This is a live mirror of the Perl 5 development currently hosted at https://github.com/perl/perl5
For character case changing, create macros and use
[perl5.git] / utf8.c
diff --git a/utf8.c b/utf8.c
index 5fdaf52..94c5d81 100644 (file)
--- a/utf8.c
+++ b/utf8.c
 #include "perl.h"
 #include "invlist_inline.h"
 
+static const char malformed_text[] = "Malformed UTF-8 character";
 static const char unees[] =
-    "Malformed UTF-8 character (unexpected end of string)";
+                        "Malformed UTF-8 character (unexpected end of string)";
 static const char cp_above_legal_max[] =
- "Use of code point 0x%"UVXf" is deprecated; the permissible max is 0x%"UVXf"";
+ "Use of code point 0x%" UVXf " is deprecated; the permissible max is 0x%" UVXf;
 
 #define MAX_NON_DEPRECATED_CP ((UV) (IV_MAX))
 
@@ -51,6 +52,54 @@ within non-zero characters.
 =cut
 */
 
+void
+Perl__force_out_malformed_utf8_message(pTHX_
+            const U8 *const p,      /* First byte in UTF-8 sequence */
+            const U8 * const e,     /* Final byte in sequence (may include
+                                       multiple chars */
+            const U32 flags,        /* Flags to pass to utf8n_to_uvchr(),
+                                       usually 0, or some DISALLOW flags */
+            const bool die_here)    /* If TRUE, this function does not return */
+{
+    /* This core-only function is to be called when a malformed UTF-8 character
+     * is found, in order to output the detailed information about the
+     * malformation before dieing.  The reason it exists is for the occasions
+     * when such a malformation is fatal, but warnings might be turned off, so
+     * that normally they would not be actually output.  This ensures that they
+     * do get output.  Because a sequence may be malformed in more than one
+     * way, multiple messages may be generated, so we can't make them fatal, as
+     * that would cause the first one to die.
+     *
+     * Instead we pretend -W was passed to perl, then die afterwards.  The
+     * flexibility is here to return to the caller so they can finish up and
+     * die themselves */
+    U32 errors;
+
+    PERL_ARGS_ASSERT__FORCE_OUT_MALFORMED_UTF8_MESSAGE;
+
+    ENTER;
+    SAVESPTR(PL_dowarn);
+    SAVESPTR(PL_curcop);
+
+    PL_dowarn = G_WARN_ALL_ON|G_WARN_ON;
+    if (PL_curcop) {
+        PL_curcop->cop_warnings = pWARN_ALL;
+    }
+
+    (void) utf8n_to_uvchr_error(p, e - p, NULL, flags & ~UTF8_CHECK_ONLY, &errors);
+
+    LEAVE;
+
+    if (! errors) {
+       Perl_croak(aTHX_ "panic: _force_out_malformed_utf8_message should"
+                         " be called only when there are errors found");
+    }
+
+    if (die_here) {
+        Perl_croak(aTHX_ "Malformed UTF-8 character (fatal)");
+    }
+}
+
 /*
 =for apidoc uvoffuni_to_utf8_flags
 
@@ -71,7 +120,7 @@ For details, see the description for L</uvchr_to_utf8_flags>.
     STMT_START {                                                    \
         if (flags & UNICODE_WARN_SURROGATE) {                       \
             Perl_ck_warner_d(aTHX_ packWARN(WARN_SURROGATE),        \
-                                "UTF-16 surrogate U+%04"UVXf, uv);  \
+                                "UTF-16 surrogate U+%04" UVXf, uv); \
         }                                                           \
         if (flags & UNICODE_DISALLOW_SURROGATE) {                   \
             return NULL;                                            \
@@ -82,7 +131,7 @@ For details, see the description for L</uvchr_to_utf8_flags>.
     STMT_START {                                                    \
         if (flags & UNICODE_WARN_NONCHAR) {                         \
             Perl_ck_warner_d(aTHX_ packWARN(WARN_NONCHAR),          \
-                "Unicode non-character U+%04"UVXf" is not "        \
+                "Unicode non-character U+%04" UVXf " is not "      \
                  "recommended for open interchange", uv);           \
         }                                                           \
         if (flags & UNICODE_DISALLOW_NONCHAR) {                     \
@@ -163,8 +212,8 @@ Perl_uvoffuni_to_utf8_flags(pTHX_ U8 *d, UV uv, UV flags)
 
