infnan: the nan quiet/signaling bit is not enough

[perl5.git] / utf8.c

/*    utf8.c
 *
 *    Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008
 *    by Larry Wall and others
 *
 *    You may distribute under the terms of either the GNU General Public
 *    License or the Artistic License, as specified in the README file.
 *
 */

/*
 * 'What a fix!' said Sam.  'That's the one place in all the lands we've ever
 *  heard of that we don't want to see any closer; and that's the one place
 *  we're trying to get to!  And that's just where we can't get, nohow.'
 *
 *     [p.603 of _The Lord of the Rings_, IV/I: "The Taming of Sméagol"]
 *
 * 'Well do I understand your speech,' he answered in the same language;
 * 'yet few strangers do so.  Why then do you not speak in the Common Tongue,
 *  as is the custom in the West, if you wish to be answered?'
 *                           --Gandalf, addressing Théoden's door wardens
 *
 *     [p.508 of _The Lord of the Rings_, III/vi: "The King of the Golden Hall"]
 *
 * ...the travellers perceived that the floor was paved with stones of many
 * hues; branching runes and strange devices intertwined beneath their feet.
 *
 *     [p.512 of _The Lord of the Rings_, III/vi: "The King of the Golden Hall"]
 */

#include "EXTERN.h"
#define PERL_IN_UTF8_C
#include "perl.h"
#include "inline_invlist.c"
#include "charclass_invlists.h"

static const char unees[] =
    "Malformed UTF-8 character (unexpected end of string)";

/*
=head1 Unicode Support
These are various utility functions for manipulating UTF8-encoded
strings.  For the uninitiated, this is a method of representing arbitrary
Unicode characters as a variable number of bytes, in such a way that
characters in the ASCII range are unmodified, and a zero byte never appears
within non-zero characters.

=cut
*/

/*
=for apidoc is_invariant_string

Returns true iff the first C<len> bytes of the string C<s> are the same
regardless of the UTF-8 encoding of the string (or UTF-EBCDIC encoding on
EBCDIC machines).  That is, if they are UTF-8 invariant.  On ASCII-ish
machines, all the ASCII characters and only the ASCII characters fit this
definition.  On EBCDIC machines, the ASCII-range characters are invariant, but
so also are the C1 controls and C<\c?> (which isn't in the ASCII range on
EBCDIC).

If C<len> is 0, it will be calculated using C<strlen(s)>, (which means if you
use this option, that C<s> can't have embedded C<NUL> characters and has to
have a terminating C<NUL> byte).

See also L</is_utf8_string>(), L</is_utf8_string_loclen>(), and L</is_utf8_string_loc>().

=cut
*/

bool
Perl_is_invariant_string(const U8 *s, STRLEN len)
{
    const U8* const send = s + (len ? len : strlen((const char *)s));
    const U8* x = s;

    PERL_ARGS_ASSERT_IS_INVARIANT_STRING;

    for (; x < send; ++x) {
        if (!UTF8_IS_INVARIANT(*x))
            break;
    }

    return x == send;
}

/*
=for apidoc uvoffuni_to_utf8_flags

THIS FUNCTION SHOULD BE USED IN ONLY VERY SPECIALIZED CIRCUMSTANCES.
Instead, B<Almost all code should use L</uvchr_to_utf8> or
L</uvchr_to_utf8_flags>>.

This function is like them, but the input is a strict Unicode
(as opposed to native) code point.  Only in very rare circumstances should code
not be using the native code point.

For details, see the description for L</uvchr_to_utf8_flags>>.

=cut
*/

U8 *
Perl_uvoffuni_to_utf8_flags(pTHX_ U8 *d, UV uv, UV flags)
{
    PERL_ARGS_ASSERT_UVOFFUNI_TO_UTF8_FLAGS;

    if (UNI_IS_INVARIANT(uv)) {
        *d++ = (U8) LATIN1_TO_NATIVE(uv);
        return d;
    }

#ifdef EBCDIC
    /* Not representable in UTF-EBCDIC */
    flags |= UNICODE_DISALLOW_FE_FF;
#endif

    /* The first problematic code point is the first surrogate */
    if (uv >= UNICODE_SURROGATE_FIRST
        && ckWARN3_d(WARN_SURROGATE, WARN_NON_UNICODE, WARN_NONCHAR))
    {
        if (UNICODE_IS_SURROGATE(uv)) {
            if (flags & UNICODE_WARN_SURROGATE) {
                Perl_ck_warner_d(aTHX_ packWARN(WARN_SURROGATE),
                                            "UTF-16 surrogate U+%04"UVXf, uv);
            }
            if (flags & UNICODE_DISALLOW_SURROGATE) {
                return NULL;
            }
        }
        else if (UNICODE_IS_SUPER(uv)) {
            if (flags & UNICODE_WARN_SUPER
                || (UNICODE_IS_FE_FF(uv) && (flags & UNICODE_WARN_FE_FF)))
            {
                Perl_ck_warner_d(aTHX_ packWARN(WARN_NON_UNICODE),
                          "Code point 0x%04"UVXf" is not Unicode, may not be portable", uv);
            }
            if (flags & UNICODE_DISALLOW_SUPER
                || (UNICODE_IS_FE_FF(uv) && (flags & UNICODE_DISALLOW_FE_FF)))
            {
#ifdef EBCDIC
                Perl_die(aTHX_ "Can't represent character for Ox%"UVXf" on this platform", uv);
                NOT_REACHED;
#endif
                return NULL;
            }
        }
        else if (UNICODE_IS_NONCHAR(uv)) {
            if (flags & UNICODE_WARN_NONCHAR) {
                Perl_ck_warner_d(aTHX_ packWARN(WARN_NONCHAR),
                 "Unicode non-character U+%04"UVXf" is illegal for open interchange",
                 uv);
            }
            if (flags & UNICODE_DISALLOW_NONCHAR) {
                return NULL;
            }
        }
    }

#if defined(EBCDIC)
    {
        STRLEN len  = OFFUNISKIP(uv);
        U8 *p = d+len-1;
        while (p > d) {
            *p-- = (U8) I8_TO_NATIVE_UTF8((uv & UTF_CONTINUATION_MASK) | UTF_CONTINUATION_MARK);
            uv >>= UTF_ACCUMULATION_SHIFT;
        }
        *p = (U8) I8_TO_NATIVE_UTF8((uv & UTF_START_MASK(len)) | UTF_START_MARK(len));
        return d+len;
    }
#else /* Non loop style */
    if (uv < 0x800) {
        *d++ = (U8)(( uv >>  6)         | 0xc0);
        *d++ = (U8)(( uv        & 0x3f) | 0x80);
        return d;
    }
    if (uv < 0x10000) {
        *d++ = (U8)(( uv >> 12)         | 0xe0);
        *d++ = (U8)(((uv >>  6) & 0x3f) | 0x80);
        *d++ = (U8)(( uv        & 0x3f) | 0x80);
        return d;
    }
    if (uv < 0x200000) {
        *d++ = (U8)(( uv >> 18)         | 0xf0);
        *d++ = (U8)(((uv >> 12) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >>  6) & 0x3f) | 0x80);
        *d++ = (U8)(( uv        & 0x3f) | 0x80);
        return d;
    }
    if (uv < 0x4000000) {
        *d++ = (U8)(( uv >> 24)         | 0xf8);
        *d++ = (U8)(((uv >> 18) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 12) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >>  6) & 0x3f) | 0x80);
        *d++ = (U8)(( uv        & 0x3f) | 0x80);
        return d;
    }
    if (uv < 0x80000000) {
        *d++ = (U8)(( uv >> 30)         | 0xfc);
        *d++ = (U8)(((uv >> 24) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 18) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 12) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >>  6) & 0x3f) | 0x80);
        *d++ = (U8)(( uv        & 0x3f) | 0x80);
        return d;
    }
#ifdef UTF8_QUAD_MAX
    if (uv < UTF8_QUAD_MAX)
#endif
    {
        *d++ =                            0xfe; /* Can't match U+FEFF! */
        *d++ = (U8)(((uv >> 30) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 24) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 18) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 12) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >>  6) & 0x3f) | 0x80);
        *d++ = (U8)(( uv        & 0x3f) | 0x80);
        return d;
    }
#ifdef UTF8_QUAD_MAX
    {
        *d++ =                            0xff;         /* Can't match U+FFFE! */
        *d++ =                            0x80;         /* 6 Reserved bits */
        *d++ = (U8)(((uv >> 60) & 0x0f) | 0x80);        /* 2 Reserved bits */
        *d++ = (U8)(((uv >> 54) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 48) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 42) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 36) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 30) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 24) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 18) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >> 12) & 0x3f) | 0x80);
        *d++ = (U8)(((uv >>  6) & 0x3f) | 0x80);
        *d++ = (U8)(( uv        & 0x3f) | 0x80);
        return d;
    }
#endif
#endif /* Non loop style */
}
/*
=for apidoc uvchr_to_utf8

Adds the UTF-8 representation of the native code point C<uv> to the end
of the string C<d>; C<d> should have at least C<UNISKIP(uv)+1> (up to
C<UTF8_MAXBYTES+1>) free bytes available.  The return value is the pointer to
the byte after the end of the new character.  In other words,

    d = uvchr_to_utf8(d, uv);

is the recommended wide native character-aware way of saying

    *(d++) = uv;

This function accepts any UV as input.  To forbid or warn on non-Unicode code
points, or those that may be problematic, see L</uvchr_to_utf8_flags>.

=cut
*/

/* This is also a macro */
PERL_CALLCONV U8*       Perl_uvchr_to_utf8(pTHX_ U8 *d, UV uv);

U8 *
Perl_uvchr_to_utf8(pTHX_ U8 *d, UV uv)
{
    return uvchr_to_utf8(d, uv);
}

/*
=for apidoc uvchr_to_utf8_flags

Adds the UTF-8 representation of the native code point C<uv> to the end
of the string C<d>; C<d> should have at least C<UNISKIP(uv)+1> (up to
C<UTF8_MAXBYTES+1>) free bytes available.  The return value is the pointer to
the byte after the end of the new character.  In other words,

    d = uvchr_to_utf8_flags(d, uv, flags);

or, in most cases,

    d = uvchr_to_utf8_flags(d, uv, 0);

This is the Unicode-aware way of saying

    *(d++) = uv;

This function will convert to UTF-8 (and not warn) even code points that aren't
legal Unicode or are problematic, unless C<flags> contains one or more of the
following flags:

If C<uv> is a Unicode surrogate code point and UNICODE_WARN_SURROGATE is set,
the function will raise a warning, provided UTF8 warnings are enabled.  If instead
UNICODE_DISALLOW_SURROGATE is set, the function will fail and return NULL.
If both flags are set, the function will both warn and return NULL.

The UNICODE_WARN_NONCHAR and UNICODE_DISALLOW_NONCHAR flags
affect how the function handles a Unicode non-character.  And likewise, the
UNICODE_WARN_SUPER and UNICODE_DISALLOW_SUPER flags affect the handling of
code points that are
above the Unicode maximum of 0x10FFFF.  Code points above 0x7FFF_FFFF (which are
even less portable) can be warned and/or disallowed even if other above-Unicode
code points are accepted, by the UNICODE_WARN_FE_FF and UNICODE_DISALLOW_FE_FF
flags.

And finally, the flag UNICODE_WARN_ILLEGAL_INTERCHANGE selects all four of the
above WARN flags; and UNICODE_DISALLOW_ILLEGAL_INTERCHANGE selects all four
DISALLOW flags.

=cut
*/

/* This is also a macro */
PERL_CALLCONV U8*       Perl_uvchr_to_utf8_flags(pTHX_ U8 *d, UV uv, UV flags);

U8 *
Perl_uvchr_to_utf8_flags(pTHX_ U8 *d, UV uv, UV flags)
{
    return uvchr_to_utf8_flags(d, uv, flags);
}

/*
=for apidoc is_utf8_string

Returns true if the first C<len> bytes of string C<s> form a valid
UTF-8 string, false otherwise.  If C<len> is 0, it will be calculated
using C<strlen(s)> (which means if you use this option, that C<s> can't have
embedded C<NUL> characters and has to have a terminating C<NUL> byte).  Note
that all characters being ASCII constitute 'a valid UTF-8 string'.

See also L</is_invariant_string>(), L</is_utf8_string_loclen>(), and L</is_utf8_string_loc>().

=cut
*/

bool
Perl_is_utf8_string(const U8 *s, STRLEN len)
{
    const U8* const send = s + (len ? len : strlen((const char *)s));
    const U8* x = s;

    PERL_ARGS_ASSERT_IS_UTF8_STRING;

    while (x < send) {
        STRLEN len = isUTF8_CHAR(x, send);
        if (UNLIKELY(! len)) {
            return FALSE;
        }
        x += len;
    }

    return TRUE;
}

/*
Implemented as a macro in utf8.h

=for apidoc is_utf8_string_loc

Like L</is_utf8_string> but stores the location of the failure (in the
case of "utf8ness failure") or the location C<s>+C<len> (in the case of
"utf8ness success") in the C<ep>.

See also L</is_utf8_string_loclen>() and L</is_utf8_string>().

=for apidoc is_utf8_string_loclen

Like L</is_utf8_string>() but stores the location of the failure (in the
case of "utf8ness failure") or the location C<s>+C<len> (in the case of
"utf8ness success") in the C<ep>, and the number of UTF-8
encoded characters in the C<el>.

See also L</is_utf8_string_loc>() and L</is_utf8_string>().

=cut
*/

bool
Perl_is_utf8_string_loclen(const U8 *s, STRLEN len, const U8 **ep, STRLEN *el)
{
    const U8* const send = s + (len ? len : strlen((const char *)s));
    const U8* x = s;
    STRLEN outlen = 0;

    PERL_ARGS_ASSERT_IS_UTF8_STRING_LOCLEN;

    while (x < send) {
        STRLEN len = isUTF8_CHAR(x, send);
        if (UNLIKELY(! len)) {
            goto out;
        }
        x += len;
        outlen++;
    }

 out:
    if (el)
        *el = outlen;

    if (ep)
        *ep = x;
    return (x == send);
}

/*

=for apidoc utf8n_to_uvchr

THIS FUNCTION SHOULD BE USED IN ONLY VERY SPECIALIZED CIRCUMSTANCES.
Most code should use L</utf8_to_uvchr_buf>() rather than call this directly.

Bottom level UTF-8 decode routine.
Returns the native code point value of the first character in the string C<s>,
which is assumed to be in UTF-8 (or UTF-EBCDIC) encoding, and no longer than
C<curlen> bytes; C<*retlen> (if C<retlen> isn't NULL) will be set to
the length, in bytes, of that character.

The value of C<flags> determines the behavior when C<s> does not point to a
well-formed UTF-8 character.  If C<flags> is 0, when a malformation is found,
zero is returned and C<*retlen> is set so that (S<C<s> + C<*retlen>>) is the
next possible position in C<s> that could begin a non-malformed character.
Also, if UTF-8 warnings haven't been lexically disabled, a warning is raised.

Various ALLOW flags can be set in C<flags> to allow (and not warn on)
individual types of malformations, such as the sequence being overlong (that
is, when there is a shorter sequence that can express the same code point;
overlong sequences are expressly forbidden in the UTF-8 standard due to
potential security issues).  Another malformation example is the first byte of
a character not being a legal first byte.  See F<utf8.h> for the list of such
flags.  For allowed 0 length strings, this function returns 0; for allowed
overlong sequences, the computed code point is returned; for all other allowed
malformations, the Unicode REPLACEMENT CHARACTER is returned, as these have no
determinable reasonable value.

The UTF8_CHECK_ONLY flag overrides the behavior when a non-allowed (by other
flags) malformation is found.  If this flag is set, the routine assumes that
the caller will raise a warning, and this function will silently just set
C<retlen> to C<-1> (cast to C<STRLEN>) and return zero.

Note that this API requires disambiguation between successful decoding a C<NUL>
character, and an error return (unless the UTF8_CHECK_ONLY flag is set), as
in both cases, 0 is returned.  To disambiguate, upon a zero return, see if the
first byte of C<s> is 0 as well.  If so, the input was a C<NUL>; if not, the
input had an error.

Certain code points are considered problematic.  These are Unicode surrogates,
Unicode non-characters, and code points above the Unicode maximum of 0x10FFFF.
By default these are considered regular code points, but certain situations
warrant special handling for them.  If C<flags> contains
UTF8_DISALLOW_ILLEGAL_INTERCHANGE, all three classes are treated as
malformations and handled as such.  The flags UTF8_DISALLOW_SURROGATE,
UTF8_DISALLOW_NONCHAR, and UTF8_DISALLOW_SUPER (meaning above the legal Unicode
maximum) can be set to disallow these categories individually.

The flags UTF8_WARN_ILLEGAL_INTERCHANGE, UTF8_WARN_SURROGATE,
UTF8_WARN_NONCHAR, and UTF8_WARN_SUPER will cause warning messages to be raised
for their respective categories, but otherwise the code points are considered
valid (not malformations).  To get a category to both be treated as a
malformation and raise a warning, specify both the WARN and DISALLOW flags.
(But note that warnings are not raised if lexically disabled nor if
UTF8_CHECK_ONLY is also specified.)

Very large code points (above 0x7FFF_FFFF) are considered more problematic than
the others that are above the Unicode legal maximum.  There are several
reasons: they requre at least 32 bits to represent them on ASCII platforms, are
not representable at all on EBCDIC platforms, and the original UTF-8
specification never went above this number (the current 0x10FFFF limit was
imposed later).  (The smaller ones, those that fit into 32 bits, are
representable by a UV on ASCII platforms, but not by an IV, which means that
the number of operations that can be performed on them is quite restricted.)
The UTF-8 encoding on ASCII platforms for these large code points begins with a
byte containing 0xFE or 0xFF.  The UTF8_DISALLOW_FE_FF flag will cause them to
be treated as malformations, while allowing smaller above-Unicode code points.
(Of course UTF8_DISALLOW_SUPER will treat all above-Unicode code points,
including these, as malformations.)
Similarly, UTF8_WARN_FE_FF acts just like
the other WARN flags, but applies just to these code points.

All other code points corresponding to Unicode characters, including private
use and those yet to be assigned, are never considered malformed and never
warn.

