
index 8aa51ff33d..3913fafb48 100644
--- a/ext/Encode/Encode.xs
+++ b/ext/Encode/Encode.xs
@@ -453,7 +453,7 @@ bool
 sv_utf8_decode(sv)
 SV *	sv
 
-void
+STRLEN
 sv_utf8_upgrade(sv)
 SV *	sv
 
@@ -584,88 +584,16 @@ _utf8_to_bytes(sv, ...)
       OUTPUT:
 	RETVAL
 
-SV *
-_chars_to_utf8(sv, from, ...)
-	SV *	sv
-	SV *	from
-      CODE:
-	{
-	  SV * check = items == 3 ? ST(2) : Nullsv;
-	  RETVAL = &PL_sv_undef;
-	}
-      OUTPUT:
-	RETVAL
-
-SV *
-_utf8_to_chars(sv, to, ...)
-	SV *	sv
-	SV *	to
-      CODE:
-	{
-	  SV * check = items == 3 ? ST(2) : Nullsv;
-	  RETVAL = &PL_sv_undef;
-	}
-      OUTPUT:
-	RETVAL
-
-SV *
-_utf8_to_chars_check(sv, ...)
-	SV *	sv
-      CODE:
-	{
-	  SV * check = items == 2 ? ST(1) : Nullsv;
-	  RETVAL = &PL_sv_undef;
-	}
-      OUTPUT:
-	RETVAL
-
-SV *
-_bytes_to_chars(sv, from, ...)
-	SV *	sv
-	SV *	from
-      CODE:
-	{
-	  SV * check = items == 3 ? ST(2) : Nullsv;
-	  RETVAL = &PL_sv_undef;
-	}
-      OUTPUT:
-	RETVAL
-
-SV *
-_chars_to_bytes(sv, to, ...)
-	SV *	sv
-	SV *	to
-      CODE:
-	{
-	  SV * check = items == 3 ? ST(2) : Nullsv;
-	  RETVAL = &PL_sv_undef;
-	}
-      OUTPUT:
-	RETVAL
-
-SV *
-_from_to(sv, from, to, ...)
-	SV *	sv
-	SV *	from
-	SV *	to
-      CODE:
-	{
-	  SV * check = items == 4 ? ST(3) : Nullsv;
-	  RETVAL = &PL_sv_undef;
-	}
-      OUTPUT:
-	RETVAL
-
 bool
-_is_utf8(sv, ...)
-	SV *	sv
+is_utf8(sv, check = FALSE)
+SV *	sv
+bool	check
       CODE:
 	{
-	  SV *	check = items == 2 ? ST(1) : Nullsv;
 	  if (SvPOK(sv)) {
-	    RETVAL = SvUTF8(sv) ? 1 : 0;
+	    RETVAL = SvUTF8(sv) ? TRUE : FALSE;
 	    if (RETVAL &&
-		SvTRUE(check) &&
+		check  &&
 		!is_utf8_string((U8*)SvPVX(sv), SvCUR(sv)))
 	      RETVAL = FALSE;
 	  } else {
@@ -676,7 +604,7 @@ _is_utf8(sv, ...)
 	RETVAL
 
 SV *
-_on_utf8(sv)
+_utf8_on(sv)
 	SV *	sv
       CODE:
 	{
@@ -692,7 +620,7 @@ _on_utf8(sv)
 	RETVAL
 
 SV *
-_off_utf8(sv)
+_utf8_off(sv)
 	SV *	sv
       CODE:
 	{
@@ -707,19 +635,6 @@ _off_utf8(sv)
       OUTPUT:
 	RETVAL
 
-SV *
-_utf_to_utf(sv, from, to, ...)
-	SV *	sv
-	SV *	from
-	SV *	to
-      CODE:
-	{
-	  SV * check = items == 4 ? ST(3) : Nullsv;
-	  RETVAL = &PL_sv_undef;
-	}
-      OUTPUT:
-	RETVAL
-
 BOOT:
 {
 #ifdef USE_PERLIO