               /* Choose the more dire applicable warning */
               (UNICODE_IS_ABOVE_31_BIT(uv))
-              ? "Code point 0x%"UVXf" is not Unicode, and not portable"
-              : "Code point 0x%"UVXf" is not Unicode, may not be portable",
+              ? "Code point 0x%" UVXf " is not Unicode, and not portable"
+              : "Code point 0x%" UVXf " is not Unicode, may not be portable",
              uv);
         }
         if (flags & UNICODE_DISALLOW_SUPER
@@ -381,15 +430,12 @@ S_is_utf8_cp_above_31_bits(const U8 * const s, const U8 * const e)
      */
 
 #ifdef EBCDIC
-#  ifndef MIN
-#    define MIN(a,b) ((a) < (b) ? (a) : (b))
-#  endif
 
-        /* [0] is start byte    [1] [2] [3] [4] [5] [6] [7] */
-    const U8 * const prefix = "\x41\x41\x41\x41\x41\x41\x42";
+    /* [0] is start byte  [1] [2] [3] [4] [5] [6] [7] */
+    const U8 prefix[] = "\x41\x41\x41\x41\x41\x41\x42";
     const STRLEN prefix_len = sizeof(prefix) - 1;
     const STRLEN len = e - s;
-    const cmp_len = MIN(prefix_len, len - 1);
+    const STRLEN cmp_len = MIN(prefix_len, len - 1);
 
 #else
 
@@ -426,11 +472,151 @@ S_is_utf8_cp_above_31_bits(const U8 * const s, const U8 * const e)
 