=cut
*/

UV
Perl_utf8n_to_uvchr(pTHX_ const U8 *s, STRLEN curlen, STRLEN *retlen, U32 flags)
{
    const U8 * const s0 = s;
    U8 overflow_byte = '\0';    /* Save byte in case of overflow */
    U8 * send;
    UV uv = *s;
    STRLEN expectlen;
    SV* sv = NULL;
    UV outlier_ret = 0; /* return value when input is in error or problematic
                         */
    UV pack_warn = 0;   /* Save result of packWARN() for later */
    bool unexpected_non_continuation = FALSE;
    bool overflowed = FALSE;
    bool do_overlong_test = TRUE;   /* May have to skip this test */

    const char* const malformed_text = "Malformed UTF-8 character";

    PERL_ARGS_ASSERT_UTF8N_TO_UVCHR;

    /* The order of malformation tests here is important.  We should consume as
     * few bytes as possible in order to not skip any valid character.  This is
     * required by the Unicode Standard (section 3.9 of Unicode 6.0); see also
     * http://unicode.org/reports/tr36 for more discussion as to why.  For
     * example, once we've done a UTF8SKIP, we can tell the expected number of
     * bytes, and could fail right off the bat if the input parameters indicate
     * that there are too few available.  But it could be that just that first
     * byte is garbled, and the intended character occupies fewer bytes.  If we
     * blindly assumed that the first byte is correct, and skipped based on
     * that number, we could skip over a valid input character.  So instead, we
     * always examine the sequence byte-by-byte.
     *
     * We also should not consume too few bytes, otherwise someone could inject
     * things.  For example, an input could be deliberately designed to
     * overflow, and if this code bailed out immediately upon discovering that,
     * returning to the caller C<*retlen> pointing to the very next byte (one
     * which is actually part of of the overflowing sequence), that could look
     * legitimate to the caller, which could discard the initial partial
     * sequence and process the rest, inappropriately */

    /* Zero length strings, if allowed, of necessity are zero */
    if (UNLIKELY(curlen == 0)) {
        if (retlen) {
            *retlen = 0;
        }

        if (flags & UTF8_ALLOW_EMPTY) {
            return 0;
        }
        if (! (flags & UTF8_CHECK_ONLY)) {
            sv = sv_2mortal(Perl_newSVpvf(aTHX_ "%s (empty string)", malformed_text));
        }
        goto malformed;
    }

    expectlen = UTF8SKIP(s);

    /* A well-formed UTF-8 character, as the vast majority of calls to this
     * function will be for, has this expected length.  For efficiency, set
     * things up here to return it.  It will be overriden only in those rare
     * cases where a malformation is found */
    if (retlen) {
        *retlen = expectlen;
    }

    /* An invariant is trivially well-formed */
    if (UTF8_IS_INVARIANT(uv)) {
        return uv;
    }

    /* A continuation character can't start a valid sequence */
    if (UNLIKELY(UTF8_IS_CONTINUATION(uv))) {
        if (flags & UTF8_ALLOW_CONTINUATION) {
            if (retlen) {
                *retlen = 1;
            }
            return UNICODE_REPLACEMENT;
        }

        if (! (flags & UTF8_CHECK_ONLY)) {
            sv = sv_2mortal(Perl_newSVpvf(aTHX_ "%s (unexpected continuation byte 0x%02x, with no preceding start byte)", malformed_text, *s0));
        }
        curlen = 1;
        goto malformed;
    }

    /* Here is not a continuation byte, nor an invariant.  The only thing left
     * is a start byte (possibly for an overlong) */

#ifdef EBCDIC
    uv = NATIVE_UTF8_TO_I8(uv);
#endif

    /* Remove the leading bits that indicate the number of bytes in the
     * character's whole UTF-8 sequence, leaving just the bits that are part of
     * the value */
    uv &= UTF_START_MASK(expectlen);

    /* Now, loop through the remaining bytes in the character's sequence,
     * accumulating each into the working value as we go.  Be sure to not look
     * past the end of the input string */
    send =  (U8*) s0 + ((expectlen <= curlen) ? expectlen : curlen);

    for (s = s0 + 1; s < send; s++) {
        if (LIKELY(UTF8_IS_CONTINUATION(*s))) {
#ifndef EBCDIC  /* Can't overflow in EBCDIC */
            if (uv & UTF_ACCUMULATION_OVERFLOW_MASK) {

                /* The original implementors viewed this malformation as more
                 * serious than the others (though I, khw, don't understand
                 * why, since other malformations also give very very wrong
                 * results), so there is no way to turn off checking for it.
                 * Set a flag, but keep going in the loop, so that we absorb
                 * the rest of the bytes that comprise the character. */
                overflowed = TRUE;
                overflow_byte = *s; /* Save for warning message's use */
            }
#endif
            uv = UTF8_ACCUMULATE(uv, *s);
        }
        else {
            /* Here, found a non-continuation before processing all expected
             * bytes.  This byte begins a new character, so quit, even if
             * allowing this malformation. */
            unexpected_non_continuation = TRUE;
            break;
        }
    } /* End of loop through the character's bytes */

    /* Save how many bytes were actually in the character */
    curlen = s - s0;

    /* The loop above finds two types of malformations: non-continuation and/or
     * overflow.  The non-continuation malformation is really a too-short
     * malformation, as it means that the current character ended before it was
     * expected to (being terminated prematurely by the beginning of the next
     * character, whereas in the too-short malformation there just are too few
     * bytes available to hold the character.  In both cases, the check below
     * that we have found the expected number of bytes would fail if executed.)
     * Thus the non-continuation malformation is really unnecessary, being a
     * subset of the too-short malformation.  But there may be existing
     * applications that are expecting the non-continuation type, so we retain
     * it, and return it in preference to the too-short malformation.  (If this
     * code were being written from scratch, the two types might be collapsed
     * into one.)  I, khw, am also giving priority to returning the
     * non-continuation and too-short malformations over overflow when multiple
     * ones are present.  I don't know of any real reason to prefer one over
     * the other, except that it seems to me that multiple-byte errors trumps
     * errors from a single byte */
    if (UNLIKELY(unexpected_non_continuation)) {
        if (!(flags & UTF8_ALLOW_NON_CONTINUATION)) {
            if (! (flags & UTF8_CHECK_ONLY)) {
                if (curlen == 1) {
                    sv = sv_2mortal(Perl_newSVpvf(aTHX_ "%s (unexpected non-continuation byte 0x%02x, immediately after start byte 0x%02x)", malformed_text, *s, *s0));
                }
                else {
                    sv = sv_2mortal(Perl_newSVpvf(aTHX_ "%s (unexpected non-continuation byte 0x%02x, %d bytes after start byte 0x%02x, expected %d bytes)", malformed_text, *s, (int) curlen, *s0, (int)expectlen));
                }
            }
            goto malformed;
        }
        uv = UNICODE_REPLACEMENT;

        /* Skip testing for overlongs, as the REPLACEMENT may not be the same
         * as what the original expectations were. */
        do_overlong_test = FALSE;
        if (retlen) {
            *retlen = curlen;
        }
    }
    else if (UNLIKELY(curlen < expectlen)) {
        if (! (flags & UTF8_ALLOW_SHORT)) {
            if (! (flags & UTF8_CHECK_ONLY)) {
                sv = sv_2mortal(Perl_newSVpvf(aTHX_ "%s (%d byte%s, need %d, after start byte 0x%02x)", malformed_text, (int)curlen, curlen == 1 ? "" : "s", (int)expectlen, *s0));
            }
            goto malformed;
        }
        uv = UNICODE_REPLACEMENT;
        do_overlong_test = FALSE;
        if (retlen) {
            *retlen = curlen;
        }
    }

#ifndef EBCDIC  /* EBCDIC can't overflow */
    if (UNLIKELY(overflowed)) {
        sv = sv_2mortal(Perl_newSVpvf(aTHX_ "%s (overflow at byte 0x%02x, after start byte 0x%02x)", malformed_text, overflow_byte, *s0));
        goto malformed;
    }
#endif

    if (do_overlong_test
        && expectlen > (STRLEN) OFFUNISKIP(uv)
        && ! (flags & UTF8_ALLOW_LONG))
    {
        /* The overlong malformation has lower precedence than the others.
         * Note that if this malformation is allowed, we return the actual
         * value, instead of the replacement character.  This is because this
         * value is actually well-defined. */
        if (! (flags & UTF8_CHECK_ONLY)) {
            sv = sv_2mortal(Perl_newSVpvf(aTHX_ "%s (%d byte%s, need %d, after start byte 0x%02x)", malformed_text, (int)expectlen, expectlen == 1 ? "": "s", OFFUNISKIP(uv), *s0));
        }
        goto malformed;
    }

    /* Here, the input is considered to be well-formed, but it still could be a
     * problematic code point that is not allowed by the input parameters. */
    if (uv >= UNICODE_SURROGATE_FIRST /* isn't problematic if < this */
        && (flags & (UTF8_DISALLOW_ILLEGAL_INTERCHANGE
                     |UTF8_WARN_ILLEGAL_INTERCHANGE)))
    {
        if (UNICODE_IS_SURROGATE(uv)) {

            /* By adding UTF8_CHECK_ONLY to the test, we avoid unnecessary
             * generation of the sv, since no warnings are raised under CHECK */
            if ((flags & (UTF8_WARN_SURROGATE|UTF8_CHECK_ONLY)) == UTF8_WARN_SURROGATE
                && ckWARN_d(WARN_SURROGATE))
            {
                sv = sv_2mortal(Perl_newSVpvf(aTHX_ "UTF-16 surrogate U+%04"UVXf"", uv));
                pack_warn = packWARN(WARN_SURROGATE);
            }
            if (flags & UTF8_DISALLOW_SURROGATE) {
                goto disallowed;
            }
        }
        else if ((uv > PERL_UNICODE_MAX)) {
            if ((flags & (UTF8_WARN_SUPER|UTF8_CHECK_ONLY)) == UTF8_WARN_SUPER
                && ckWARN_d(WARN_NON_UNICODE))
            {
                sv = sv_2mortal(Perl_newSVpvf(aTHX_ "Code point 0x%04"UVXf" is not Unicode, may not be portable", uv));
                pack_warn = packWARN(WARN_NON_UNICODE);
            }
#ifndef EBCDIC  /* EBCDIC always allows FE, FF */

            /* The first byte being 0xFE or 0xFF is a subset of the SUPER code
             * points.  We test for these after the regular SUPER ones, and
             * before possibly bailing out, so that the more dire warning
             * overrides the regular one, if applicable */
            if ((*s0 & 0xFE) == 0xFE    /* matches both FE, FF */
                && (flags & (UTF8_WARN_FE_FF|UTF8_DISALLOW_FE_FF)))
            {
                if ((flags & (UTF8_WARN_FE_FF|UTF8_CHECK_ONLY))
                                                            == UTF8_WARN_FE_FF
                    && ckWARN_d(WARN_UTF8))
                {
                    sv = sv_2mortal(Perl_newSVpvf(aTHX_ "Code point 0x%"UVXf" is not Unicode, and not portable", uv));
                    pack_warn = packWARN(WARN_UTF8);
                }
                if (flags & UTF8_DISALLOW_FE_FF) {
                    goto disallowed;
                }
            }
#endif
            if (flags & UTF8_DISALLOW_SUPER) {
                goto disallowed;
            }
        }
        else if (UNICODE_IS_NONCHAR(uv)) {
            if ((flags & (UTF8_WARN_NONCHAR|UTF8_CHECK_ONLY)) == UTF8_WARN_NONCHAR
                && ckWARN_d(WARN_NONCHAR))
            {
                sv = sv_2mortal(Perl_newSVpvf(aTHX_ "Unicode non-character U+%04"UVXf" is illegal for open interchange", uv));
                pack_warn = packWARN(WARN_NONCHAR);
            }
            if (flags & UTF8_DISALLOW_NONCHAR) {
                goto disallowed;
            }
        }

        if (sv) {
            outlier_ret = uv;   /* Note we don't bother to convert to native,
                                   as all the outlier code points are the same
                                   in both ASCII and EBCDIC */
            goto do_warn;
        }

        /* Here, this is not considered a malformed character, so drop through
         * to return it */
    }

    return UNI_TO_NATIVE(uv);

    /* There are three cases which get to beyond this point.  In all 3 cases:
     * <sv>         if not null points to a string to print as a warning.
     * <curlen>     is what <*retlen> should be set to if UTF8_CHECK_ONLY isn't
     *              set.
     * <outlier_ret> is what return value to use if UTF8_CHECK_ONLY isn't set.
     *              This is done by initializing it to 0, and changing it only
     *              for case 1).
     * The 3 cases are:
     * 1)   The input is valid but problematic, and to be warned about.  The
     *      return value is the resultant code point; <*retlen> is set to
     *      <curlen>, the number of bytes that comprise the code point.
     *      <pack_warn> contains the result of packWARN() for the warning
     *      types.  The entry point for this case is the label <do_warn>;
     * 2)   The input is a valid code point but disallowed by the parameters to
     *      this function.  The return value is 0.  If UTF8_CHECK_ONLY is set,
     *      <*relen> is -1; otherwise it is <curlen>, the number of bytes that
     *      comprise the code point.  <pack_warn> contains the result of
     *      packWARN() for the warning types.  The entry point for this case is
     *      the label <disallowed>.
     * 3)   The input is malformed.  The return value is 0.  If UTF8_CHECK_ONLY
     *      is set, <*relen> is -1; otherwise it is <curlen>, the number of
     *      bytes that comprise the malformation.  All such malformations are
     *      assumed to be warning type <utf8>.  The entry point for this case
     *      is the label <malformed>.
     */

  malformed:

    if (sv && ckWARN_d(WARN_UTF8)) {
        pack_warn = packWARN(WARN_UTF8);
    }

  disallowed:

    if (flags & UTF8_CHECK_ONLY) {
        if (retlen)
            *retlen = ((STRLEN) -1);
        return 0;
    }

  do_warn:

    if (pack_warn) {    /* <pack_warn> was initialized to 0, and changed only
                           if warnings are to be raised. */
        const char * const string = SvPVX_const(sv);

        if (PL_op)
            Perl_warner(aTHX_ pack_warn, "%s in %s", string,  OP_DESC(PL_op));
        else
            Perl_warner(aTHX_ pack_warn, "%s", string);
    }

    if (retlen) {
        *retlen = curlen;
    }

    return outlier_ret;
}

/*
=for apidoc utf8_to_uvchr_buf

Returns the native code point of the first character in the string C<s> which
is assumed to be in UTF-8 encoding; C<send> points to 1 beyond the end of C<s>.
C<*retlen> will be set to the length, in bytes, of that character.

If C<s> does not point to a well-formed UTF-8 character and UTF8 warnings are
enabled, zero is returned and C<*retlen> is set (if C<retlen> isn't
NULL) to -1.  If those warnings are off, the computed value, if well-defined
(or the Unicode REPLACEMENT CHARACTER if not), is silently returned, and
C<*retlen> is set (if C<retlen> isn't NULL) so that (S<C<s> + C<*retlen>>) is
the next possible position in C<s> that could begin a non-malformed character.
See L</utf8n_to_uvchr> for details on when the REPLACEMENT CHARACTER is
returned.

=cut
*/


UV
Perl_utf8_to_uvchr_buf(pTHX_ const U8 *s, const U8 *send, STRLEN *retlen)
{
    assert(s < send);

    return utf8n_to_uvchr(s, send - s, retlen,
                          ckWARN_d(WARN_UTF8) ? 0 : UTF8_ALLOW_ANY);
}

/* Like L</utf8_to_uvchr_buf>(), but should only be called when it is known that
 * there are no malformations in the input UTF-8 string C<s>.  surrogates,
 * non-character code points, and non-Unicode code points are allowed. */

UV
Perl_valid_utf8_to_uvchr(pTHX_ const U8 *s, STRLEN *retlen)
{
    UV expectlen = UTF8SKIP(s);
    const U8* send = s + expectlen;
    UV uv = *s;

    PERL_ARGS_ASSERT_VALID_UTF8_TO_UVCHR;
    PERL_UNUSED_CONTEXT;

    if (retlen) {
        *retlen = expectlen;
    }

    /* An invariant is trivially returned */
    if (expectlen == 1) {
        return uv;
    }

#ifdef EBCDIC
    uv = NATIVE_UTF8_TO_I8(uv);
#endif

    /* Remove the leading bits that indicate the number of bytes, leaving just
     * the bits that are part of the value */
    uv &= UTF_START_MASK(expectlen);

    /* Now, loop through the remaining bytes, accumulating each into the
     * working total as we go.  (I khw tried unrolling the loop for up to 4
     * bytes, but there was no performance improvement) */
    for (++s; s < send; s++) {
        uv = UTF8_ACCUMULATE(uv, *s);
    }

    return UNI_TO_NATIVE(uv);

}

/*
=for apidoc utf8_to_uvuni_buf

Only in very rare circumstances should code need to be dealing in Unicode
(as opposed to native) code points.  In those few cases, use
C<L<NATIVE_TO_UNI(utf8_to_uvchr_buf(...))|/utf8_to_uvchr_buf>> instead.

Returns the Unicode (not-native) code point of the first character in the
string C<s> which
is assumed to be in UTF-8 encoding; C<send> points to 1 beyond the end of C<s>.
C<retlen> will be set to the length, in bytes, of that character.

If C<s> does not point to a well-formed UTF-8 character and UTF8 warnings are
enabled, zero is returned and C<*retlen> is set (if C<retlen> isn't
NULL) to -1.  If those warnings are off, the computed value if well-defined (or
the Unicode REPLACEMENT CHARACTER, if not) is silently returned, and C<*retlen>
is set (if C<retlen> isn't NULL) so that (S<C<s> + C<*retlen>>) is the
next possible position in C<s> that could begin a non-malformed character.
See L</utf8n_to_uvchr> for details on when the REPLACEMENT CHARACTER is returned.

=cut
*/

UV
Perl_utf8_to_uvuni_buf(pTHX_ const U8 *s, const U8 *send, STRLEN *retlen)
{
    PERL_ARGS_ASSERT_UTF8_TO_UVUNI_BUF;

    assert(send > s);

    /* Call the low level routine asking for checks */
    return NATIVE_TO_UNI(Perl_utf8n_to_uvchr(aTHX_ s, send -s, retlen,
                               ckWARN_d(WARN_UTF8) ? 0 : UTF8_ALLOW_ANY));
}

/*
=for apidoc utf8_length

Return the length of the UTF-8 char encoded string C<s> in characters.
Stops at C<e> (inclusive).  If C<e E<lt> s> or if the scan would end
up past C<e>, croaks.

=cut
*/

STRLEN
Perl_utf8_length(pTHX_ const U8 *s, const U8 *e)
{
    STRLEN len = 0;

    PERL_ARGS_ASSERT_UTF8_LENGTH;

    /* Note: cannot use UTF8_IS_...() too eagerly here since e.g.
     * the bitops (especially ~) can create illegal UTF-8.
     * In other words: in Perl UTF-8 is not just for Unicode. */

    if (e < s)
        goto warn_and_return;
    while (s < e) {
        s += UTF8SKIP(s);
        len++;
    }

    if (e != s) {
        len--;
        warn_and_return:
        if (PL_op)
            Perl_ck_warner_d(aTHX_ packWARN(WARN_UTF8),
                             "%s in %s", unees, OP_DESC(PL_op));
        else
            Perl_ck_warner_d(aTHX_ packWARN(WARN_UTF8), "%s", unees);
    }

    return len;
}

/*
=for apidoc utf8_distance

Returns the number of UTF-8 characters between the UTF-8 pointers C<a>
and C<b>.

WARNING: use only if you *know* that the pointers point inside the
same UTF-8 buffer.

=cut
*/

IV
Perl_utf8_distance(pTHX_ const U8 *a, const U8 *b)
{
    PERL_ARGS_ASSERT_UTF8_DISTANCE;

    return (a < b) ? -1 * (IV) utf8_length(a, b) : (IV) utf8_length(b, a);
}

/*
=for apidoc utf8_hop

Return the UTF-8 pointer C<s> displaced by C<off> characters, either
forward or backward.

WARNING: do not use the following unless you *know* C<off> is within
the UTF-8 data pointed to by C<s> *and* that on entry C<s> is aligned
on the first byte of character or just after the last byte of a character.