 }
 
+PERL_STATIC_INLINE bool
+S_does_utf8_overflow(const U8 * const s, const U8 * e)
+{
+    const U8 *x;
+    const U8 * y = (const U8 *) HIGHEST_REPRESENTABLE_UTF8;
+
+#if ! defined(UV_IS_QUAD) && ! defined(EBCDIC)
+
+    const STRLEN len = e - s;
+
+#endif
+
+    /* Returns a boolean as to if this UTF-8 string would overflow a UV on this
+     * platform, that is if it represents a code point larger than the highest
+     * representable code point.  (For ASCII platforms, we could use memcmp()
+     * because we don't have to convert each byte to I8, but it's very rare
+     * input indeed that would approach overflow, so the loop below will likely
+     * only get executed once.
+     *
+     * 'e' must not be beyond a full character.  If it is less than a full
+     * character, the function returns FALSE if there is any input beyond 'e'
+     * that could result in a non-overflowing code point */
+
+    PERL_ARGS_ASSERT_DOES_UTF8_OVERFLOW;
+    assert(s <= e && s + UTF8SKIP(s) >= e);
+
+#if ! defined(UV_IS_QUAD) && ! defined(EBCDIC)
+
+    /* On 32 bit ASCII machines, many overlongs that start with FF don't
+     * overflow */
+
+    if (isFF_OVERLONG(s, len)) {
+        const U8 max_32_bit_overlong[] = "\xFF\x80\x80\x80\x80\x80\x80\x84";
+        return memGE(s, max_32_bit_overlong,
+                                MIN(len, sizeof(max_32_bit_overlong) - 1));
+    }
+
+#endif
+
+    for (x = s; x < e; x++, y++) {
+
+        /* If this byte is larger than the corresponding highest UTF-8 byte, it
+         * overflows */
+        if (UNLIKELY(NATIVE_UTF8_TO_I8(*x) > *y)) {
+            return TRUE;
+        }
+
+        /* If not the same as this byte, it must be smaller, doesn't overflow */
+        if (LIKELY(NATIVE_UTF8_TO_I8(*x) != *y)) {
+            return FALSE;
+        }
+    }
+
+    /* Got to the end and all bytes are the same.  If the input is a whole
+     * character, it doesn't overflow.  And if it is a partial character,
+     * there's not enough information to tell, so assume doesn't overflow */
+    return FALSE;
+}
+
+PERL_STATIC_INLINE bool
+S_is_utf8_overlong_given_start_byte_ok(const U8 * const s, const STRLEN len)
+{
+    /* Overlongs can occur whenever the number of continuation bytes
+     * changes.  That means whenever the number of leading 1 bits in a start
+     * byte increases from the next lower start byte.  That happens for start
+     * bytes C0, E0, F0, F8, FC, FE, and FF.  On modern perls, the following
+     * illegal start bytes have already been excluded, so don't need to be
+     * tested here;
+     * ASCII platforms: C0, C1
+     * EBCDIC platforms C0, C1, C2, C3, C4, E0
+     *
+     * At least a second byte is required to determine if other sequences will
+     * be an overlong. */
+
+    const U8 s0 = NATIVE_UTF8_TO_I8(s[0]);
+    const U8 s1 = NATIVE_UTF8_TO_I8(s[1]);
+
+    PERL_ARGS_ASSERT_IS_UTF8_OVERLONG_GIVEN_START_BYTE_OK;
+    assert(len > 1 && UTF8_IS_START(*s));
+
+    /* Each platform has overlongs after the start bytes given above (expressed
+     * in I8 for EBCDIC).  What constitutes an overlong varies by platform, but
+     * the logic is the same, except the E0 overlong has already been excluded
+     * on EBCDIC platforms.   The  values below were found by manually
+     * inspecting the UTF-8 patterns.  See the tables in utf8.h and
+     * utfebcdic.h. */
+
+#       ifdef EBCDIC
+#           define F0_ABOVE_OVERLONG 0xB0
+#           define F8_ABOVE_OVERLONG 0xA8
+#           define FC_ABOVE_OVERLONG 0xA4
+#           define FE_ABOVE_OVERLONG 0xA2
+#           define FF_OVERLONG_PREFIX "\xfe\x41\x41\x41\x41\x41\x41\x41"
+                                    /* I8(0xfe) is FF */
+#       else
+
+    if (s0 == 0xE0 && UNLIKELY(s1 < 0xA0)) {
+        return TRUE;
+    }
+
+#           define F0_ABOVE_OVERLONG 0x90
+#           define F8_ABOVE_OVERLONG 0x88
+#           define FC_ABOVE_OVERLONG 0x84
+#           define FE_ABOVE_OVERLONG 0x82
+#           define FF_OVERLONG_PREFIX "\xff\x80\x80\x80\x80\x80\x80"
+#       endif
+
+
+    if (   (s0 == 0xF0 && UNLIKELY(s1 < F0_ABOVE_OVERLONG))
+        || (s0 == 0xF8 && UNLIKELY(s1 < F8_ABOVE_OVERLONG))
+        || (s0 == 0xFC && UNLIKELY(s1 < FC_ABOVE_OVERLONG))
+        || (s0 == 0xFE && UNLIKELY(s1 < FE_ABOVE_OVERLONG)))
+    {
+        return TRUE;
+    }
+
+    /* Check for the FF overlong */
+    return isFF_OVERLONG(s, len);
+}
+
+PERL_STATIC_INLINE bool
+S_isFF_OVERLONG(const U8 * const s, const STRLEN len)
+{
+    PERL_ARGS_ASSERT_ISFF_OVERLONG;
+
+    /* Check for the FF overlong.  This happens only if all these bytes match;
+     * what comes after them doesn't matter.  See tables in utf8.h,
+     * utfebcdic.h. */
+
+    return    len >= sizeof(FF_OVERLONG_PREFIX) - 1
+           && UNLIKELY(memEQ(s, FF_OVERLONG_PREFIX,
+                                            sizeof(FF_OVERLONG_PREFIX) - 1));
+}
+
+#undef F0_ABOVE_OVERLONG
+#undef F8_ABOVE_OVERLONG
+#undef FC_ABOVE_OVERLONG
+#undef FE_ABOVE_OVERLONG
+#undef FF_OVERLONG_PREFIX
+
 STRLEN
 Perl__is_utf8_char_helper(const U8 * const s, const U8 * e, const U32 flags)
 {
     STRLEN len;
-    const U8 *x, *y;
+    const U8 *x;
 
     /* A helper function that should not be called directly.
      *
@@ -500,18 +686,20 @@ Perl__is_utf8_char_helper(const U8 * const s, const U8 * e, const U32 flags)
 
 #ifdef EBCDIC   /* On EBCDIC, these are actually I8 bytes */
 #  define FIRST_START_BYTE_THAT_IS_DEFINITELY_SUPER  0xFA
-#  define IS_SUPER_2_BYTE(s0, s1)                ((s0) == 0xF9 && (s1) >= 0xA2)
+#  define IS_UTF8_2_BYTE_SUPER(s0, s1)           ((s0) == 0xF9 && (s1) >= 0xA2)
 
-                                                               /* B6 and B7 */
-#  define IS_SURROGATE(s0, s1)         ((s0) == 0xF1 && ((s1) & 0xFE ) == 0xB6)
+#  define IS_UTF8_2_BYTE_SURROGATE(s0, s1)       ((s0) == 0xF1              \
+                                                       /* B6 and B7 */      \
+                                              && ((s1) & 0xFE ) == 0xB6)
 #else
 #  define FIRST_START_BYTE_THAT_IS_DEFINITELY_SUPER  0xF5
-#  define IS_SUPER_2_BYTE(s0, s1)                ((s0) == 0xF4 && (s1) >= 0x90)
-#  define IS_SURROGATE(s0, s1)                   ((s0) == 0xED && (s1) >= 0xA0)
+#  define IS_UTF8_2_BYTE_SUPER(s0, s1)           ((s0) == 0xF4 && (s1) >= 0x90)
+#  define IS_UTF8_2_BYTE_SURROGATE(s0, s1)       ((s0) == 0xED && (s1) >= 0xA0)
 #endif
 
         if (  (flags & UTF8_DISALLOW_SUPER)
-            && UNLIKELY(s0 >= FIRST_START_BYTE_THAT_IS_DEFINITELY_SUPER)) {
+            && UNLIKELY(s0 >= FIRST_START_BYTE_THAT_IS_DEFINITELY_SUPER))
+        {
             return 0;           /* Above Unicode */
         }
 
@@ -525,13 +713,13 @@ Perl__is_utf8_char_helper(const U8 * const s, const U8 * e, const U32 flags)
             const U8 s1 = NATIVE_UTF8_TO_I8(s[1]);
 
             if (   (flags & UTF8_DISALLOW_SUPER)
-                &&  UNLIKELY(IS_SUPER_2_BYTE(s0, s1)))
+                &&  UNLIKELY(IS_UTF8_2_BYTE_SUPER(s0, s1)))
             {
                 return 0;       /* Above Unicode */
             }
 
             if (   (flags & UTF8_DISALLOW_SURROGATE)
-                &&  UNLIKELY(IS_SURROGATE(s0, s1)))
+                &&  UNLIKELY(IS_UTF8_2_BYTE_SURROGATE(s0, s1)))
             {
                 return 0;       /* Surrogate */
             }
@@ -552,112 +740,101 @@ Perl__is_utf8_char_helper(const U8 * const s, const U8 * e, const U32 flags)
     }
 