=cut
*/

U8 *
Perl_utf8_hop(const U8 *s, I32 off)
{
    PERL_ARGS_ASSERT_UTF8_HOP;

    /* Note: cannot use UTF8_IS_...() too eagerly here since e.g
     * the bitops (especially ~) can create illegal UTF-8.
     * In other words: in Perl UTF-8 is not just for Unicode. */

    if (off >= 0) {
        while (off--)
            s += UTF8SKIP(s);
    }
    else {
        while (off++) {
            s--;
            while (UTF8_IS_CONTINUATION(*s))
                s--;
        }
    }
    return (U8 *)s;
}

/*
=for apidoc bytes_cmp_utf8

Compares the sequence of characters (stored as octets) in C<b>, C<blen> with the
sequence of characters (stored as UTF-8)
in C<u>, C<ulen>.  Returns 0 if they are
equal, -1 or -2 if the first string is less than the second string, +1 or +2
if the first string is greater than the second string.

-1 or +1 is returned if the shorter string was identical to the start of the
longer string.  -2 or +2 is returned if
there was a difference between characters
within the strings.

=cut
*/

int
Perl_bytes_cmp_utf8(pTHX_ const U8 *b, STRLEN blen, const U8 *u, STRLEN ulen)
{
    const U8 *const bend = b + blen;
    const U8 *const uend = u + ulen;

    PERL_ARGS_ASSERT_BYTES_CMP_UTF8;

    while (b < bend && u < uend) {
        U8 c = *u++;
        if (!UTF8_IS_INVARIANT(c)) {
            if (UTF8_IS_DOWNGRADEABLE_START(c)) {
                if (u < uend) {
                    U8 c1 = *u++;
                    if (UTF8_IS_CONTINUATION(c1)) {
                        c = TWO_BYTE_UTF8_TO_NATIVE(c, c1);
                    } else {
                        Perl_ck_warner_d(aTHX_ packWARN(WARN_UTF8),
                                         "Malformed UTF-8 character "
                                         "(unexpected non-continuation byte 0x%02x"
                                         ", immediately after start byte 0x%02x)"
                                         /* Dear diag.t, it's in the pod.  */
                                         "%s%s", c1, c,
                                         PL_op ? " in " : "",
                                         PL_op ? OP_DESC(PL_op) : "");
                        return -2;
                    }
                } else {
                    if (PL_op)
                        Perl_ck_warner_d(aTHX_ packWARN(WARN_UTF8),
                                         "%s in %s", unees, OP_DESC(PL_op));
                    else
                        Perl_ck_warner_d(aTHX_ packWARN(WARN_UTF8), "%s", unees);
                    return -2; /* Really want to return undef :-)  */
                }
            } else {
                return -2;
            }
        }
        if (*b != c) {
            return *b < c ? -2 : +2;
        }
        ++b;
    }

    if (b == bend && u == uend)
        return 0;

    return b < bend ? +1 : -1;
}

/*
=for apidoc utf8_to_bytes

Converts a string C<s> of length C<len> from UTF-8 into native byte encoding.
Unlike L</bytes_to_utf8>, this over-writes the original string, and
updates C<len> to contain the new length.
Returns zero on failure, setting C<len> to -1.

If you need a copy of the string, see L</bytes_from_utf8>.

=cut
*/

U8 *
Perl_utf8_to_bytes(pTHX_ U8 *s, STRLEN *len)
{
    U8 * const save = s;
    U8 * const send = s + *len;
    U8 *d;

    PERL_ARGS_ASSERT_UTF8_TO_BYTES;
    PERL_UNUSED_CONTEXT;

    /* ensure valid UTF-8 and chars < 256 before updating string */
    while (s < send) {
        if (! UTF8_IS_INVARIANT(*s)) {
            if (! UTF8_IS_NEXT_CHAR_DOWNGRADEABLE(s, send)) {
                *len = ((STRLEN) -1);
                return 0;
            }
            s++;
        }
        s++;
    }

    d = s = save;
    while (s < send) {
        U8 c = *s++;
        if (! UTF8_IS_INVARIANT(c)) {
            /* Then it is two-byte encoded */
            c = TWO_BYTE_UTF8_TO_NATIVE(c, *s);
            s++;
        }
        *d++ = c;
    }
    *d = '\0';
    *len = d - save;
    return save;
}

/*
=for apidoc bytes_from_utf8

Converts a string C<s> of length C<len> from UTF-8 into native byte encoding.
Unlike L</utf8_to_bytes> but like L</bytes_to_utf8>, returns a pointer to
the newly-created string, and updates C<len> to contain the new
length.  Returns the original string if no conversion occurs, C<len>
is unchanged.  Do nothing if C<is_utf8> points to 0.  Sets C<is_utf8> to
0 if C<s> is converted or consisted entirely of characters that are invariant
in utf8 (i.e., US-ASCII on non-EBCDIC machines).

=cut
*/

U8 *
Perl_bytes_from_utf8(pTHX_ const U8 *s, STRLEN *len, bool *is_utf8)
{
    U8 *d;
    const U8 *start = s;
    const U8 *send;
    I32 count = 0;

    PERL_ARGS_ASSERT_BYTES_FROM_UTF8;
    PERL_UNUSED_CONTEXT;
    if (!*is_utf8)
        return (U8 *)start;

    /* ensure valid UTF-8 and chars < 256 before converting string */
    for (send = s + *len; s < send;) {
        if (! UTF8_IS_INVARIANT(*s)) {
            if (! UTF8_IS_NEXT_CHAR_DOWNGRADEABLE(s, send)) {
                return (U8 *)start;
            }
            count++;
            s++;
        }
        s++;
    }

    *is_utf8 = FALSE;

    Newx(d, (*len) - count + 1, U8);
    s = start; start = d;
    while (s < send) {
        U8 c = *s++;
        if (! UTF8_IS_INVARIANT(c)) {
            /* Then it is two-byte encoded */
            c = TWO_BYTE_UTF8_TO_NATIVE(c, *s);
            s++;
        }
        *d++ = c;
    }
    *d = '\0';
    *len = d - start;
    return (U8 *)start;
}

/*
=for apidoc bytes_to_utf8

Converts a string C<s> of length C<len> bytes from the native encoding into
UTF-8.
Returns a pointer to the newly-created string, and sets C<len> to
reflect the new length in bytes.

A C<NUL> character will be written after the end of the string.

If you want to convert to UTF-8 from encodings other than
the native (Latin1 or EBCDIC),
see L</sv_recode_to_utf8>().

=cut
*/

/* This logic is duplicated in sv_catpvn_flags, so any bug fixes will
   likewise need duplication. */

U8*
Perl_bytes_to_utf8(pTHX_ const U8 *s, STRLEN *len)
{
    const U8 * const send = s + (*len);
    U8 *d;
    U8 *dst;

    PERL_ARGS_ASSERT_BYTES_TO_UTF8;
    PERL_UNUSED_CONTEXT;

    Newx(d, (*len) * 2 + 1, U8);
    dst = d;

    while (s < send) {
        append_utf8_from_native_byte(*s, &d);
        s++;
    }
    *d = '\0';
    *len = d-dst;
    return dst;
}

/*
 * Convert native (big-endian) or reversed (little-endian) UTF-16 to UTF-8.
 *
 * Destination must be pre-extended to 3/2 source.  Do not use in-place.
 * We optimize for native, for obvious reasons. */

U8*
Perl_utf16_to_utf8(pTHX_ U8* p, U8* d, I32 bytelen, I32 *newlen)
{
    U8* pend;
    U8* dstart = d;

    PERL_ARGS_ASSERT_UTF16_TO_UTF8;

    if (bytelen & 1)
        Perl_croak(aTHX_ "panic: utf16_to_utf8: odd bytelen %"UVuf, (UV)bytelen);

    pend = p + bytelen;

    while (p < pend) {
        UV uv = (p[0] << 8) + p[1]; /* UTF-16BE */
        p += 2;
        if (UNI_IS_INVARIANT(uv)) {
            *d++ = LATIN1_TO_NATIVE((U8) uv);
            continue;
        }
        if (uv <= MAX_UTF8_TWO_BYTE) {
            *d++ = UTF8_TWO_BYTE_HI(UNI_TO_NATIVE(uv));
            *d++ = UTF8_TWO_BYTE_LO(UNI_TO_NATIVE(uv));
            continue;
        }
#define FIRST_HIGH_SURROGATE UNICODE_SURROGATE_FIRST
#define LAST_HIGH_SURROGATE  0xDBFF
#define FIRST_LOW_SURROGATE  0xDC00
#define LAST_LOW_SURROGATE   UNICODE_SURROGATE_LAST
        if (uv >= FIRST_HIGH_SURROGATE && uv <= LAST_HIGH_SURROGATE) {
            if (p >= pend) {
                Perl_croak(aTHX_ "Malformed UTF-16 surrogate");
            } else {
                UV low = (p[0] << 8) + p[1];
                p += 2;
                if (low < FIRST_LOW_SURROGATE || low > LAST_LOW_SURROGATE)
                    Perl_croak(aTHX_ "Malformed UTF-16 surrogate");
                uv = ((uv - FIRST_HIGH_SURROGATE) << 10)
                                       + (low - FIRST_LOW_SURROGATE) + 0x10000;
            }
        } else if (uv >= FIRST_LOW_SURROGATE && uv <= LAST_LOW_SURROGATE) {
            Perl_croak(aTHX_ "Malformed UTF-16 surrogate");
        }
#ifdef EBCDIC
        d = uvoffuni_to_utf8_flags(d, uv, 0);
#else
        if (uv < 0x10000) {
            *d++ = (U8)(( uv >> 12)         | 0xe0);
            *d++ = (U8)(((uv >>  6) & 0x3f) | 0x80);
            *d++ = (U8)(( uv        & 0x3f) | 0x80);
            continue;
        }
        else {
            *d++ = (U8)(( uv >> 18)         | 0xf0);
            *d++ = (U8)(((uv >> 12) & 0x3f) | 0x80);
            *d++ = (U8)(((uv >>  6) & 0x3f) | 0x80);
            *d++ = (U8)(( uv        & 0x3f) | 0x80);
            continue;
        }
#endif
    }
    *newlen = d - dstart;
    return d;
}

/* Note: this one is slightly destructive of the source. */

U8*
Perl_utf16_to_utf8_reversed(pTHX_ U8* p, U8* d, I32 bytelen, I32 *newlen)
{
    U8* s = (U8*)p;
    U8* const send = s + bytelen;

    PERL_ARGS_ASSERT_UTF16_TO_UTF8_REVERSED;

    if (bytelen & 1)
        Perl_croak(aTHX_ "panic: utf16_to_utf8_reversed: odd bytelen %"UVuf,
                   (UV)bytelen);

    while (s < send) {
        const U8 tmp = s[0];
        s[0] = s[1];
        s[1] = tmp;
        s += 2;
    }
    return utf16_to_utf8(p, d, bytelen, newlen);
}

bool
Perl__is_uni_FOO(pTHX_ const U8 classnum, const UV c)
{
    U8 tmpbuf[UTF8_MAXBYTES+1];
    uvchr_to_utf8(tmpbuf, c);
    return _is_utf8_FOO(classnum, tmpbuf);
}

/* Internal function so we can deprecate the external one, and call
   this one from other deprecated functions in this file */

bool
Perl__is_utf8_idstart(pTHX_ const U8 *p)
{
    PERL_ARGS_ASSERT__IS_UTF8_IDSTART;

    if (*p == '_')
        return TRUE;
    return is_utf8_common(p, &PL_utf8_idstart, "IdStart", NULL);
}

bool
Perl__is_uni_perl_idcont(pTHX_ UV c)
{
    U8 tmpbuf[UTF8_MAXBYTES+1];
    uvchr_to_utf8(tmpbuf, c);
    return _is_utf8_perl_idcont(tmpbuf);
}

bool
Perl__is_uni_perl_idstart(pTHX_ UV c)
{
    U8 tmpbuf[UTF8_MAXBYTES+1];
    uvchr_to_utf8(tmpbuf, c);
    return _is_utf8_perl_idstart(tmpbuf);
}

UV
Perl__to_upper_title_latin1(pTHX_ const U8 c, U8* p, STRLEN *lenp, const char S_or_s)
{
    /* We have the latin1-range values compiled into the core, so just use
     * those, converting the result to utf8.  The only difference between upper
     * and title case in this range is that LATIN_SMALL_LETTER_SHARP_S is
     * either "SS" or "Ss".  Which one to use is passed into the routine in
     * 'S_or_s' to avoid a test */

    UV converted = toUPPER_LATIN1_MOD(c);

    PERL_ARGS_ASSERT__TO_UPPER_TITLE_LATIN1;

    assert(S_or_s == 'S' || S_or_s == 's');

    if (UVCHR_IS_INVARIANT(converted)) { /* No difference between the two for
                                             characters in this range */
        *p = (U8) converted;
        *lenp = 1;
        return converted;
    }

    /* toUPPER_LATIN1_MOD gives the correct results except for three outliers,
     * which it maps to one of them, so as to only have to have one check for
     * it in the main case */
    if (UNLIKELY(converted == LATIN_SMALL_LETTER_Y_WITH_DIAERESIS)) {
        switch (c) {
            case LATIN_SMALL_LETTER_Y_WITH_DIAERESIS:
                converted = LATIN_CAPITAL_LETTER_Y_WITH_DIAERESIS;
                break;
            case MICRO_SIGN:
                converted = GREEK_CAPITAL_LETTER_MU;
                break;
            case LATIN_SMALL_LETTER_SHARP_S:
                *(p)++ = 'S';
                *p = S_or_s;
                *lenp = 2;
                return 'S';
            default:
                Perl_croak(aTHX_ "panic: to_upper_title_latin1 did not expect '%c' to map to '%c'", c, LATIN_SMALL_LETTER_Y_WITH_DIAERESIS);
                NOT_REACHED; /* NOTREACHED */
        }
    }

    *(p)++ = UTF8_TWO_BYTE_HI(converted);
    *p = UTF8_TWO_BYTE_LO(converted);
    *lenp = 2;

    return converted;
}

/* Call the function to convert a UTF-8 encoded character to the specified case.
 * Note that there may be more than one character in the result.
 * INP is a pointer to the first byte of the input character
 * OUTP will be set to the first byte of the string of changed characters.  It
 *      needs to have space for UTF8_MAXBYTES_CASE+1 bytes
 * LENP will be set to the length in bytes of the string of changed characters
 *
 * The functions return the ordinal of the first character in the string of OUTP */
#define CALL_UPPER_CASE(INP, OUTP, LENP) Perl_to_utf8_case(aTHX_ INP, OUTP, LENP, &PL_utf8_toupper, "ToUc", "")
#define CALL_TITLE_CASE(INP, OUTP, LENP) Perl_to_utf8_case(aTHX_ INP, OUTP, LENP, &PL_utf8_totitle, "ToTc", "")
#define CALL_LOWER_CASE(INP, OUTP, LENP) Perl_to_utf8_case(aTHX_ INP, OUTP, LENP, &PL_utf8_tolower, "ToLc", "")

/* This additionally has the input parameter SPECIALS, which if non-zero will
 * cause this to use the SPECIALS hash for folding (meaning get full case
 * folding); otherwise, when zero, this implies a simple case fold */
#define CALL_FOLD_CASE(INP, OUTP, LENP, SPECIALS) Perl_to_utf8_case(aTHX_ INP, OUTP, LENP, &PL_utf8_tofold, "ToCf", (SPECIALS) ? "" : NULL)

UV
Perl_to_uni_upper(pTHX_ UV c, U8* p, STRLEN *lenp)
{
    /* Convert the Unicode character whose ordinal is <c> to its uppercase
     * version and store that in UTF-8 in <p> and its length in bytes in <lenp>.
     * Note that the <p> needs to be at least UTF8_MAXBYTES_CASE+1 bytes since
     * the changed version may be longer than the original character.
     *
     * The ordinal of the first character of the changed version is returned
     * (but note, as explained above, that there may be more.) */

    PERL_ARGS_ASSERT_TO_UNI_UPPER;

    if (c < 256) {
        return _to_upper_title_latin1((U8) c, p, lenp, 'S');
    }

    uvchr_to_utf8(p, c);
    return CALL_UPPER_CASE(p, p, lenp);
}

UV
Perl_to_uni_title(pTHX_ UV c, U8* p, STRLEN *lenp)
{
    PERL_ARGS_ASSERT_TO_UNI_TITLE;

    if (c < 256) {
        return _to_upper_title_latin1((U8) c, p, lenp, 's');
    }

    uvchr_to_utf8(p, c);
    return CALL_TITLE_CASE(p, p, lenp);
}

STATIC U8
S_to_lower_latin1(const U8 c, U8* p, STRLEN *lenp)
{
    /* We have the latin1-range values compiled into the core, so just use
     * those, converting the result to utf8.  Since the result is always just
     * one character, we allow <p> to be NULL */

    U8 converted = toLOWER_LATIN1(c);

    if (p != NULL) {
        if (NATIVE_BYTE_IS_INVARIANT(converted)) {
            *p = converted;
            *lenp = 1;
        }
        else {
            /* Result is known to always be < 256, so can use the EIGHT_BIT
             * macros */
            *p = UTF8_EIGHT_BIT_HI(converted);
            *(p+1) = UTF8_EIGHT_BIT_LO(converted);
            *lenp = 2;
        }
    }
    return converted;
}

UV
Perl_to_uni_lower(pTHX_ UV c, U8* p, STRLEN *lenp)
{
    PERL_ARGS_ASSERT_TO_UNI_LOWER;

    if (c < 256) {
        return to_lower_latin1((U8) c, p, lenp);
    }

    uvchr_to_utf8(p, c);
    return CALL_LOWER_CASE(p, p, lenp);
}

UV
Perl__to_fold_latin1(pTHX_ const U8 c, U8* p, STRLEN *lenp, const unsigned int flags)
{
    /* Corresponds to to_lower_latin1(); <flags> bits meanings:
     *      FOLD_FLAGS_NOMIX_ASCII iff non-ASCII to ASCII folds are prohibited
     *      FOLD_FLAGS_FULL  iff full folding is to be used;
     *
     *  Not to be used for locale folds
     */

    UV converted;

    PERL_ARGS_ASSERT__TO_FOLD_LATIN1;
    PERL_UNUSED_CONTEXT;

    assert (! (flags & FOLD_FLAGS_LOCALE));

    if (c == MICRO_SIGN) {
        converted = GREEK_SMALL_LETTER_MU;
    }
    else if ((flags & FOLD_FLAGS_FULL) && c == LATIN_SMALL_LETTER_SHARP_S) {

        /* If can't cross 127/128 boundary, can't return "ss"; instead return
         * two U+017F characters, as fc("\df") should eq fc("\x{17f}\x{17f}")
         * under those circumstances. */
        if (flags & FOLD_FLAGS_NOMIX_ASCII) {
            *lenp = 2 * sizeof(LATIN_SMALL_LETTER_LONG_S_UTF8) - 2;
            Copy(LATIN_SMALL_LETTER_LONG_S_UTF8 LATIN_SMALL_LETTER_LONG_S_UTF8,
                 p, *lenp, U8);
            return LATIN_SMALL_LETTER_LONG_S;
        }
        else {
            *(p)++ = 's';
            *p = 's';
            *lenp = 2;
            return 's';
        }
    }
    else { /* In this range the fold of all other characters is their lower
              case */
        converted = toLOWER_LATIN1(c);
    }

    if (UVCHR_IS_INVARIANT(converted)) {
        *p = (U8) converted;
        *lenp = 1;
    }
    else {
        *(p)++ = UTF8_TWO_BYTE_HI(converted);
        *p = UTF8_TWO_BYTE_LO(converted);
        *lenp = 2;
    }

    return converted;
}

UV
Perl__to_uni_fold_flags(pTHX_ UV c, U8* p, STRLEN *lenp, U8 flags)
{

    /* Not currently externally documented, and subject to change
     *  <flags> bits meanings:
     *      FOLD_FLAGS_FULL  iff full folding is to be used;
     *      FOLD_FLAGS_LOCALE is set iff the rules from the current underlying
     *                        locale are to be used.
     *      FOLD_FLAGS_NOMIX_ASCII iff non-ASCII to ASCII folds are prohibited
     */

    PERL_ARGS_ASSERT__TO_UNI_FOLD_FLAGS;

    if (flags & FOLD_FLAGS_LOCALE) {
        /* Treat a UTF-8 locale as not being in locale at all */
        if (IN_UTF8_CTYPE_LOCALE) {
            flags &= ~FOLD_FLAGS_LOCALE;
        }
        else {
            _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
            goto needs_full_generality;
        }
    }

    if (c < 256) {
        return _to_fold_latin1((U8) c, p, lenp,
                            flags & (FOLD_FLAGS_FULL | FOLD_FLAGS_NOMIX_ASCII));
    }

    /* Here, above 255.  If no special needs, just use the macro */
    if ( ! (flags & (FOLD_FLAGS_LOCALE|FOLD_FLAGS_NOMIX_ASCII))) {
        uvchr_to_utf8(p, c);
        return CALL_FOLD_CASE(p, p, lenp, flags & FOLD_FLAGS_FULL);
    }
    else {  /* Otherwise, _to_utf8_fold_flags has the intelligence to deal with
               the special flags. */
        U8 utf8_c[UTF8_MAXBYTES + 1];

      needs_full_generality:
        uvchr_to_utf8(utf8_c, c);
        return _to_utf8_fold_flags(utf8_c, p, lenp, flags);
    }
}

PERL_STATIC_INLINE bool
S_is_utf8_common(pTHX_ const U8 *const p, SV **swash,
                 const char *const swashname, SV* const invlist)
{
    /* returns a boolean giving whether or not the UTF8-encoded character that
     * starts at <p> is in the swash indicated by <swashname>.  <swash>
     * contains a pointer to where the swash indicated by <swashname>
     * is to be stored; which this routine will do, so that future calls will
     * look at <*swash> and only generate a swash if it is not null.  <invlist>
     * is NULL or an inversion list that defines the swash.  If not null, it
     * saves time during initialization of the swash.
     *
     * Note that it is assumed that the buffer length of <p> is enough to
     * contain all the bytes that comprise the character.  Thus, <*p> should
     * have been checked before this call for mal-formedness enough to assure
     * that. */

    PERL_ARGS_ASSERT_IS_UTF8_COMMON;

    /* The API should have included a length for the UTF-8 character in <p>,
     * but it doesn't.  We therefore assume that p has been validated at least
     * as far as there being enough bytes available in it to accommodate the
     * character without reading beyond the end, and pass that number on to the
     * validating routine */
    if (! isUTF8_CHAR(p, p + UTF8SKIP(p))) {
        if (ckWARN_d(WARN_UTF8)) {
            Perl_warner(aTHX_ packWARN2(WARN_DEPRECATED,WARN_UTF8),
                    "Passing malformed UTF-8 to \"%s\" is deprecated", swashname);
            if (ckWARN(WARN_UTF8)) {    /* This will output details as to the
                                           what the malformation is */
                utf8_to_uvchr_buf(p, p + UTF8SKIP(p), NULL);
            }
        }
        return FALSE;
    }
    if (!*swash) {
        U8 flags = _CORE_SWASH_INIT_ACCEPT_INVLIST;
        *swash = _core_swash_init("utf8",

                                  /* Only use the name if there is no inversion
                                   * list; otherwise will go out to disk */
                                  (invlist) ? "" : swashname,

                                  &PL_sv_undef, 1, 0, invlist, &flags);
    }

    return swash_fetch(*swash, p, TRUE) != 0;
}

bool
Perl__is_utf8_FOO(pTHX_ const U8 classnum, const U8 *p)
{
    PERL_ARGS_ASSERT__IS_UTF8_FOO;

    assert(classnum < _FIRST_NON_SWASH_CC);

    return is_utf8_common(p,
                          &PL_utf8_swash_ptrs[classnum],
                          swash_property_names[classnum],
                          PL_XPosix_ptrs[classnum]);
}

bool
Perl__is_utf8_perl_idstart(pTHX_ const U8 *p)
{
    SV* invlist = NULL;

    PERL_ARGS_ASSERT__IS_UTF8_PERL_IDSTART;

    if (! PL_utf8_perl_idstart) {
        invlist = _new_invlist_C_array(_Perl_IDStart_invlist);
    }
    return is_utf8_common(p, &PL_utf8_perl_idstart, "_Perl_IDStart", invlist);
}

bool
Perl__is_utf8_xidstart(pTHX_ const U8 *p)
{
    PERL_ARGS_ASSERT__IS_UTF8_XIDSTART;

    if (*p == '_')
        return TRUE;
    return is_utf8_common(p, &PL_utf8_xidstart, "XIdStart", NULL);
}

bool
Perl__is_utf8_perl_idcont(pTHX_ const U8 *p)
{
    SV* invlist = NULL;

    PERL_ARGS_ASSERT__IS_UTF8_PERL_IDCONT;

    if (! PL_utf8_perl_idcont) {
        invlist = _new_invlist_C_array(_Perl_IDCont_invlist);
    }
    return is_utf8_common(p, &PL_utf8_perl_idcont, "_Perl_IDCont", invlist);
}

bool
Perl__is_utf8_idcont(pTHX_ const U8 *p)
{
    PERL_ARGS_ASSERT__IS_UTF8_IDCONT;

    return is_utf8_common(p, &PL_utf8_idcont, "IdContinue", NULL);
}

bool
Perl__is_utf8_xidcont(pTHX_ const U8 *p)
{
    PERL_ARGS_ASSERT__IS_UTF8_XIDCONT;

    return is_utf8_common(p, &PL_utf8_idcont, "XIdContinue", NULL);
}

bool
Perl__is_utf8_mark(pTHX_ const U8 *p)
{
    PERL_ARGS_ASSERT__IS_UTF8_MARK;

    return is_utf8_common(p, &PL_utf8_mark, "IsM", NULL);
}

/*
=for apidoc to_utf8_case

C<p> contains the pointer to the UTF-8 string encoding
the character that is being converted.  This routine assumes that the character
at C<p> is well-formed.

C<ustrp> is a pointer to the character buffer to put the
conversion result to.  C<lenp> is a pointer to the length
of the result.

C<swashp> is a pointer to the swash to use.

Both the special and normal mappings are stored in F<lib/unicore/To/Foo.pl>,
and loaded by SWASHNEW, using F<lib/utf8_heavy.pl>.  C<special> (usually,
but not always, a multicharacter mapping), is tried first.

C<special> is a string, normally C<NULL> or C<"">.  C<NULL> means to not use
any special mappings; C<""> means to use the special mappings.  Values other
than these two are treated as the name of the hash containing the special
mappings, like C<"utf8::ToSpecLower">.

C<normal> is a string like "ToLower" which means the swash
%utf8::ToLower.

=cut */

UV
Perl_to_utf8_case(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp,
                        SV **swashp, const char *normal, const char *special)
{
    STRLEN len = 0;
    const UV uv1 = valid_utf8_to_uvchr(p, NULL);

    PERL_ARGS_ASSERT_TO_UTF8_CASE;

    /* Note that swash_fetch() doesn't output warnings for these because it
     * assumes we will */
    if (uv1 >= UNICODE_SURROGATE_FIRST) {
        if (uv1 <= UNICODE_SURROGATE_LAST) {
            if (ckWARN_d(WARN_SURROGATE)) {
                const char* desc = (PL_op) ? OP_DESC(PL_op) : normal;
                Perl_warner(aTHX_ packWARN(WARN_SURROGATE),
                    "Operation \"%s\" returns its argument for UTF-16 surrogate U+%04"UVXf"", desc, uv1);
            }
        }
        else if (UNICODE_IS_SUPER(uv1)) {
            if (ckWARN_d(WARN_NON_UNICODE)) {
                const char* desc = (PL_op) ? OP_DESC(PL_op) : normal;
                Perl_warner(aTHX_ packWARN(WARN_NON_UNICODE),
                    "Operation \"%s\" returns its argument for non-Unicode code point 0x%04"UVXf"", desc, uv1);
            }
        }

        /* Note that non-characters are perfectly legal, so no warning should
         * be given */
    }

    if (!*swashp) /* load on-demand */
         *swashp = _core_swash_init("utf8", normal, &PL_sv_undef, 4, 0, NULL, NULL);

    if (special) {
         /* It might be "special" (sometimes, but not always,
          * a multicharacter mapping) */
         HV *hv = NULL;
         SV **svp;

         /* If passed in the specials name, use that; otherwise use any
          * given in the swash */
         if (*special != '\0') {
            hv = get_hv(special, 0);
        }
        else {
            svp = hv_fetchs(MUTABLE_HV(SvRV(*swashp)), "SPECIALS", 0);
            if (svp) {
                hv = MUTABLE_HV(SvRV(*svp));
            }
        }

         if (hv
             && (svp = hv_fetch(hv, (const char*)p, UNISKIP(uv1), FALSE))
             && (*svp))
         {
             const char *s;

              s = SvPV_const(*svp, len);
              if (len == 1)
                  /* EIGHTBIT */
                   len = uvchr_to_utf8(ustrp, *(U8*)s) - ustrp;
              else {
                   Copy(s, ustrp, len, U8);
              }
         }
    }

    if (!len && *swashp) {
        const UV uv2 = swash_fetch(*swashp, p, TRUE /* => is utf8 */);

         if (uv2) {
              /* It was "normal" (a single character mapping). */
              len = uvchr_to_utf8(ustrp, uv2) - ustrp;
         }
    }

    if (len) {
        if (lenp) {
            *lenp = len;
        }
        return valid_utf8_to_uvchr(ustrp, 0);
    }

    /* Here, there was no mapping defined, which means that the code point maps
     * to itself.  Return the inputs */
    len = UTF8SKIP(p);
    if (p != ustrp) {   /* Don't copy onto itself */
        Copy(p, ustrp, len, U8);
    }

    if (lenp)
         *lenp = len;

    return uv1;

}

STATIC UV
S_check_locale_boundary_crossing(pTHX_ const U8* const p, const UV result, U8* const ustrp, STRLEN *lenp)
{
    /* This is called when changing the case of a utf8-encoded character above
     * the Latin1 range, and the operation is in a non-UTF-8 locale.  If the
     * result contains a character that crosses the 255/256 boundary, disallow
     * the change, and return the original code point.  See L<perlfunc/lc> for
     * why;
     *
     * p        points to the original string whose case was changed; assumed
     *          by this routine to be well-formed
     * result   the code point of the first character in the changed-case string
     * ustrp    points to the changed-case string (<result> represents its first char)
     * lenp     points to the length of <ustrp> */

    UV original;    /* To store the first code point of <p> */

    PERL_ARGS_ASSERT_CHECK_LOCALE_BOUNDARY_CROSSING;

    assert(UTF8_IS_ABOVE_LATIN1(*p));

    /* We know immediately if the first character in the string crosses the
     * boundary, so can skip */
    if (result > 255) {

        /* Look at every character in the result; if any cross the
        * boundary, the whole thing is disallowed */
        U8* s = ustrp + UTF8SKIP(ustrp);
        U8* e = ustrp + *lenp;
        while (s < e) {
            if (! UTF8_IS_ABOVE_LATIN1(*s)) {
                goto bad_crossing;
            }
            s += UTF8SKIP(s);
        }

        /* Here, no characters crossed, result is ok as-is, but we warn. */
        _CHECK_AND_OUTPUT_WIDE_LOCALE_UTF8_MSG(p, p + UTF8SKIP(p));
        return result;
    }

  bad_crossing:

    /* Failed, have to return the original */
    original = valid_utf8_to_uvchr(p, lenp);

    /* diag_listed_as: Can't do %s("%s") on non-UTF-8 locale; resolved to "%s". */
    Perl_ck_warner(aTHX_ packWARN(WARN_LOCALE),
                           "Can't do %s(\"\\x{%"UVXf"}\") on non-UTF-8 locale; "
                           "resolved to \"\\x{%"UVXf"}\".",
                           OP_DESC(PL_op),
                           original,
                           original);
    Copy(p, ustrp, *lenp, char);
    return original;
}

/*
=for apidoc to_utf8_upper

Instead use L</toUPPER_utf8>.

=cut */

/* Not currently externally documented, and subject to change:
 * <flags> is set iff iff the rules from the current underlying locale are to
 *         be used. */

UV
Perl__to_utf8_upper_flags(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp, bool flags)
{
    UV result;

    PERL_ARGS_ASSERT__TO_UTF8_UPPER_FLAGS;

    if (flags) {
        /* Treat a UTF-8 locale as not being in locale at all */
        if (IN_UTF8_CTYPE_LOCALE) {
            flags = FALSE;
        }
        else {
            _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        }
    }

    if (UTF8_IS_INVARIANT(*p)) {
        if (flags) {
            result = toUPPER_LC(*p);
        }
        else {
            return _to_upper_title_latin1(*p, ustrp, lenp, 'S');
        }
    }
    else if UTF8_IS_DOWNGRADEABLE_START(*p) {
        if (flags) {
            U8 c = TWO_BYTE_UTF8_TO_NATIVE(*p, *(p+1));
            result = toUPPER_LC(c);
        }
        else {
            return _to_upper_title_latin1(TWO_BYTE_UTF8_TO_NATIVE(*p, *(p+1)),
                                          ustrp, lenp, 'S');
        }
    }
    else {  /* utf8, ord above 255 */
        result = CALL_UPPER_CASE(p, ustrp, lenp);

        if (flags) {
            result = check_locale_boundary_crossing(p, result, ustrp, lenp);
        }
        return result;
    }

    /* Here, used locale rules.  Convert back to utf8 */
    if (UTF8_IS_INVARIANT(result)) {
        *ustrp = (U8) result;
        *lenp = 1;
    }
    else {
        *ustrp = UTF8_EIGHT_BIT_HI((U8) result);
        *(ustrp + 1) = UTF8_EIGHT_BIT_LO((U8) result);
        *lenp = 2;
    }

    return result;
}

/*
=for apidoc to_utf8_title

Instead use L</toTITLE_utf8>.

=cut */

/* Not currently externally documented, and subject to change:
 * <flags> is set iff the rules from the current underlying locale are to be
 *         used.  Since titlecase is not defined in POSIX, for other than a
 *         UTF-8 locale, uppercase is used instead for code points < 256.
 */

UV
Perl__to_utf8_title_flags(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp, bool flags)
{
    UV result;

    PERL_ARGS_ASSERT__TO_UTF8_TITLE_FLAGS;

    if (flags) {
        /* Treat a UTF-8 locale as not being in locale at all */
        if (IN_UTF8_CTYPE_LOCALE) {
            flags = FALSE;
        }
        else {
            _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        }
    }

    if (UTF8_IS_INVARIANT(*p)) {
        if (flags) {
            result = toUPPER_LC(*p);
        }
        else {
            return _to_upper_title_latin1(*p, ustrp, lenp, 's');
        }
    }
    else if UTF8_IS_DOWNGRADEABLE_START(*p) {
        if (flags) {
            U8 c = TWO_BYTE_UTF8_TO_NATIVE(*p, *(p+1));
            result = toUPPER_LC(c);
        }
        else {
            return _to_upper_title_latin1(TWO_BYTE_UTF8_TO_NATIVE(*p, *(p+1)),
                                          ustrp, lenp, 's');
        }
    }
    else {  /* utf8, ord above 255 */
        result = CALL_TITLE_CASE(p, ustrp, lenp);

        if (flags) {
            result = check_locale_boundary_crossing(p, result, ustrp, lenp);
        }
        return result;
    }

    /* Here, used locale rules.  Convert back to utf8 */
    if (UTF8_IS_INVARIANT(result)) {
        *ustrp = (U8) result;
        *lenp = 1;
    }
    else {
        *ustrp = UTF8_EIGHT_BIT_HI((U8) result);
        *(ustrp + 1) = UTF8_EIGHT_BIT_LO((U8) result);
        *lenp = 2;
    }

    return result;
}

/*
=for apidoc to_utf8_lower

Instead use L</toLOWER_utf8>.

=cut */

/* Not currently externally documented, and subject to change:
 * <flags> is set iff iff the rules from the current underlying locale are to
 *         be used.
 */

UV
Perl__to_utf8_lower_flags(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp, bool flags)
{
    UV result;

    PERL_ARGS_ASSERT__TO_UTF8_LOWER_FLAGS;

    if (flags) {
        /* Treat a UTF-8 locale as not being in locale at all */
        if (IN_UTF8_CTYPE_LOCALE) {
            flags = FALSE;
        }
        else {
            _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        }
    }

    if (UTF8_IS_INVARIANT(*p)) {
        if (flags) {
            result = toLOWER_LC(*p);
        }
        else {
            return to_lower_latin1(*p, ustrp, lenp);
        }
    }
    else if UTF8_IS_DOWNGRADEABLE_START(*p) {
        if (flags) {
            U8 c = TWO_BYTE_UTF8_TO_NATIVE(*p, *(p+1));
            result = toLOWER_LC(c);
        }
        else {
            return to_lower_latin1(TWO_BYTE_UTF8_TO_NATIVE(*p, *(p+1)),
                                   ustrp, lenp);
        }
    }
    else {  /* utf8, ord above 255 */
        result = CALL_LOWER_CASE(p, ustrp, lenp);

        if (flags) {
            result = check_locale_boundary_crossing(p, result, ustrp, lenp);
        }

        return result;
    }

    /* Here, used locale rules.  Convert back to utf8 */
    if (UTF8_IS_INVARIANT(result)) {
        *ustrp = (U8) result;
        *lenp = 1;
    }
    else {
        *ustrp = UTF8_EIGHT_BIT_HI((U8) result);
        *(ustrp + 1) = UTF8_EIGHT_BIT_LO((U8) result);
        *lenp = 2;
    }

    return result;
}

/*
=for apidoc to_utf8_fold

Instead use L</toFOLD_utf8>.