     /* Here is syntactically valid.  Next, make sure this isn't the start of an
-     * overlong.  Overlongs can occur whenever the number of continuation bytes
-     * changes.  That means whenever the number of leading 1 bits in a start
-     * byte increases from the next lower start byte.  That happens for start
-     * bytes C0, E0, F0, F8, FC, FE, and FF.  On modern perls, the following
-     * illegal start bytes have already been excluded, so don't need to be
-     * tested here;
-     * ASCII platforms: C0, C1
-     * EBCDIC platforms C0, C1, C2, C3, C4, E0
-     *
-     * At least a second byte is required to determine if other sequences will
-     * be an overlong. */
-
-    if (len > 1) {
-        const U8 s0 = NATIVE_UTF8_TO_I8(s[0]);
-        const U8 s1 = NATIVE_UTF8_TO_I8(s[1]);
+     * overlong. */
+    if (len > 1 && is_utf8_overlong_given_start_byte_ok(s, len)) {
+        return 0;
+    }
 
-        /* Each platform has overlongs after the start bytes given above
-         * (expressed in I8 for EBCDIC).  What constitutes an overlong varies
-         * by platform, but the logic is the same, except the E0 overlong has
-         * already been excluded on EBCDIC platforms.   The  values below were
-         * found by manually inspecting the UTF-8 patterns.  See the tables in
-         * utf8.h and utfebcdic.h */
+    /* And finally, that the code point represented fits in a word on this
+     * platform */
+    if (does_utf8_overflow(s, e)) {
+        return 0;
+    }
 
-#       ifdef EBCDIC
-#           define F0_ABOVE_OVERLONG 0xB0
-#           define F8_ABOVE_OVERLONG 0xA8
-#           define FC_ABOVE_OVERLONG 0xA4
-#           define FE_ABOVE_OVERLONG 0xA2
-#           define FF_OVERLONG_PREFIX "\xfe\x41\x41\x41\x41\x41\x41\x41"
-                                      /* I8(0xfe) is FF */
-#       else
+    return UTF8SKIP(s);
+}
 
-        if (s0 == 0xE0 && UNLIKELY(s1 < 0xA0)) {
-            return 0;       /* Overlong */
-        }
+STATIC char *
+S__byte_dump_string(pTHX_ const U8 * s, const STRLEN len)
+{
+    /* Returns a mortalized C string that is a displayable copy of the 'len'
+     * bytes starting at 's', each in a \xXY format. */
 
-#           define F0_ABOVE_OVERLONG 0x90
-#           define F8_ABOVE_OVERLONG 0x88
-#           define FC_ABOVE_OVERLONG 0x84
-#           define FE_ABOVE_OVERLONG 0x82
-#           define FF_OVERLONG_PREFIX "\xff\x80\x80\x80\x80\x80\x80"
-#       endif
+    const STRLEN output_len = 4 * len + 1;  /* 4 bytes per each input, plus a
+                                               trailing NUL */
+    const U8 * const e = s + len;
+    char * output;
+    char * d;
 
+    PERL_ARGS_ASSERT__BYTE_DUMP_STRING;
 
-        if (   (s0 == 0xF0 && UNLIKELY(s1 < F0_ABOVE_OVERLONG))
-            || (s0 == 0xF8 && UNLIKELY(s1 < F8_ABOVE_OVERLONG))
-            || (s0 == 0xFC && UNLIKELY(s1 < FC_ABOVE_OVERLONG))
-            || (s0 == 0xFE && UNLIKELY(s1 < FE_ABOVE_OVERLONG)))
-        {
-            return 0;       /* Overlong */
-        }
+    Newx(output, output_len, char);
+    SAVEFREEPV(output);
 
-#   if defined(UV_IS_QUAD) || defined(EBCDIC)
+    d = output;
+    for (; s < e; s++) {
+        const unsigned high_nibble = (*s & 0xF0) >> 4;
+        const unsigned low_nibble =  (*s & 0x0F);
 