=cut */

/* Not currently externally documented, and subject to change,
 * in <flags>
 *      bit FOLD_FLAGS_LOCALE is set iff the rules from the current underlying
 *                            locale are to be used.
 *      bit FOLD_FLAGS_FULL   is set iff full case folds are to be used;
 *                            otherwise simple folds
 *      bit FOLD_FLAGS_NOMIX_ASCII is set iff folds of non-ASCII to ASCII are
 *                            prohibited
 */

UV
Perl__to_utf8_fold_flags(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp, U8 flags)
{
    UV result;

    PERL_ARGS_ASSERT__TO_UTF8_FOLD_FLAGS;

    /* These are mutually exclusive */
    assert (! ((flags & FOLD_FLAGS_LOCALE) && (flags & FOLD_FLAGS_NOMIX_ASCII)));

    assert(p != ustrp); /* Otherwise overwrites */

    if (flags & FOLD_FLAGS_LOCALE) {
        /* Treat a UTF-8 locale as not being in locale at all */
        if (IN_UTF8_CTYPE_LOCALE) {
            flags &= ~FOLD_FLAGS_LOCALE;
        }
        else {
            _CHECK_AND_WARN_PROBLEMATIC_LOCALE;
        }
    }

    if (UTF8_IS_INVARIANT(*p)) {
        if (flags & FOLD_FLAGS_LOCALE) {
            result = toFOLD_LC(*p);
        }
        else {
            return _to_fold_latin1(*p, ustrp, lenp,
                            flags & (FOLD_FLAGS_FULL | FOLD_FLAGS_NOMIX_ASCII));
        }
    }
    else if UTF8_IS_DOWNGRADEABLE_START(*p) {
        if (flags & FOLD_FLAGS_LOCALE) {
            U8 c = TWO_BYTE_UTF8_TO_NATIVE(*p, *(p+1));
            result = toFOLD_LC(c);
        }
        else {
            return _to_fold_latin1(TWO_BYTE_UTF8_TO_NATIVE(*p, *(p+1)),
                            ustrp, lenp,
                            flags & (FOLD_FLAGS_FULL | FOLD_FLAGS_NOMIX_ASCII));
        }
    }
    else {  /* utf8, ord above 255 */
        result = CALL_FOLD_CASE(p, ustrp, lenp, flags & FOLD_FLAGS_FULL);

        if (flags & FOLD_FLAGS_LOCALE) {

#           define CAP_SHARP_S   LATIN_CAPITAL_LETTER_SHARP_S_UTF8
#           define LONG_S_T      LATIN_SMALL_LIGATURE_LONG_S_T_UTF8

            const unsigned int cap_sharp_s_len = sizeof(CAP_SHARP_S) - 1;
            const unsigned int long_s_t_len    = sizeof(LONG_S_T) - 1;

            /* Special case these two characters, as what normally gets
             * returned under locale doesn't work */
            if (UTF8SKIP(p) == cap_sharp_s_len
                && memEQ((char *) p, CAP_SHARP_S, cap_sharp_s_len))
            {
                /* diag_listed_as: Can't do %s("%s") on non-UTF-8 locale; resolved to "%s". */
                Perl_ck_warner(aTHX_ packWARN(WARN_LOCALE),
                              "Can't do fc(\"\\x{1E9E}\") on non-UTF-8 locale; "
                              "resolved to \"\\x{17F}\\x{17F}\".");
                goto return_long_s;
            }
            else if (UTF8SKIP(p) == long_s_t_len
                     && memEQ((char *) p, LONG_S_T, long_s_t_len))
            {
                /* diag_listed_as: Can't do %s("%s") on non-UTF-8 locale; resolved to "%s". */
                Perl_ck_warner(aTHX_ packWARN(WARN_LOCALE),
                              "Can't do fc(\"\\x{FB05}\") on non-UTF-8 locale; "
                              "resolved to \"\\x{FB06}\".");
                goto return_ligature_st;
            }
            return check_locale_boundary_crossing(p, result, ustrp, lenp);
        }
        else if (! (flags & FOLD_FLAGS_NOMIX_ASCII)) {
            return result;
        }
        else {
            /* This is called when changing the case of a utf8-encoded
             * character above the ASCII range, and the result should not
             * contain an ASCII character. */

            UV original;    /* To store the first code point of <p> */

            /* Look at every character in the result; if any cross the
            * boundary, the whole thing is disallowed */
            U8* s = ustrp;
            U8* e = ustrp + *lenp;
            while (s < e) {
                if (isASCII(*s)) {
                    /* Crossed, have to return the original */
                    original = valid_utf8_to_uvchr(p, lenp);

                    /* But in these instances, there is an alternative we can
                     * return that is valid */
                    if (original == LATIN_CAPITAL_LETTER_SHARP_S
                        || original == LATIN_SMALL_LETTER_SHARP_S)
                    {
                        goto return_long_s;
                    }
                    else if (original == LATIN_SMALL_LIGATURE_LONG_S_T) {
                        goto return_ligature_st;
                    }
                    Copy(p, ustrp, *lenp, char);
                    return original;
                }
                s += UTF8SKIP(s);
            }

            /* Here, no characters crossed, result is ok as-is */
            return result;
        }
    }

    /* Here, used locale rules.  Convert back to utf8 */
    if (UTF8_IS_INVARIANT(result)) {
        *ustrp = (U8) result;
        *lenp = 1;
    }
    else {
        *ustrp = UTF8_EIGHT_BIT_HI((U8) result);
        *(ustrp + 1) = UTF8_EIGHT_BIT_LO((U8) result);
        *lenp = 2;
    }

    return result;

  return_long_s:
    /* Certain folds to 'ss' are prohibited by the options, but they do allow
     * folds to a string of two of these characters.  By returning this
     * instead, then, e.g.,
     *      fc("\x{1E9E}") eq fc("\x{17F}\x{17F}")
     * works. */

    *lenp = 2 * sizeof(LATIN_SMALL_LETTER_LONG_S_UTF8) - 2;
    Copy(LATIN_SMALL_LETTER_LONG_S_UTF8 LATIN_SMALL_LETTER_LONG_S_UTF8,
        ustrp, *lenp, U8);
    return LATIN_SMALL_LETTER_LONG_S;

  return_ligature_st:
    /* Two folds to 'st' are prohibited by the options; instead we pick one and
     * have the other one fold to it */

    *lenp = sizeof(LATIN_SMALL_LIGATURE_ST_UTF8) - 1;
    Copy(LATIN_SMALL_LIGATURE_ST_UTF8, ustrp, *lenp, U8);
    return LATIN_SMALL_LIGATURE_ST;
}

/* Note:
 * Returns a "swash" which is a hash described in utf8.c:Perl_swash_fetch().
 * C<pkg> is a pointer to a package name for SWASHNEW, should be "utf8".
 * For other parameters, see utf8::SWASHNEW in lib/utf8_heavy.pl.
 */

SV*
Perl_swash_init(pTHX_ const char* pkg, const char* name, SV *listsv, I32 minbits, I32 none)
{
    PERL_ARGS_ASSERT_SWASH_INIT;

    /* Returns a copy of a swash initiated by the called function.  This is the
     * public interface, and returning a copy prevents others from doing
     * mischief on the original */

    return newSVsv(_core_swash_init(pkg, name, listsv, minbits, none, NULL, NULL));
}

SV*
Perl__core_swash_init(pTHX_ const char* pkg, const char* name, SV *listsv, I32 minbits, I32 none, SV* invlist, U8* const flags_p)
{

    /*NOTE NOTE NOTE - If you want to use "return" in this routine you MUST
     * use the following define */

#define CORE_SWASH_INIT_RETURN(x)   \
    PL_curpm= old_PL_curpm;         \
    return x

    /* Initialize and return a swash, creating it if necessary.  It does this
     * by calling utf8_heavy.pl in the general case.  The returned value may be
     * the swash's inversion list instead if the input parameters allow it.
     * Which is returned should be immaterial to callers, as the only
     * operations permitted on a swash, swash_fetch(), _get_swash_invlist(),
     * and swash_to_invlist() handle both these transparently.
     *
     * This interface should only be used by functions that won't destroy or
     * adversely change the swash, as doing so affects all other uses of the
     * swash in the program; the general public should use 'Perl_swash_init'
     * instead.
     *
     * pkg  is the name of the package that <name> should be in.
     * name is the name of the swash to find.  Typically it is a Unicode
     *      property name, including user-defined ones
     * listsv is a string to initialize the swash with.  It must be of the form
     *      documented as the subroutine return value in
     *      L<perlunicode/User-Defined Character Properties>
     * minbits is the number of bits required to represent each data element.
     *      It is '1' for binary properties.
     * none I (khw) do not understand this one, but it is used only in tr///.
     * invlist is an inversion list to initialize the swash with (or NULL)
     * flags_p if non-NULL is the address of various input and output flag bits
     *      to the routine, as follows:  ('I' means is input to the routine;
     *      'O' means output from the routine.  Only flags marked O are
     *      meaningful on return.)
     *  _CORE_SWASH_INIT_USER_DEFINED_PROPERTY indicates if the swash
     *      came from a user-defined property.  (I O)
     *  _CORE_SWASH_INIT_RETURN_IF_UNDEF indicates that instead of croaking
     *      when the swash cannot be located, to simply return NULL. (I)
     *  _CORE_SWASH_INIT_ACCEPT_INVLIST indicates that the caller will accept a
     *      return of an inversion list instead of a swash hash if this routine
     *      thinks that would result in faster execution of swash_fetch() later
     *      on. (I)
     *
     * Thus there are three possible inputs to find the swash: <name>,
     * <listsv>, and <invlist>.  At least one must be specified.  The result
     * will be the union of the specified ones, although <listsv>'s various
     * actions can intersect, etc. what <name> gives.  To avoid going out to
     * disk at all, <invlist> should specify completely what the swash should
     * have, and <listsv> should be &PL_sv_undef and <name> should be "".
     *
     * <invlist> is only valid for binary properties */

    PMOP *old_PL_curpm= PL_curpm; /* save away the old PL_curpm */

    SV* retval = &PL_sv_undef;
    HV* swash_hv = NULL;
    const int invlist_swash_boundary =
        (flags_p && *flags_p & _CORE_SWASH_INIT_ACCEPT_INVLIST)
        ? 512    /* Based on some benchmarking, but not extensive, see commit
                    message */
        : -1;   /* Never return just an inversion list */

    assert(listsv != &PL_sv_undef || strNE(name, "") || invlist);
    assert(! invlist || minbits == 1);

    PL_curpm= NULL; /* reset PL_curpm so that we dont get confused between the regex
                       that triggered the swash init and the swash init perl logic itself.
                       See perl #122747 */

    /* If data was passed in to go out to utf8_heavy to find the swash of, do
     * so */
    if (listsv != &PL_sv_undef || strNE(name, "")) {
        dSP;
        const size_t pkg_len = strlen(pkg);
        const size_t name_len = strlen(name);
        HV * const stash = gv_stashpvn(pkg, pkg_len, 0);
        SV* errsv_save;
        GV *method;

        PERL_ARGS_ASSERT__CORE_SWASH_INIT;

        PUSHSTACKi(PERLSI_MAGIC);
        ENTER;
        SAVEHINTS();
        /* We might get here via a subroutine signature which uses a utf8
         * parameter name, at which point PL_subname will have been set
         * but not yet used. */
        save_item(PL_subname);
        if (PL_parser && PL_parser->error_count)
            SAVEI8(PL_parser->error_count), PL_parser->error_count = 0;
        method = gv_fetchmeth(stash, "SWASHNEW", 8, -1);
        if (!method) {  /* demand load utf8 */
            ENTER;
            if ((errsv_save = GvSV(PL_errgv))) SAVEFREESV(errsv_save);
            GvSV(PL_errgv) = NULL;
#ifndef NO_TAINT_SUPPORT
            /* It is assumed that callers of this routine are not passing in
             * any user derived data.  */
            SAVEBOOL(TAINT_get);
            TAINT_NOT;
#endif
            Perl_load_module(aTHX_ PERL_LOADMOD_NOIMPORT, newSVpvn(pkg,pkg_len),
                             NULL);
            {
                /* Not ERRSV, as there is no need to vivify a scalar we are
                   about to discard. */
                SV * const errsv = GvSV(PL_errgv);
                if (!SvTRUE(errsv)) {
                    GvSV(PL_errgv) = SvREFCNT_inc_simple(errsv_save);
                    SvREFCNT_dec(errsv);
                }
            }
            LEAVE;
        }
        SPAGAIN;
        PUSHMARK(SP);
        EXTEND(SP,5);
        mPUSHp(pkg, pkg_len);
        mPUSHp(name, name_len);
        PUSHs(listsv);
        mPUSHi(minbits);
        mPUSHi(none);
        PUTBACK;
        if ((errsv_save = GvSV(PL_errgv))) SAVEFREESV(errsv_save);
        GvSV(PL_errgv) = NULL;
        /* If we already have a pointer to the method, no need to use
         * call_method() to repeat the lookup.  */
        if (method
            ? call_sv(MUTABLE_SV(method), G_SCALAR)
            : call_sv(newSVpvs_flags("SWASHNEW", SVs_TEMP), G_SCALAR | G_METHOD))
        {
            retval = *PL_stack_sp--;
            SvREFCNT_inc(retval);
        }
        {
            /* Not ERRSV.  See above. */
            SV * const errsv = GvSV(PL_errgv);
            if (!SvTRUE(errsv)) {
                GvSV(PL_errgv) = SvREFCNT_inc_simple(errsv_save);
                SvREFCNT_dec(errsv);
            }
        }
        LEAVE;
        POPSTACK;
        if (IN_PERL_COMPILETIME) {
            CopHINTS_set(PL_curcop, PL_hints);
        }
        if (!SvROK(retval) || SvTYPE(SvRV(retval)) != SVt_PVHV) {
            if (SvPOK(retval))

                /* If caller wants to handle missing properties, let them */
                if (flags_p && *flags_p & _CORE_SWASH_INIT_RETURN_IF_UNDEF) {
                    CORE_SWASH_INIT_RETURN(NULL);
                }
                Perl_croak(aTHX_
                           "Can't find Unicode property definition \"%"SVf"\"",
                           SVfARG(retval));
                NOT_REACHED; /* NOTREACHED */
        }
    } /* End of calling the module to find the swash */

    /* If this operation fetched a swash, and we will need it later, get it */
    if (retval != &PL_sv_undef
        && (minbits == 1 || (flags_p
                            && ! (*flags_p
                                  & _CORE_SWASH_INIT_USER_DEFINED_PROPERTY))))
    {
        swash_hv = MUTABLE_HV(SvRV(retval));

        /* If we don't already know that there is a user-defined component to
         * this swash, and the user has indicated they wish to know if there is
         * one (by passing <flags_p>), find out */
        if (flags_p && ! (*flags_p & _CORE_SWASH_INIT_USER_DEFINED_PROPERTY)) {
            SV** user_defined = hv_fetchs(swash_hv, "USER_DEFINED", FALSE);
            if (user_defined && SvUV(*user_defined)) {
                *flags_p |= _CORE_SWASH_INIT_USER_DEFINED_PROPERTY;
            }
        }
    }

    /* Make sure there is an inversion list for binary properties */
    if (minbits == 1) {
        SV** swash_invlistsvp = NULL;
        SV* swash_invlist = NULL;
        bool invlist_in_swash_is_valid = FALSE;
        bool swash_invlist_unclaimed = FALSE; /* whether swash_invlist has
                                            an unclaimed reference count */

        /* If this operation fetched a swash, get its already existing
         * inversion list, or create one for it */

        if (swash_hv) {
            swash_invlistsvp = hv_fetchs(swash_hv, "V", FALSE);
            if (swash_invlistsvp) {
                swash_invlist = *swash_invlistsvp;
                invlist_in_swash_is_valid = TRUE;
            }
            else {
                swash_invlist = _swash_to_invlist(retval);
                swash_invlist_unclaimed = TRUE;
            }
        }

        /* If an inversion list was passed in, have to include it */
        if (invlist) {

            /* Any fetched swash will by now have an inversion list in it;
             * otherwise <swash_invlist>  will be NULL, indicating that we
             * didn't fetch a swash */
            if (swash_invlist) {

                /* Add the passed-in inversion list, which invalidates the one
                 * already stored in the swash */
                invlist_in_swash_is_valid = FALSE;
                _invlist_union(invlist, swash_invlist, &swash_invlist);
            }
            else {

                /* Here, there is no swash already.  Set up a minimal one, if
                 * we are going to return a swash */
                if ((int) _invlist_len(invlist) > invlist_swash_boundary) {
                    swash_hv = newHV();
                    retval = newRV_noinc(MUTABLE_SV(swash_hv));
                }
                swash_invlist = invlist;
            }
        }

        /* Here, we have computed the union of all the passed-in data.  It may
         * be that there was an inversion list in the swash which didn't get
         * touched; otherwise save the computed one */
        if (! invlist_in_swash_is_valid
            && (int) _invlist_len(swash_invlist) > invlist_swash_boundary)
        {
            if (! hv_stores(MUTABLE_HV(SvRV(retval)), "V", swash_invlist))
            {
                Perl_croak(aTHX_ "panic: hv_store() unexpectedly failed");
            }
            /* We just stole a reference count. */
            if (swash_invlist_unclaimed) swash_invlist_unclaimed = FALSE;
            else SvREFCNT_inc_simple_void_NN(swash_invlist);
        }

        SvREADONLY_on(swash_invlist);

        /* Use the inversion list stand-alone if small enough */
        if ((int) _invlist_len(swash_invlist) <= invlist_swash_boundary) {
            SvREFCNT_dec(retval);
            if (!swash_invlist_unclaimed)
                SvREFCNT_inc_simple_void_NN(swash_invlist);
            retval = newRV_noinc(swash_invlist);
        }
    }

    CORE_SWASH_INIT_RETURN(retval);
#undef CORE_SWASH_INIT_RETURN
}


/* This API is wrong for special case conversions since we may need to
 * return several Unicode characters for a single Unicode character
 * (see lib/unicore/SpecCase.txt) The SWASHGET in lib/utf8_heavy.pl is
 * the lower-level routine, and it is similarly broken for returning
 * multiple values.  --jhi
 * For those, you should use to_utf8_case() instead */
/* Now SWASHGET is recasted into S_swatch_get in this file. */

/* Note:
 * Returns the value of property/mapping C<swash> for the first character
 * of the string C<ptr>. If C<do_utf8> is true, the string C<ptr> is
 * assumed to be in well-formed utf8. If C<do_utf8> is false, the string C<ptr>
 * is assumed to be in native 8-bit encoding. Caches the swatch in C<swash>.
 *
 * A "swash" is a hash which contains initially the keys/values set up by
 * SWASHNEW.  The purpose is to be able to completely represent a Unicode
 * property for all possible code points.  Things are stored in a compact form
 * (see utf8_heavy.pl) so that calculation is required to find the actual
 * property value for a given code point.  As code points are looked up, new
 * key/value pairs are added to the hash, so that the calculation doesn't have
 * to ever be re-done.  Further, each calculation is done, not just for the
 * desired one, but for a whole block of code points adjacent to that one.
 * For binary properties on ASCII machines, the block is usually for 64 code
 * points, starting with a code point evenly divisible by 64.  Thus if the
 * property value for code point 257 is requested, the code goes out and
 * calculates the property values for all 64 code points between 256 and 319,
 * and stores these as a single 64-bit long bit vector, called a "swatch",
 * under the key for code point 256.  The key is the UTF-8 encoding for code
 * point 256, minus the final byte.  Thus, if the length of the UTF-8 encoding
 * for a code point is 13 bytes, the key will be 12 bytes long.  If the value
 * for code point 258 is then requested, this code realizes that it would be
 * stored under the key for 256, and would find that value and extract the
 * relevant bit, offset from 256.
 *
 * Non-binary properties are stored in as many bits as necessary to represent
 * their values (32 currently, though the code is more general than that), not
 * as single bits, but the principal is the same: the value for each key is a
 * vector that encompasses the property values for all code points whose UTF-8
 * representations are represented by the key.  That is, for all code points
 * whose UTF-8 representations are length N bytes, and the key is the first N-1
 * bytes of that.
 */
UV
Perl_swash_fetch(pTHX_ SV *swash, const U8 *ptr, bool do_utf8)
{
    HV *const hv = MUTABLE_HV(SvRV(swash));
    U32 klen;
    U32 off;
    STRLEN slen = 0;
    STRLEN needents;
    const U8 *tmps = NULL;
    SV *swatch;
    const U8 c = *ptr;