-        /* Check for the FF overlong.  This happens only if all these bytes
-         * match; what comes after them doesn't matter.  See tables in utf8.h,
-         * utfebcdic.h.  (Can't happen on ASCII 32-bit platforms, as overflows
-         * instead.) */
+        *d++ = '\\';
+        *d++ = 'x';
 
-        if (   len >= sizeof(FF_OVERLONG_PREFIX) - 1
-            && UNLIKELY(memEQ(s, FF_OVERLONG_PREFIX,
-                                               sizeof(FF_OVERLONG_PREFIX) - 1)))
-        {
-            return 0;       /* Overlong */
+        if (high_nibble < 10) {
+            *d++ = high_nibble + '0';
+        }
+        else {
+            *d++ = high_nibble - 10 + 'a';
         }
 
-#endif
-
+        if (low_nibble < 10) {
+            *d++ = low_nibble + '0';
+        }
+        else {
+            *d++ = low_nibble - 10 + 'a';
+        }
     }
 
-    /* Finally, see if this would overflow a UV on this platform.  See if the
-     * UTF8 for this code point is larger than that for the highest
-     * representable code point.  (For ASCII platforms, we could use memcmp()
-     * because we don't have to convert each byte to I8, but it's very rare
-     * input indeed that would approach overflow, so the loop below will likely
-     * only get executed once */
-    y = (const U8 *) HIGHEST_REPRESENTABLE_UTF8;
-
-    for (x = s; x < e; x++, y++) {
+    *d = '\0';
+    return output;
+}
 
-        /* If the same as this byte, go on to the next */
-        if (UNLIKELY(NATIVE_UTF8_TO_I8(*x) == *y)) {
-            continue;
-        }
+PERL_STATIC_INLINE char *
+S_unexpected_non_continuation_text(pTHX_ const U8 * const s,
 
-        /* If this is larger, it overflows */
-        if (UNLIKELY(NATIVE_UTF8_TO_I8(*x) > *y)) {
-            return 0;
-        }
+                                         /* How many bytes to print */
+                                         STRLEN print_len,
 
-        /* But if smaller, it won't */
-        break;
-    }
+                                         /* Which one is the non-continuation */
+                                         const STRLEN non_cont_byte_pos,
 
-    return UTF8SKIP(s);
+                                         /* How many bytes should there be? */
+                                         const STRLEN expect_len)
+{
+    /* Return the malformation warning text for an unexpected continuation
+     * byte. */
+
+    const char * const where = (non_cont_byte_pos == 1)
+                               ? "immediately"
+                               : Perl_form(aTHX_ "%d bytes",
+                                                 (int) non_cont_byte_pos);
+
+    PERL_ARGS_ASSERT_UNEXPECTED_NON_CONTINUATION_TEXT;
+
+    /* We don't need to pass this parameter, but since it has already been
+     * calculated, it's likely faster to pass it; verify under DEBUGGING */
+    assert(expect_len == UTF8SKIP(s));
+
+    return Perl_form(aTHX_ "%s: %s (unexpected non-continuation byte 0x%02x,"
+                           " %s after start byte 0x%02x; need %d bytes, got %d)",
+                           malformed_text,
+                           _byte_dump_string(s, print_len),
+                           *(s + non_cont_byte_pos),
+                           where,
+                           *s,
+                           (int) expect_len,
+                           (int) non_cont_byte_pos);
 }
 
-#undef FIRST_START_BYTE_THAT_IS_DEFINITELY_SUPER
-#undef IS_SUPER_2_BYTE
-#undef IS_SURROGATE
-#undef F0_ABOVE_OVERLONG
-#undef F8_ABOVE_OVERLONG
-#undef FC_ABOVE_OVERLONG
-#undef FE_ABOVE_OVERLONG
-#undef FF_OVERLONG_PREFIX
-
 /*
 
 =for apidoc utf8n_to_uvchr
@@ -672,10 +849,13 @@ 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.
+well-formed UTF-8 character.  If C<flags> is 0, encountering a malformation
+causes zero to be 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.  Some UTF-8 input sequences may contain multiple malformations.
+This function tries to find every possible one in each call, so multiple
+warnings can be raised for each sequence.
 