    PERL_ARGS_ASSERT_SWASH_FETCH;

    /* If it really isn't a hash, it isn't really swash; must be an inversion
     * list */
    if (SvTYPE(hv) != SVt_PVHV) {
        return _invlist_contains_cp((SV*)hv,
                                    (do_utf8)
                                     ? valid_utf8_to_uvchr(ptr, NULL)
                                     : c);
    }

    /* We store the values in a "swatch" which is a vec() value in a swash
     * hash.  Code points 0-255 are a single vec() stored with key length
     * (klen) 0.  All other code points have a UTF-8 representation
     * 0xAA..0xYY,0xZZ.  A vec() is constructed containing all of them which
     * share 0xAA..0xYY, which is the key in the hash to that vec.  So the key
     * length for them is the length of the encoded char - 1.  ptr[klen] is the
     * final byte in the sequence representing the character */
    if (!do_utf8 || UTF8_IS_INVARIANT(c)) {
        klen = 0;
        needents = 256;
        off = c;
    }
    else if (UTF8_IS_DOWNGRADEABLE_START(c)) {
        klen = 0;
        needents = 256;
        off = TWO_BYTE_UTF8_TO_NATIVE(c, *(ptr + 1));
    }
    else {
        klen = UTF8SKIP(ptr) - 1;

        /* Each vec() stores 2**UTF_ACCUMULATION_SHIFT values.  The offset into
         * the vec is the final byte in the sequence.  (In EBCDIC this is
         * converted to I8 to get consecutive values.)  To help you visualize
         * all this:
         *                       Straight 1047   After final byte
         *             UTF-8      UTF-EBCDIC     I8 transform
         *  U+0400:  \xD0\x80    \xB8\x41\x41    \xB8\x41\xA0
         *  U+0401:  \xD0\x81    \xB8\x41\x42    \xB8\x41\xA1
         *    ...
         *  U+0409:  \xD0\x89    \xB8\x41\x4A    \xB8\x41\xA9
         *  U+040A:  \xD0\x8A    \xB8\x41\x51    \xB8\x41\xAA
         *    ...
         *  U+0412:  \xD0\x92    \xB8\x41\x59    \xB8\x41\xB2
         *  U+0413:  \xD0\x93    \xB8\x41\x62    \xB8\x41\xB3
         *    ...
         *  U+041B:  \xD0\x9B    \xB8\x41\x6A    \xB8\x41\xBB
         *  U+041C:  \xD0\x9C    \xB8\x41\x70    \xB8\x41\xBC
         *    ...
         *  U+041F:  \xD0\x9F    \xB8\x41\x73    \xB8\x41\xBF
         *  U+0420:  \xD0\xA0    \xB8\x42\x41    \xB8\x42\x41
         *
         * (There are no discontinuities in the elided (...) entries.)
         * The UTF-8 key for these 33 code points is '\xD0' (which also is the
         * key for the next 31, up through U+043F, whose UTF-8 final byte is
         * \xBF).  Thus in UTF-8, each key is for a vec() for 64 code points.
         * The final UTF-8 byte, which ranges between \x80 and \xBF, is an
         * index into the vec() swatch (after subtracting 0x80, which we
         * actually do with an '&').
         * In UTF-EBCDIC, each key is for a 32 code point vec().  The first 32
         * code points above have key '\xB8\x41'. The final UTF-EBCDIC byte has
         * dicontinuities which go away by transforming it into I8, and we
         * effectively subtract 0xA0 to get the index. */
        needents = (1 << UTF_ACCUMULATION_SHIFT);
        off      = NATIVE_UTF8_TO_I8(ptr[klen]) & UTF_CONTINUATION_MASK;
    }

    /*
     * This single-entry cache saves about 1/3 of the utf8 overhead in test
     * suite.  (That is, only 7-8% overall over just a hash cache.  Still,
     * it's nothing to sniff at.)  Pity we usually come through at least
     * two function calls to get here...
     *
     * NB: this code assumes that swatches are never modified, once generated!
     */

    if (hv   == PL_last_swash_hv &&
        klen == PL_last_swash_klen &&
        (!klen || memEQ((char *)ptr, (char *)PL_last_swash_key, klen)) )
    {
        tmps = PL_last_swash_tmps;
        slen = PL_last_swash_slen;
    }
    else {
        /* Try our second-level swatch cache, kept in a hash. */
        SV** svp = hv_fetch(hv, (const char*)ptr, klen, FALSE);

        /* If not cached, generate it via swatch_get */
        if (!svp || !SvPOK(*svp)
                 || !(tmps = (const U8*)SvPV_const(*svp, slen)))
        {
            if (klen) {
                const UV code_point = valid_utf8_to_uvchr(ptr, NULL);
                swatch = swatch_get(swash,
                                    code_point & ~((UV)needents - 1),
                                    needents);
            }
            else {  /* For the first 256 code points, the swatch has a key of
                       length 0 */
                swatch = swatch_get(swash, 0, needents);
            }

            if (IN_PERL_COMPILETIME)
                CopHINTS_set(PL_curcop, PL_hints);

            svp = hv_store(hv, (const char *)ptr, klen, swatch, 0);

            if (!svp || !(tmps = (U8*)SvPV(*svp, slen))
                     || (slen << 3) < needents)
                Perl_croak(aTHX_ "panic: swash_fetch got improper swatch, "
                           "svp=%p, tmps=%p, slen=%"UVuf", needents=%"UVuf,
                           svp, tmps, (UV)slen, (UV)needents);
        }

        PL_last_swash_hv = hv;
        assert(klen <= sizeof(PL_last_swash_key));
        PL_last_swash_klen = (U8)klen;
        /* FIXME change interpvar.h?  */
        PL_last_swash_tmps = (U8 *) tmps;
        PL_last_swash_slen = slen;
        if (klen)
            Copy(ptr, PL_last_swash_key, klen, U8);
    }

    switch ((int)((slen << 3) / needents)) {
    case 1:
        return ((UV) tmps[off >> 3] & (1 << (off & 7))) != 0;
    case 8:
        return ((UV) tmps[off]);
    case 16:
        off <<= 1;
        return
            ((UV) tmps[off    ] << 8) +
            ((UV) tmps[off + 1]);
    case 32:
        off <<= 2;
        return
            ((UV) tmps[off    ] << 24) +
            ((UV) tmps[off + 1] << 16) +
            ((UV) tmps[off + 2] <<  8) +
            ((UV) tmps[off + 3]);
    }
    Perl_croak(aTHX_ "panic: swash_fetch got swatch of unexpected bit width, "
               "slen=%"UVuf", needents=%"UVuf, (UV)slen, (UV)needents);
    NORETURN_FUNCTION_END;
}

/* Read a single line of the main body of the swash input text.  These are of
 * the form:
 * 0053 0056    0073
 * where each number is hex.  The first two numbers form the minimum and
 * maximum of a range, and the third is the value associated with the range.
 * Not all swashes should have a third number
 *
 * On input: l    points to the beginning of the line to be examined; it points
 *                to somewhere in the string of the whole input text, and is
 *                terminated by a \n or the null string terminator.
 *           lend   points to the null terminator of that string
 *           wants_value    is non-zero if the swash expects a third number
 *           typestr is the name of the swash's mapping, like 'ToLower'
 * On output: *min, *max, and *val are set to the values read from the line.
 *            returns a pointer just beyond the line examined.  If there was no
 *            valid min number on the line, returns lend+1
 */

STATIC U8*
S_swash_scan_list_line(pTHX_ U8* l, U8* const lend, UV* min, UV* max, UV* val,
                             const bool wants_value, const U8* const typestr)
{
    const int  typeto  = typestr[0] == 'T' && typestr[1] == 'o';
    STRLEN numlen;          /* Length of the number */
    I32 flags = PERL_SCAN_SILENT_ILLDIGIT
                | PERL_SCAN_DISALLOW_PREFIX
                | PERL_SCAN_SILENT_NON_PORTABLE;

    /* nl points to the next \n in the scan */
    U8* const nl = (U8*)memchr(l, '\n', lend - l);

    PERL_ARGS_ASSERT_SWASH_SCAN_LIST_LINE;

    /* Get the first number on the line: the range minimum */
    numlen = lend - l;
    *min = grok_hex((char *)l, &numlen, &flags, NULL);
    *max = *min;    /* So can never return without setting max */
    if (numlen)     /* If found a hex number, position past it */
        l += numlen;
    else if (nl) {          /* Else, go handle next line, if any */
        return nl + 1;  /* 1 is length of "\n" */
    }
    else {              /* Else, no next line */
        return lend + 1;        /* to LIST's end at which \n is not found */
    }

    /* The max range value follows, separated by a BLANK */
    if (isBLANK(*l)) {
        ++l;
        flags = PERL_SCAN_SILENT_ILLDIGIT
                | PERL_SCAN_DISALLOW_PREFIX
                | PERL_SCAN_SILENT_NON_PORTABLE;
        numlen = lend - l;
        *max = grok_hex((char *)l, &numlen, &flags, NULL);
        if (numlen)
            l += numlen;
        else    /* If no value here, it is a single element range */
            *max = *min;

        /* Non-binary tables have a third entry: what the first element of the
         * range maps to.  The map for those currently read here is in hex */
        if (wants_value) {
            if (isBLANK(*l)) {
                ++l;
                flags = PERL_SCAN_SILENT_ILLDIGIT
                    | PERL_SCAN_DISALLOW_PREFIX
                    | PERL_SCAN_SILENT_NON_PORTABLE;
                numlen = lend - l;
                *val = grok_hex((char *)l, &numlen, &flags, NULL);
                if (numlen)
                    l += numlen;
                else
                    *val = 0;
            }
            else {
                *val = 0;
                if (typeto) {
                    /* diag_listed_as: To%s: illegal mapping '%s' */
                    Perl_croak(aTHX_ "%s: illegal mapping '%s'",
                                     typestr, l);
                }
            }
        }
        else
            *val = 0; /* bits == 1, then any val should be ignored */
    }
    else { /* Nothing following range min, should be single element with no
              mapping expected */
        if (wants_value) {
            *val = 0;
            if (typeto) {
                /* diag_listed_as: To%s: illegal mapping '%s' */
                Perl_croak(aTHX_ "%s: illegal mapping '%s'", typestr, l);
            }
        }
        else
            *val = 0; /* bits == 1, then val should be ignored */
    }

    /* Position to next line if any, or EOF */
    if (nl)
        l = nl + 1;
    else
        l = lend;

    return l;
}

/* Note:
 * Returns a swatch (a bit vector string) for a code point sequence
 * that starts from the value C<start> and comprises the number C<span>.
 * A C<swash> must be an object created by SWASHNEW (see lib/utf8_heavy.pl).
 * Should be used via swash_fetch, which will cache the swatch in C<swash>.
 */
STATIC SV*
S_swatch_get(pTHX_ SV* swash, UV start, UV span)
{
    SV *swatch;
    U8 *l, *lend, *x, *xend, *s, *send;
    STRLEN lcur, xcur, scur;
    HV *const hv = MUTABLE_HV(SvRV(swash));
    SV** const invlistsvp = hv_fetchs(hv, "V", FALSE);

    SV** listsvp = NULL; /* The string containing the main body of the table */
    SV** extssvp = NULL;
    SV** invert_it_svp = NULL;
    U8* typestr = NULL;
    STRLEN bits;
    STRLEN octets; /* if bits == 1, then octets == 0 */
    UV  none;
    UV  end = start + span;

    if (invlistsvp == NULL) {
        SV** const bitssvp = hv_fetchs(hv, "BITS", FALSE);
        SV** const nonesvp = hv_fetchs(hv, "NONE", FALSE);
        SV** const typesvp = hv_fetchs(hv, "TYPE", FALSE);
        extssvp = hv_fetchs(hv, "EXTRAS", FALSE);
        listsvp = hv_fetchs(hv, "LIST", FALSE);
        invert_it_svp = hv_fetchs(hv, "INVERT_IT", FALSE);

        bits  = SvUV(*bitssvp);
        none  = SvUV(*nonesvp);
        typestr = (U8*)SvPV_nolen(*typesvp);
    }
    else {
        bits = 1;
        none = 0;
    }
    octets = bits >> 3; /* if bits == 1, then octets == 0 */

    PERL_ARGS_ASSERT_SWATCH_GET;

    if (bits != 1 && bits != 8 && bits != 16 && bits != 32) {
        Perl_croak(aTHX_ "panic: swatch_get doesn't expect bits %"UVuf,
                                                 (UV)bits);
    }

    /* If overflowed, use the max possible */
    if (end < start) {
        end = UV_MAX;
        span = end - start;
    }

    /* create and initialize $swatch */
    scur   = octets ? (span * octets) : (span + 7) / 8;
    swatch = newSV(scur);
    SvPOK_on(swatch);
    s = (U8*)SvPVX(swatch);
    if (octets && none) {
        const U8* const e = s + scur;
        while (s < e) {
            if (bits == 8)
                *s++ = (U8)(none & 0xff);
            else if (bits == 16) {
                *s++ = (U8)((none >>  8) & 0xff);
                *s++ = (U8)( none        & 0xff);
            }
            else if (bits == 32) {
                *s++ = (U8)((none >> 24) & 0xff);
                *s++ = (U8)((none >> 16) & 0xff);
                *s++ = (U8)((none >>  8) & 0xff);
                *s++ = (U8)( none        & 0xff);
            }
        }
        *s = '\0';
    }
    else {
        (void)memzero((U8*)s, scur + 1);
    }
    SvCUR_set(swatch, scur);
    s = (U8*)SvPVX(swatch);

    if (invlistsvp) {   /* If has an inversion list set up use that */
        _invlist_populate_swatch(*invlistsvp, start, end, s);
        return swatch;
    }

    /* read $swash->{LIST} */
    l = (U8*)SvPV(*listsvp, lcur);
    lend = l + lcur;
    while (l < lend) {
        UV min, max, val, upper;
        l = swash_scan_list_line(l, lend, &min, &max, &val,
                                                        cBOOL(octets), typestr);
        if (l > lend) {
            break;
        }

        /* If looking for something beyond this range, go try the next one */
        if (max < start)
            continue;

        /* <end> is generally 1 beyond where we want to set things, but at the
         * platform's infinity, where we can't go any higher, we want to
         * include the code point at <end> */
        upper = (max < end)
                ? max
                : (max != UV_MAX || end != UV_MAX)
                  ? end - 1
                  : end;

        if (octets) {
            UV key;
            if (min < start) {
                if (!none || val < none) {
                    val += start - min;
                }
                min = start;
            }
            for (key = min; key <= upper; key++) {
                STRLEN offset;
                /* offset must be non-negative (start <= min <= key < end) */
                offset = octets * (key - start);
                if (bits == 8)
                    s[offset] = (U8)(val & 0xff);
                else if (bits == 16) {
                    s[offset    ] = (U8)((val >>  8) & 0xff);
                    s[offset + 1] = (U8)( val        & 0xff);
                }
                else if (bits == 32) {
                    s[offset    ] = (U8)((val >> 24) & 0xff);
                    s[offset + 1] = (U8)((val >> 16) & 0xff);
                    s[offset + 2] = (U8)((val >>  8) & 0xff);
                    s[offset + 3] = (U8)( val        & 0xff);
                }

                if (!none || val < none)
                    ++val;
            }
        }
        else { /* bits == 1, then val should be ignored */
            UV key;
            if (min < start)
                min = start;

            for (key = min; key <= upper; key++) {
                const STRLEN offset = (STRLEN)(key - start);
                s[offset >> 3] |= 1 << (offset & 7);
            }
        }
    } /* while */

    /* Invert if the data says it should be.  Assumes that bits == 1 */
    if (invert_it_svp && SvUV(*invert_it_svp)) {

        /* Unicode properties should come with all bits above PERL_UNICODE_MAX
         * be 0, and their inversion should also be 0, as we don't succeed any
         * Unicode property matches for non-Unicode code points */
        if (start <= PERL_UNICODE_MAX) {

            /* The code below assumes that we never cross the
             * Unicode/above-Unicode boundary in a range, as otherwise we would
             * have to figure out where to stop flipping the bits.  Since this
             * boundary is divisible by a large power of 2, and swatches comes
             * in small powers of 2, this should be a valid assumption */
            assert(start + span - 1 <= PERL_UNICODE_MAX);

            send = s + scur;
            while (s < send) {
                *s = ~(*s);
                s++;
            }
        }
    }

    /* read $swash->{EXTRAS}
     * This code also copied to swash_to_invlist() below */
    x = (U8*)SvPV(*extssvp, xcur);
    xend = x + xcur;
    while (x < xend) {
        STRLEN namelen;
        U8 *namestr;
        SV** othersvp;
        HV* otherhv;
        STRLEN otherbits;
        SV **otherbitssvp, *other;
        U8 *s, *o, *nl;
        STRLEN slen, olen;

        const U8 opc = *x++;
        if (opc == '\n')
            continue;

        nl = (U8*)memchr(x, '\n', xend - x);

        if (opc != '-' && opc != '+' && opc != '!' && opc != '&') {
            if (nl) {
                x = nl + 1; /* 1 is length of "\n" */
                continue;
            }
            else {
                x = xend; /* to EXTRAS' end at which \n is not found */
                break;
            }
        }

        namestr = x;
        if (nl) {
            namelen = nl - namestr;
            x = nl + 1;
        }
        else {
            namelen = xend - namestr;
            x = xend;
        }

        othersvp = hv_fetch(hv, (char *)namestr, namelen, FALSE);
        otherhv = MUTABLE_HV(SvRV(*othersvp));
        otherbitssvp = hv_fetchs(otherhv, "BITS", FALSE);
        otherbits = (STRLEN)SvUV(*otherbitssvp);
        if (bits < otherbits)
            Perl_croak(aTHX_ "panic: swatch_get found swatch size mismatch, "
                       "bits=%"UVuf", otherbits=%"UVuf, (UV)bits, (UV)otherbits);

        /* The "other" swatch must be destroyed after. */
        other = swatch_get(*othersvp, start, span);
        o = (U8*)SvPV(other, olen);

        if (!olen)
            Perl_croak(aTHX_ "panic: swatch_get got improper swatch");

        s = (U8*)SvPV(swatch, slen);
        if (bits == 1 && otherbits == 1) {
            if (slen != olen)
                Perl_croak(aTHX_ "panic: swatch_get found swatch length "
                           "mismatch, slen=%"UVuf", olen=%"UVuf,
                           (UV)slen, (UV)olen);

            switch (opc) {
            case '+':
                while (slen--)
                    *s++ |= *o++;
                break;
            case '!':
                while (slen--)
                    *s++ |= ~*o++;
                break;
            case '-':
                while (slen--)
                    *s++ &= ~*o++;
                break;
            case '&':
                while (slen--)
                    *s++ &= *o++;
                break;
            default:
                break;
            }
        }
        else {
            STRLEN otheroctets = otherbits >> 3;
            STRLEN offset = 0;
            U8* const send = s + slen;

            while (s < send) {
                UV otherval = 0;

                if (otherbits == 1) {
                    otherval = (o[offset >> 3] >> (offset & 7)) & 1;
                    ++offset;
                }
                else {
                    STRLEN vlen = otheroctets;
                    otherval = *o++;
                    while (--vlen) {
                        otherval <<= 8;
                        otherval |= *o++;
                    }
                }

                if (opc == '+' && otherval)
                    NOOP;   /* replace with otherval */
                else if (opc == '!' && !otherval)
                    otherval = 1;
                else if (opc == '-' && otherval)
                    otherval = 0;
                else if (opc == '&' && !otherval)
                    otherval = 0;
                else {
                    s += octets; /* no replacement */
                    continue;
                }

                if (bits == 8)
                    *s++ = (U8)( otherval & 0xff);
                else if (bits == 16) {
                    *s++ = (U8)((otherval >>  8) & 0xff);
                    *s++ = (U8)( otherval        & 0xff);
                }
                else if (bits == 32) {
                    *s++ = (U8)((otherval >> 24) & 0xff);
                    *s++ = (U8)((otherval >> 16) & 0xff);
                    *s++ = (U8)((otherval >>  8) & 0xff);
                    *s++ = (U8)( otherval        & 0xff);
                }
            }
        }
        sv_free(other); /* through with it! */
    } /* while */
    return swatch;
}

HV*
Perl__swash_inversion_hash(pTHX_ SV* const swash)
{

   /* Subject to change or removal.  For use only in regcomp.c and regexec.c
    * Can't be used on a property that is subject to user override, as it
    * relies on the value of SPECIALS in the swash which would be set by
    * utf8_heavy.pl to the hash in the non-overriden file, and hence is not set
    * for overridden properties
    *
    * Returns a hash which is the inversion and closure of a swash mapping.
    * For example, consider the input lines:
    * 004B              006B
    * 004C              006C
    * 212A              006B
    *
    * The returned hash would have two keys, the utf8 for 006B and the utf8 for
    * 006C.  The value for each key is an array.  For 006C, the array would
    * have two elements, the utf8 for itself, and for 004C.  For 006B, there
    * would be three elements in its array, the utf8 for 006B, 004B and 212A.
    *
    * Note that there are no elements in the hash for 004B, 004C, 212A.  The
    * keys are only code points that are folded-to, so it isn't a full closure.
    *
    * Essentially, for any code point, it gives all the code points that map to
    * it, or the list of 'froms' for that point.
    *
    * Currently it ignores any additions or deletions from other swashes,
    * looking at just the main body of the swash, and if there are SPECIALS
    * in the swash, at that hash
    *
    * The specials hash can be extra code points, and most likely consists of
    * maps from single code points to multiple ones (each expressed as a string
    * of utf8 characters).   This function currently returns only 1-1 mappings.
    * However consider this possible input in the specials hash:
    * "\xEF\xAC\x85" => "\x{0073}\x{0074}",         # U+FB05 => 0073 0074
    * "\xEF\xAC\x86" => "\x{0073}\x{0074}",         # U+FB06 => 0073 0074
    *
    * Both FB05 and FB06 map to the same multi-char sequence, which we don't
    * currently handle.  But it also means that FB05 and FB06 are equivalent in
    * a 1-1 mapping which we should handle, and this relationship may not be in
    * the main table.  Therefore this function examines all the multi-char
    * sequences and adds the 1-1 mappings that come out of that.  */

    U8 *l, *lend;
    STRLEN lcur;
    HV *const hv = MUTABLE_HV(SvRV(swash));

    /* The string containing the main body of the table.  This will have its
     * assertion fail if the swash has been converted to its inversion list */
    SV** const listsvp = hv_fetchs(hv, "LIST", FALSE);

    SV** const typesvp = hv_fetchs(hv, "TYPE", FALSE);
    SV** const bitssvp = hv_fetchs(hv, "BITS", FALSE);
    SV** const nonesvp = hv_fetchs(hv, "NONE", FALSE);
    /*SV** const extssvp = hv_fetchs(hv, "EXTRAS", FALSE);*/
    const U8* const typestr = (U8*)SvPV_nolen(*typesvp);
    const STRLEN bits  = SvUV(*bitssvp);
    const STRLEN octets = bits >> 3; /* if bits == 1, then octets == 0 */
    const UV     none  = SvUV(*nonesvp);
    SV **specials_p = hv_fetchs(hv, "SPECIALS", 0);

    HV* ret = newHV();

    PERL_ARGS_ASSERT__SWASH_INVERSION_HASH;

    /* Must have at least 8 bits to get the mappings */
    if (bits != 8 && bits != 16 && bits != 32) {
        Perl_croak(aTHX_ "panic: swash_inversion_hash doesn't expect bits %"UVuf,
                                                 (UV)bits);
    }

    if (specials_p) { /* It might be "special" (sometimes, but not always, a
                        mapping to more than one character */

        /* Construct an inverse mapping hash for the specials */
        HV * const specials_hv = MUTABLE_HV(SvRV(*specials_p));
        HV * specials_inverse = newHV();
        char *char_from; /* the lhs of the map */
        I32 from_len;   /* its byte length */
        char *char_to;  /* the rhs of the map */
        I32 to_len;     /* its byte length */
        SV *sv_to;      /* and in a sv */
        AV* from_list;  /* list of things that map to each 'to' */

        hv_iterinit(specials_hv);

        /* The keys are the characters (in utf8) that map to the corresponding
         * utf8 string value.  Iterate through the list creating the inverse
         * list. */
        while ((sv_to = hv_iternextsv(specials_hv, &char_from, &from_len))) {
            SV** listp;
            if (! SvPOK(sv_to)) {
                Perl_croak(aTHX_ "panic: value returned from hv_iternextsv() "
                           "unexpectedly is not a string, flags=%lu",
                           (unsigned long)SvFLAGS(sv_to));
            }
            /*DEBUG_U(PerlIO_printf(Perl_debug_log, "Found mapping from %"UVXf", First char of to is %"UVXf"\n", valid_utf8_to_uvchr((U8*) char_from, 0), valid_utf8_to_uvchr((U8*) SvPVX(sv_to), 0)));*/

            /* Each key in the inverse list is a mapped-to value, and the key's
             * hash value is a list of the strings (each in utf8) that map to
             * it.  Those strings are all one character long */
            if ((listp = hv_fetch(specials_inverse,
                                    SvPVX(sv_to),
                                    SvCUR(sv_to), 0)))
            {
                from_list = (AV*) *listp;
            }
            else { /* No entry yet for it: create one */
                from_list = newAV();
                if (! hv_store(specials_inverse,
                                SvPVX(sv_to),
                                SvCUR(sv_to),
                                (SV*) from_list, 0))
                {
                    Perl_croak(aTHX_ "panic: hv_store() unexpectedly failed");
                }
            }

            /* Here have the list associated with this 'to' (perhaps newly
             * created and empty).  Just add to it.  Note that we ASSUME that
             * the input is guaranteed to not have duplications, so we don't
             * check for that.  Duplications just slow down execution time. */
            av_push(from_list, newSVpvn_utf8(char_from, from_len, TRUE));
        }

        /* Here, 'specials_inverse' contains the inverse mapping.  Go through
         * it looking for cases like the FB05/FB06 examples above.  There would
         * be an entry in the hash like
        *       'st' => [ FB05, FB06 ]
        * In this example we will create two lists that get stored in the
        * returned hash, 'ret':
        *       FB05 => [ FB05, FB06 ]
        *       FB06 => [ FB05, FB06 ]
        *
        * Note that there is nothing to do if the array only has one element.
        * (In the normal 1-1 case handled below, we don't have to worry about
        * two lists, as everything gets tied to the single list that is
        * generated for the single character 'to'.  But here, we are omitting
        * that list, ('st' in the example), so must have multiple lists.) */
        while ((from_list = (AV *) hv_iternextsv(specials_inverse,
                                                 &char_to, &to_len)))
        {
            if (av_tindex(from_list) > 0) {
                SSize_t i;

                /* We iterate over all combinations of i,j to place each code
                 * point on each list */
                for (i = 0; i <= av_tindex(from_list); i++) {
                    SSize_t j;
                    AV* i_list = newAV();
                    SV** entryp = av_fetch(from_list, i, FALSE);
                    if (entryp == NULL) {
                        Perl_croak(aTHX_ "panic: av_fetch() unexpectedly failed");
                    }
                    if (hv_fetch(ret, SvPVX(*entryp), SvCUR(*entryp), FALSE)) {
                        Perl_croak(aTHX_ "panic: unexpected entry for %s", SvPVX(*entryp));
                    }
                    if (! hv_store(ret, SvPVX(*entryp), SvCUR(*entryp),
                                   (SV*) i_list, FALSE))
                    {
                        Perl_croak(aTHX_ "panic: hv_store() unexpectedly failed");
                    }

                    /* For DEBUG_U: UV u = valid_utf8_to_uvchr((U8*) SvPVX(*entryp), 0);*/
                    for (j = 0; j <= av_tindex(from_list); j++) {
                        entryp = av_fetch(from_list, j, FALSE);
                        if (entryp == NULL) {
                            Perl_croak(aTHX_ "panic: av_fetch() unexpectedly failed");
                        }

                        /* When i==j this adds itself to the list */
                        av_push(i_list, newSVuv(utf8_to_uvchr_buf(
                                        (U8*) SvPVX(*entryp),
                                        (U8*) SvPVX(*entryp) + SvCUR(*entryp),
                                        0)));
                        /*DEBUG_U(PerlIO_printf(Perl_debug_log, "%s: %d: Adding %"UVXf" to list for %"UVXf"\n", __FILE__, __LINE__, valid_utf8_to_uvchr((U8*) SvPVX(*entryp), 0), u));*/
                    }
                }
            }
        }
        SvREFCNT_dec(specials_inverse); /* done with it */
    } /* End of specials */

    /* read $swash->{LIST} */
    l = (U8*)SvPV(*listsvp, lcur);
    lend = l + lcur;

    /* Go through each input line */
    while (l < lend) {
        UV min, max, val;
        UV inverse;
        l = swash_scan_list_line(l, lend, &min, &max, &val,
                                                     cBOOL(octets), typestr);
        if (l > lend) {
            break;
        }

        /* Each element in the range is to be inverted */
        for (inverse = min; inverse <= max; inverse++) {
            AV* list;
            SV** listp;
            IV i;
            bool found_key = FALSE;
            bool found_inverse = FALSE;

            /* The key is the inverse mapping */
            char key[UTF8_MAXBYTES+1];
            char* key_end = (char *) uvchr_to_utf8((U8*) key, val);
            STRLEN key_len = key_end - key;

            /* Get the list for the map */
            if ((listp = hv_fetch(ret, key, key_len, FALSE))) {
                list = (AV*) *listp;
            }
            else { /* No entry yet for it: create one */
                list = newAV();
                if (! hv_store(ret, key, key_len, (SV*) list, FALSE)) {
                    Perl_croak(aTHX_ "panic: hv_store() unexpectedly failed");
                }
            }

            /* Look through list to see if this inverse mapping already is
             * listed, or if there is a mapping to itself already */
            for (i = 0; i <= av_tindex(list); i++) {
                SV** entryp = av_fetch(list, i, FALSE);
                SV* entry;
                UV uv;
                if (entryp == NULL) {
                    Perl_croak(aTHX_ "panic: av_fetch() unexpectedly failed");
                }
                entry = *entryp;
                uv = SvUV(entry);
                /*DEBUG_U(PerlIO_printf(Perl_debug_log, "list for %"UVXf" contains %"UVXf"\n", val, uv));*/
                if (uv == val) {
                    found_key = TRUE;
                }
                if (uv == inverse) {
                    found_inverse = TRUE;
                }

                /* No need to continue searching if found everything we are
                 * looking for */
                if (found_key && found_inverse) {
                    break;
                }
            }

            /* Make sure there is a mapping to itself on the list */
            if (! found_key) {
                av_push(list, newSVuv(val));
                /*DEBUG_U(PerlIO_printf(Perl_debug_log, "%s: %d: Adding %"UVXf" to list for %"UVXf"\n", __FILE__, __LINE__, val, val));*/
            }


            /* Simply add the value to the list */
            if (! found_inverse) {
                av_push(list, newSVuv(inverse));
                /*DEBUG_U(PerlIO_printf(Perl_debug_log, "%s: %d: Adding %"UVXf" to list for %"UVXf"\n", __FILE__, __LINE__, inverse, val));*/
            }

            /* swatch_get() increments the value of val for each element in the
             * range.  That makes more compact tables possible.  You can
             * express the capitalization, for example, of all consecutive
             * letters with a single line: 0061\t007A\t0041 This maps 0061 to
             * 0041, 0062 to 0042, etc.  I (khw) have never understood 'none',
             * and it's not documented; it appears to be used only in
             * implementing tr//; I copied the semantics from swatch_get(), just
             * in case */
            if (!none || val < none) {
                ++val;
            }
        }
    }

    return ret;
}

SV*
Perl__swash_to_invlist(pTHX_ SV* const swash)
{

   /* Subject to change or removal.  For use only in one place in regcomp.c.
    * Ownership is given to one reference count in the returned SV* */

    U8 *l, *lend;
    char *loc;
    STRLEN lcur;
    HV *const hv = MUTABLE_HV(SvRV(swash));
    UV elements = 0;    /* Number of elements in the inversion list */
    U8 empty[] = "";
    SV** listsvp;
    SV** typesvp;
    SV** bitssvp;
    SV** extssvp;
    SV** invert_it_svp;

    U8* typestr;
    STRLEN bits;
    STRLEN octets; /* if bits == 1, then octets == 0 */
    U8 *x, *xend;
    STRLEN xcur;

    SV* invlist;

    PERL_ARGS_ASSERT__SWASH_TO_INVLIST;

    /* If not a hash, it must be the swash's inversion list instead */
    if (SvTYPE(hv) != SVt_PVHV) {
        return SvREFCNT_inc_simple_NN((SV*) hv);
    }

    /* The string containing the main body of the table */
    listsvp = hv_fetchs(hv, "LIST", FALSE);
    typesvp = hv_fetchs(hv, "TYPE", FALSE);
    bitssvp = hv_fetchs(hv, "BITS", FALSE);
    extssvp = hv_fetchs(hv, "EXTRAS", FALSE);
    invert_it_svp = hv_fetchs(hv, "INVERT_IT", FALSE);

    typestr = (U8*)SvPV_nolen(*typesvp);
    bits  = SvUV(*bitssvp);
    octets = bits >> 3; /* if bits == 1, then octets == 0 */

    /* read $swash->{LIST} */
    if (SvPOK(*listsvp)) {
        l = (U8*)SvPV(*listsvp, lcur);
    }
    else {
        /* LIST legitimately doesn't contain a string during compilation phases
         * of Perl itself, before the Unicode tables are generated.  In this
         * case, just fake things up by creating an empty list */
        l = empty;
        lcur = 0;
    }
    loc = (char *) l;
    lend = l + lcur;

    if (*l == 'V') {    /*  Inversion list format */
        const char *after_atou = (char *) lend;
        UV element0;
        UV* other_elements_ptr;

        /* The first number is a count of the rest */
        l++;
        elements = grok_atou((const char *)l, &after_atou);
        if (elements == 0) {
            invlist = _new_invlist(0);
        }
        else {
            while (isSPACE(*l)) l++;
            l = (U8 *) after_atou;

            /* Get the 0th element, which is needed to setup the inversion list */
            while (isSPACE(*l)) l++;
            element0 = (UV) grok_atou((const char *)l, &after_atou);
            l = (U8 *) after_atou;
            invlist = _setup_canned_invlist(elements, element0, &other_elements_ptr);
            elements--;

            /* Then just populate the rest of the input */
            while (elements-- > 0) {
                if (l > lend) {
                    Perl_croak(aTHX_ "panic: Expecting %"UVuf" more elements than available", elements);
                }
                while (isSPACE(*l)) l++;
                *other_elements_ptr++ = (UV) grok_atou((const char *)l, &after_atou);
                l = (U8 *) after_atou;
            }
        }
    }
    else {

        /* Scan the input to count the number of lines to preallocate array
         * size based on worst possible case, which is each line in the input
         * creates 2 elements in the inversion list: 1) the beginning of a
         * range in the list; 2) the beginning of a range not in the list.  */
        while ((loc = (strchr(loc, '\n'))) != NULL) {
            elements += 2;
            loc++;
        }

        /* If the ending is somehow corrupt and isn't a new line, add another
         * element for the final range that isn't in the inversion list */
        if (! (*lend == '\n'
            || (*lend == '\0' && (lcur == 0 || *(lend - 1) == '\n'))))
        {
            elements++;
        }

        invlist = _new_invlist(elements);

        /* Now go through the input again, adding each range to the list */
        while (l < lend) {
            UV start, end;
            UV val;             /* Not used by this function */

            l = swash_scan_list_line(l, lend, &start, &end, &val,
                                                        cBOOL(octets), typestr);

            if (l > lend) {
                break;
            }

            invlist = _add_range_to_invlist(invlist, start, end);
        }
    }

    /* Invert if the data says it should be */
    if (invert_it_svp && SvUV(*invert_it_svp)) {
        _invlist_invert(invlist);
    }

    /* This code is copied from swatch_get()
     * read $swash->{EXTRAS} */
    x = (U8*)SvPV(*extssvp, xcur);
    xend = x + xcur;
    while (x < xend) {
        STRLEN namelen;
        U8 *namestr;
        SV** othersvp;
        HV* otherhv;
        STRLEN otherbits;
        SV **otherbitssvp, *other;
        U8 *nl;

        const U8 opc = *x++;
        if (opc == '\n')
            continue;

        nl = (U8*)memchr(x, '\n', xend - x);

        if (opc != '-' && opc != '+' && opc != '!' && opc != '&') {
            if (nl) {
                x = nl + 1; /* 1 is length of "\n" */
                continue;
            }
            else {
                x = xend; /* to EXTRAS' end at which \n is not found */
                break;
            }
        }

        namestr = x;
        if (nl) {
            namelen = nl - namestr;
            x = nl + 1;
        }
        else {
            namelen = xend - namestr;
            x = xend;
        }

        othersvp = hv_fetch(hv, (char *)namestr, namelen, FALSE);
        otherhv = MUTABLE_HV(SvRV(*othersvp));
        otherbitssvp = hv_fetchs(otherhv, "BITS", FALSE);
        otherbits = (STRLEN)SvUV(*otherbitssvp);

        if (bits != otherbits || bits != 1) {
            Perl_croak(aTHX_ "panic: _swash_to_invlist only operates on boolean "
                       "properties, bits=%"UVuf", otherbits=%"UVuf,
                       (UV)bits, (UV)otherbits);
        }

        /* The "other" swatch must be destroyed after. */
        other = _swash_to_invlist((SV *)*othersvp);