 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
@@ -683,10 +863,10 @@ 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.
+flags.  Even if allowed, this function generally returns the Unicode
+REPLACEMENT CHARACTER when it encounters a malformation.  There are flags in
+F<utf8.h> to override this behavior for the overlong malformations, but don't
+do that except for very specialized purposes.
 
 The C<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
@@ -698,7 +878,7 @@ character, and an error return (unless the C<UTF8_CHECK_ONLY> flag is set), as
 in both cases, 0 is returned, and, depending on the malformation, C<retlen> may
 be set to 1.  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.
+error.  Or you can use C<L</utf8n_to_uvchr_error>>.
 
 Certain code points are considered problematic.  These are Unicode surrogates,
 Unicode non-characters, and code points above the Unicode maximum of 0x10FFFF.
@@ -728,14 +908,14 @@ C<UTF8_CHECK_ONLY> is also specified.)
 
 It is now deprecated to have very high code points (above C<IV_MAX> on the
 platforms) and this function will raise a deprecation warning for these (unless
-such warnings are turned off).  This value, is typically 0x7FFF_FFFF (2**31 -1)
+such warnings are turned off).  This value is typically 0x7FFF_FFFF (2**31 -1)
 in a 32-bit word.
 
 Code points above 0x7FFF_FFFF (2**31 - 1) were never specified in any standard,
 so using them is more problematic than other above-Unicode code points.  Perl
 invented an extension to UTF-8 to represent the ones above 2**36-1, so it is
 likely that non-Perl languages will not be able to read files that contain
-these that written by the perl interpreter; nor would Perl understand files
+these; nor would Perl understand files
 written by something that uses a different extension.  For these reasons, there
 is a separate set of flags that can warn and/or disallow these extremely high
 code points, even if other above-Unicode ones are accepted.  These are the
@@ -761,27 +941,145 @@ use and those yet to be assigned, are never considered malformed and never
 warn.
 
 =cut
+
+Also implemented as a macro in utf8.h
 */
 
 UV
-Perl_utf8n_to_uvchr(pTHX_ const U8 *s, STRLEN curlen, STRLEN *retlen, U32 flags)
+Perl_utf8n_to_uvchr(pTHX_ const U8 *s,
+                          STRLEN curlen,
+                          STRLEN *retlen,
+                          const 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 */
+    PERL_ARGS_ASSERT_UTF8N_TO_UVCHR;
 
-    const char* const malformed_text = "Malformed UTF-8 character";
+    return utf8n_to_uvchr_error(s, curlen, retlen, flags, NULL);
+}
 