        /* End of code copied from swatch_get() */
        switch (opc) {
        case '+':
            _invlist_union(invlist, other, &invlist);
            break;
        case '!':
            _invlist_union_maybe_complement_2nd(invlist, other, TRUE, &invlist);
            break;
        case '-':
            _invlist_subtract(invlist, other, &invlist);
            break;
        case '&':
            _invlist_intersection(invlist, other, &invlist);
            break;
        default:
            break;
        }
        sv_free(other); /* through with it! */
    }

    SvREADONLY_on(invlist);
    return invlist;
}

SV*
Perl__get_swash_invlist(pTHX_ SV* const swash)
{
    SV** ptr;

    PERL_ARGS_ASSERT__GET_SWASH_INVLIST;

    if (! SvROK(swash)) {
        return NULL;
    }

    /* If it really isn't a hash, it isn't really swash; must be an inversion
     * list */
    if (SvTYPE(SvRV(swash)) != SVt_PVHV) {
        return SvRV(swash);
    }

    ptr = hv_fetchs(MUTABLE_HV(SvRV(swash)), "V", FALSE);
    if (! ptr) {
        return NULL;
    }

    return *ptr;
}

bool
Perl_check_utf8_print(pTHX_ const U8* s, const STRLEN len)
{
    /* May change: warns if surrogates, non-character code points, or
     * non-Unicode code points are in s which has length len bytes.  Returns
     * TRUE if none found; FALSE otherwise.  The only other validity check is
     * to make sure that this won't exceed the string's length */

    const U8* const e = s + len;
    bool ok = TRUE;

    PERL_ARGS_ASSERT_CHECK_UTF8_PRINT;

    while (s < e) {
        if (UTF8SKIP(s) > len) {
            Perl_ck_warner_d(aTHX_ packWARN(WARN_UTF8),
                           "%s in %s", unees, PL_op ? OP_DESC(PL_op) : "print");
            return FALSE;
        }
        if (UNLIKELY(*s >= UTF8_FIRST_PROBLEMATIC_CODE_POINT_FIRST_BYTE)) {
            STRLEN char_len;
            if (UTF8_IS_SUPER(s)) {
                if (ckWARN_d(WARN_NON_UNICODE)) {
                    UV uv = utf8_to_uvchr_buf(s, e, &char_len);
                    Perl_warner(aTHX_ packWARN(WARN_NON_UNICODE),
                        "Code point 0x%04"UVXf" is not Unicode, may not be portable", uv);
                    ok = FALSE;
                }
            }
            else if (UTF8_IS_SURROGATE(s)) {
                if (ckWARN_d(WARN_SURROGATE)) {
                    UV uv = utf8_to_uvchr_buf(s, e, &char_len);
                    Perl_warner(aTHX_ packWARN(WARN_SURROGATE),
                        "Unicode surrogate U+%04"UVXf" is illegal in UTF-8", uv);
                    ok = FALSE;
                }
            }
            else if
                ((UTF8_IS_NONCHAR_GIVEN_THAT_NON_SUPER_AND_GE_PROBLEMATIC(s))
                 && (ckWARN_d(WARN_NONCHAR)))
            {
                UV uv = utf8_to_uvchr_buf(s, e, &char_len);
                Perl_warner(aTHX_ packWARN(WARN_NONCHAR),
                    "Unicode non-character U+%04"UVXf" is illegal for open interchange", uv);
                ok = FALSE;
            }
        }
        s += UTF8SKIP(s);
    }

    return ok;
}

/*
=for apidoc pv_uni_display

Build to the scalar C<dsv> a displayable version of the string C<spv>,
length C<len>, the displayable version being at most C<pvlim> bytes long
(if longer, the rest is truncated and "..." will be appended).

The C<flags> argument can have UNI_DISPLAY_ISPRINT set to display
isPRINT()able characters as themselves, UNI_DISPLAY_BACKSLASH
to display the \\[nrfta\\] as the backslashed versions (like '\n')
(UNI_DISPLAY_BACKSLASH is preferred over UNI_DISPLAY_ISPRINT for \\).
UNI_DISPLAY_QQ (and its alias UNI_DISPLAY_REGEX) have both
UNI_DISPLAY_BACKSLASH and UNI_DISPLAY_ISPRINT turned on.

The pointer to the PV of the C<dsv> is returned.

=cut */
char *
Perl_pv_uni_display(pTHX_ SV *dsv, const U8 *spv, STRLEN len, STRLEN pvlim, UV flags)
{
    int truncated = 0;
    const char *s, *e;

    PERL_ARGS_ASSERT_PV_UNI_DISPLAY;

    sv_setpvs(dsv, "");
    SvUTF8_off(dsv);
    for (s = (const char *)spv, e = s + len; s < e; s += UTF8SKIP(s)) {
         UV u;
          /* This serves double duty as a flag and a character to print after
             a \ when flags & UNI_DISPLAY_BACKSLASH is true.
          */
         char ok = 0;

         if (pvlim && SvCUR(dsv) >= pvlim) {
              truncated++;
              break;
         }
         u = utf8_to_uvchr_buf((U8*)s, (U8*)e, 0);
         if (u < 256) {
             const unsigned char c = (unsigned char)u & 0xFF;
             if (flags & UNI_DISPLAY_BACKSLASH) {
                 switch (c) {
                 case '\n':
                     ok = 'n'; break;
                 case '\r':
                     ok = 'r'; break;
                 case '\t':
                     ok = 't'; break;
                 case '\f':
                     ok = 'f'; break;
                 case '\a':
                     ok = 'a'; break;
                 case '\\':
                     ok = '\\'; break;
                 default: break;
                 }
                 if (ok) {
                     const char string = ok;
                     sv_catpvs(dsv, "\\");
                     sv_catpvn(dsv, &string, 1);
                 }
             }
             /* isPRINT() is the locale-blind version. */
             if (!ok && (flags & UNI_DISPLAY_ISPRINT) && isPRINT(c)) {
                 const char string = c;
                 sv_catpvn(dsv, &string, 1);
                 ok = 1;
             }
         }
         if (!ok)
             Perl_sv_catpvf(aTHX_ dsv, "\\x{%"UVxf"}", u);
    }
    if (truncated)
         sv_catpvs(dsv, "...");

    return SvPVX(dsv);
}

/*
=for apidoc sv_uni_display

Build to the scalar C<dsv> a displayable version of the scalar C<sv>,
the displayable version being at most C<pvlim> bytes long
(if longer, the rest is truncated and "..." will be appended).

The C<flags> argument is as in L</pv_uni_display>().

The pointer to the PV of the C<dsv> is returned.

=cut
*/
char *
Perl_sv_uni_display(pTHX_ SV *dsv, SV *ssv, STRLEN pvlim, UV flags)
{
    const char * const ptr =
        isREGEXP(ssv) ? RX_WRAPPED((REGEXP*)ssv) : SvPVX_const(ssv);

    PERL_ARGS_ASSERT_SV_UNI_DISPLAY;

    return Perl_pv_uni_display(aTHX_ dsv, (const U8*)ptr,
                                SvCUR(ssv), pvlim, flags);
}

/*
=for apidoc foldEQ_utf8

Returns true if the leading portions of the strings C<s1> and C<s2> (either or both
of which may be in UTF-8) are the same case-insensitively; false otherwise.
How far into the strings to compare is determined by other input parameters.

If C<u1> is true, the string C<s1> is assumed to be in UTF-8-encoded Unicode;
otherwise it is assumed to be in native 8-bit encoding.  Correspondingly for C<u2>
with respect to C<s2>.

If the byte length C<l1> is non-zero, it says how far into C<s1> to check for fold
equality.  In other words, C<s1>+C<l1> will be used as a goal to reach.  The
scan will not be considered to be a match unless the goal is reached, and
scanning won't continue past that goal.  Correspondingly for C<l2> with respect to
C<s2>.

If C<pe1> is non-NULL and the pointer it points to is not NULL, that pointer is
considered an end pointer to the position 1 byte past the maximum point
in C<s1> beyond which scanning will not continue under any circumstances.
(This routine assumes that UTF-8 encoded input strings are not malformed;
malformed input can cause it to read past C<pe1>).
This means that if both C<l1> and C<pe1> are specified, and C<pe1>
is less than C<s1>+C<l1>, the match will never be successful because it can
never
get as far as its goal (and in fact is asserted against).  Correspondingly for
C<pe2> with respect to C<s2>.

At least one of C<s1> and C<s2> must have a goal (at least one of C<l1> and
C<l2> must be non-zero), and if both do, both have to be
reached for a successful match.   Also, if the fold of a character is multiple
characters, all of them must be matched (see tr21 reference below for
'folding').

Upon a successful match, if C<pe1> is non-NULL,
it will be set to point to the beginning of the I<next> character of C<s1>
beyond what was matched.  Correspondingly for C<pe2> and C<s2>.

For case-insensitiveness, the "casefolding" of Unicode is used
instead of upper/lowercasing both the characters, see
L<http://www.unicode.org/unicode/reports/tr21/> (Case Mappings).

=cut */

/* A flags parameter has been added which may change, and hence isn't
 * externally documented.  Currently it is:
 *  0 for as-documented above
 *  FOLDEQ_UTF8_NOMIX_ASCII meaning that if a non-ASCII character folds to an
                            ASCII one, to not match
 *  FOLDEQ_LOCALE           is set iff the rules from the current underlying
 *                          locale are to be used.
 *  FOLDEQ_S1_ALREADY_FOLDED  s1 has already been folded before calling this
 *                          routine.  This allows that step to be skipped.
 *                          Currently, this requires s1 to be encoded as UTF-8
 *                          (u1 must be true), which is asserted for.
 *  FOLDEQ_S1_FOLDS_SANE    With either NOMIX_ASCII or LOCALE, no folds may
 *                          cross certain boundaries.  Hence, the caller should
 *                          let this function do the folding instead of
 *                          pre-folding.  This code contains an assertion to
 *                          that effect.  However, if the caller knows what
 *                          it's doing, it can pass this flag to indicate that,
 *                          and the assertion is skipped.
 *  FOLDEQ_S2_ALREADY_FOLDED  Similarly.
 *  FOLDEQ_S2_FOLDS_SANE
 */
I32
Perl_foldEQ_utf8_flags(pTHX_ const char *s1, char **pe1, UV l1, bool u1, const char *s2, char **pe2, UV l2, bool u2, U32 flags)
{
    const U8 *p1  = (const U8*)s1; /* Point to current char */
    const U8 *p2  = (const U8*)s2;
    const U8 *g1 = NULL;       /* goal for s1 */
    const U8 *g2 = NULL;
    const U8 *e1 = NULL;       /* Don't scan s1 past this */
    U8 *f1 = NULL;             /* Point to current folded */
    const U8 *e2 = NULL;
    U8 *f2 = NULL;
    STRLEN n1 = 0, n2 = 0;              /* Number of bytes in current char */
    U8 foldbuf1[UTF8_MAXBYTES_CASE+1];
    U8 foldbuf2[UTF8_MAXBYTES_CASE+1];
    U8 flags_for_folder = FOLD_FLAGS_FULL;

    PERL_ARGS_ASSERT_FOLDEQ_UTF8_FLAGS;

    assert( ! ((flags & (FOLDEQ_UTF8_NOMIX_ASCII | FOLDEQ_LOCALE))
               && (((flags & FOLDEQ_S1_ALREADY_FOLDED)
                     && !(flags & FOLDEQ_S1_FOLDS_SANE))
                   || ((flags & FOLDEQ_S2_ALREADY_FOLDED)
                       && !(flags & FOLDEQ_S2_FOLDS_SANE)))));
    /* The algorithm is to trial the folds without regard to the flags on
     * the first line of the above assert(), and then see if the result
     * violates them.  This means that the inputs can't be pre-folded to a
     * violating result, hence the assert.  This could be changed, with the
     * addition of extra tests here for the already-folded case, which would
     * slow it down.  That cost is more than any possible gain for when these
     * flags are specified, as the flags indicate /il or /iaa matching which
     * is less common than /iu, and I (khw) also believe that real-world /il
     * and /iaa matches are most likely to involve code points 0-255, and this
     * function only under rare conditions gets called for 0-255. */

    if (flags & FOLDEQ_LOCALE) {
        if (IN_UTF8_CTYPE_LOCALE) {
            flags &= ~FOLDEQ_LOCALE;
        }
        else {
            flags_for_folder |= FOLD_FLAGS_LOCALE;
        }
    }

    if (pe1) {
        e1 = *(U8**)pe1;
    }

    if (l1) {
        g1 = (const U8*)s1 + l1;
    }

    if (pe2) {
        e2 = *(U8**)pe2;
    }

    if (l2) {
        g2 = (const U8*)s2 + l2;
    }

    /* Must have at least one goal */
    assert(g1 || g2);

    if (g1) {

        /* Will never match if goal is out-of-bounds */
        assert(! e1  || e1 >= g1);

        /* Here, there isn't an end pointer, or it is beyond the goal.  We
        * only go as far as the goal */
        e1 = g1;
    }
    else {
        assert(e1);    /* Must have an end for looking at s1 */
    }

    /* Same for goal for s2 */
    if (g2) {
        assert(! e2  || e2 >= g2);
        e2 = g2;
    }
    else {
        assert(e2);
    }

    /* If both operands are already folded, we could just do a memEQ on the
     * whole strings at once, but it would be better if the caller realized
     * this and didn't even call us */

    /* Look through both strings, a character at a time */
    while (p1 < e1 && p2 < e2) {

        /* If at the beginning of a new character in s1, get its fold to use
         * and the length of the fold. */
        if (n1 == 0) {
            if (flags & FOLDEQ_S1_ALREADY_FOLDED) {
                f1 = (U8 *) p1;
                assert(u1);
                n1 = UTF8SKIP(f1);
            }
            else {
                if (isASCII(*p1) && ! (flags & FOLDEQ_LOCALE)) {

                    /* We have to forbid mixing ASCII with non-ASCII if the
                     * flags so indicate.  And, we can short circuit having to
                     * call the general functions for this common ASCII case,
                     * all of whose non-locale folds are also ASCII, and hence
                     * UTF-8 invariants, so the UTF8ness of the strings is not
                     * relevant. */
                    if ((flags & FOLDEQ_UTF8_NOMIX_ASCII) && ! isASCII(*p2)) {
                        return 0;
                    }
                    n1 = 1;
                    *foldbuf1 = toFOLD(*p1);
                }
                else if (u1) {
                    _to_utf8_fold_flags(p1, foldbuf1, &n1, flags_for_folder);
                }
                else {  /* Not utf8, get utf8 fold */
                    _to_uni_fold_flags(*p1, foldbuf1, &n1, flags_for_folder);
                }
                f1 = foldbuf1;
            }
        }

        if (n2 == 0) {    /* Same for s2 */
            if (flags & FOLDEQ_S2_ALREADY_FOLDED) {
                f2 = (U8 *) p2;
                assert(u2);
                n2 = UTF8SKIP(f2);
            }
            else {
                if (isASCII(*p2) && ! (flags & FOLDEQ_LOCALE)) {
                    if ((flags & FOLDEQ_UTF8_NOMIX_ASCII) && ! isASCII(*p1)) {
                        return 0;
                    }
                    n2 = 1;
                    *foldbuf2 = toFOLD(*p2);
                }
                else if (u2) {
                    _to_utf8_fold_flags(p2, foldbuf2, &n2, flags_for_folder);
                }
                else {
                    _to_uni_fold_flags(*p2, foldbuf2, &n2, flags_for_folder);
                }
                f2 = foldbuf2;
            }
        }

        /* Here f1 and f2 point to the beginning of the strings to compare.
         * These strings are the folds of the next character from each input
         * string, stored in utf8. */

        /* While there is more to look for in both folds, see if they
        * continue to match */
        while (n1 && n2) {
            U8 fold_length = UTF8SKIP(f1);
            if (fold_length != UTF8SKIP(f2)
                || (fold_length == 1 && *f1 != *f2) /* Short circuit memNE
                                                       function call for single
                                                       byte */
                || memNE((char*)f1, (char*)f2, fold_length))
            {
                return 0; /* mismatch */
            }

            /* Here, they matched, advance past them */
            n1 -= fold_length;
            f1 += fold_length;
            n2 -= fold_length;
            f2 += fold_length;
        }

        /* When reach the end of any fold, advance the input past it */
        if (n1 == 0) {
            p1 += u1 ? UTF8SKIP(p1) : 1;
        }
        if (n2 == 0) {
            p2 += u2 ? UTF8SKIP(p2) : 1;
        }
    } /* End of loop through both strings */

    /* A match is defined by each scan that specified an explicit length
    * reaching its final goal, and the other not having matched a partial
    * character (which can happen when the fold of a character is more than one
    * character). */
    if (! ((g1 == 0 || p1 == g1) && (g2 == 0 || p2 == g2)) || n1 || n2) {
        return 0;
    }

    /* Successful match.  Set output pointers */
    if (pe1) {
        *pe1 = (char*)p1;
    }
    if (pe2) {
        *pe2 = (char*)p2;
    }
    return 1;
}

/* XXX The next two functions should likely be moved to mathoms.c once all
 * occurrences of them are removed from the core; some cpan-upstream modules
 * still use them */

U8 *
Perl_uvuni_to_utf8(pTHX_ U8 *d, UV uv)
{
    PERL_ARGS_ASSERT_UVUNI_TO_UTF8;

    return Perl_uvoffuni_to_utf8_flags(aTHX_ d, uv, 0);
}

/*
=for apidoc utf8n_to_uvuni

Instead use L</utf8_to_uvchr_buf>, or rarely, L</utf8n_to_uvchr>.

This function was useful for code that wanted to handle both EBCDIC and
ASCII platforms with Unicode properties, but starting in Perl v5.20, the
distinctions between the platforms have mostly been made invisible to most
code, so this function is quite unlikely to be what you want.  If you do need
this precise functionality, use instead
C<L<NATIVE_TO_UNI(utf8_to_uvchr_buf(...))|/utf8_to_uvchr_buf>>
or C<L<NATIVE_TO_UNI(utf8n_to_uvchr(...))|/utf8n_to_uvchr>>.

=cut
*/

UV
Perl_utf8n_to_uvuni(pTHX_ const U8 *s, STRLEN curlen, STRLEN *retlen, U32 flags)
{
    PERL_ARGS_ASSERT_UTF8N_TO_UVUNI;

    return NATIVE_TO_UNI(utf8n_to_uvchr(s, curlen, retlen, flags));
}

/*
=for apidoc uvuni_to_utf8_flags

Instead you almost certainly want to use L</uvchr_to_utf8> or
L</uvchr_to_utf8_flags>>.

This function is a deprecated synonym for L</uvoffuni_to_utf8_flags>,
which itself, while not deprecated, should be used only in isolated
circumstances.  These functions were useful for code that wanted to handle
both EBCDIC and ASCII platforms with Unicode properties, but starting in Perl
v5.20, the distinctions between the platforms have mostly been made invisible
to most code, so this function is quite unlikely to be what you want.

=cut
*/

U8 *
Perl_uvuni_to_utf8_flags(pTHX_ U8 *d, UV uv, UV flags)
{
    PERL_ARGS_ASSERT_UVUNI_TO_UTF8_FLAGS;

    return uvoffuni_to_utf8_flags(d, uv, flags);
}

/*
 * Local variables:
 * c-indentation-style: bsd
 * c-basic-offset: 4
 * indent-tabs-mode: nil
 * End:
 *
 * ex: set ts=8 sts=4 sw=4 et:
 */