-    PERL_ARGS_ASSERT_UTF8N_TO_UVCHR;
+/*
+
+=for apidoc utf8n_to_uvchr_error
+
+THIS FUNCTION SHOULD BE USED IN ONLY VERY SPECIALIZED CIRCUMSTANCES.
+Most code should use L</utf8_to_uvchr_buf>() rather than call this directly.
+
+This function is for code that needs to know what the precise malformation(s)
+are when an error is found.
+
+It is like C<L</utf8n_to_uvchr>> but it takes an extra parameter placed after
+all the others, C<errors>.  If this parameter is 0, this function behaves
+identically to C<L</utf8n_to_uvchr>>.  Otherwise, C<errors> should be a pointer
+to a C<U32> variable, which this function sets to indicate any errors found.
+Upon return, if C<*errors> is 0, there were no errors found.  Otherwise,
+C<*errors> is the bit-wise C<OR> of the bits described in the list below.  Some
+of these bits will be set if a malformation is found, even if the input
+C<flags> parameter indicates that the given malformation is allowed; those
+exceptions are noted:
+
+=over 4
+
+=item C<UTF8_GOT_ABOVE_31_BIT>
+
+The code point represented by the input UTF-8 sequence occupies more than 31
+bits.
+This bit is set only if the input C<flags> parameter contains either the
+C<UTF8_DISALLOW_ABOVE_31_BIT> or the C<UTF8_WARN_ABOVE_31_BIT> flags.
+
+=item C<UTF8_GOT_CONTINUATION>
+
+The input sequence was malformed in that the first byte was a a UTF-8
+continuation byte.
+
+=item C<UTF8_GOT_EMPTY>
+
+The input C<curlen> parameter was 0.
+
+=item C<UTF8_GOT_LONG>
+
+The input sequence was malformed in that there is some other sequence that
+evaluates to the same code point, but that sequence is shorter than this one.
+
+=item C<UTF8_GOT_NONCHAR>
+
+The code point represented by the input UTF-8 sequence is for a Unicode
+non-character code point.
+This bit is set only if the input C<flags> parameter contains either the
+C<UTF8_DISALLOW_NONCHAR> or the C<UTF8_WARN_NONCHAR> flags.
+
+=item C<UTF8_GOT_NON_CONTINUATION>
+
+The input sequence was malformed in that a non-continuation type byte was found
+in a position where only a continuation type one should be.
+
+=item C<UTF8_GOT_OVERFLOW>
+
+The input sequence was malformed in that it is for a code point that is not
+representable in the number of bits available in a UV on the current platform.
+
+=item C<UTF8_GOT_SHORT>
+
+The input sequence was malformed in that C<curlen> is smaller than required for
+a complete sequence.  In other words, the input is for a partial character
+sequence.
+
+=item C<UTF8_GOT_SUPER>
+
+The input sequence was malformed in that it is for a non-Unicode code point;
+that is, one above the legal Unicode maximum.
+This bit is set only if the input C<flags> parameter contains either the
+C<UTF8_DISALLOW_SUPER> or the C<UTF8_WARN_SUPER> flags.
+
+=item C<UTF8_GOT_SURROGATE>
+
+The input sequence was malformed in that it is for a -Unicode UTF-16 surrogate
+code point.
+This bit is set only if the input C<flags> parameter contains either the
+C<UTF8_DISALLOW_SURROGATE> or the C<UTF8_WARN_SURROGATE> flags.
+
+=back
+
+To do your own error handling, call this function with the C<UTF8_CHECK_ONLY>
+flag to suppress any warnings, and then examine the C<*errors> return.
+
+=cut
+*/
+
+UV
+Perl_utf8n_to_uvchr_error(pTHX_ const U8 *s,
+                                STRLEN curlen,
+                                STRLEN *retlen,
+                                const U32 flags,
+                                U32 * errors)
+{
+    const U8 * const s0 = s;
+    U8 * send = NULL;           /* (initialized to silence compilers' wrong
+                                   warning) */
+    U32 possible_problems = 0;  /* A bit is set here for each potential problem
+                                   found as we go along */
+    UV uv = *s;
+    STRLEN expectlen   = 0;     /* How long should this sequence be?
+                                   (initialized to silence compilers' wrong
+                                   warning) */
+    STRLEN avail_len   = 0;     /* When input is too short, gives what that is */
+    U32 discard_errors = 0;     /* Used to save branches when 'errors' is NULL;
+                                   this gets set and discarded */
+
+    /* The below are used only if there is both an overlong malformation and a
+     * too short one.  Otherwise the first two are set to 's0' and 'send', and
+     * the third not used at all */
+    U8 * adjusted_s0 = (U8 *) s0;
+    U8 * adjusted_send = NULL;  /* (Initialized to silence compilers' wrong
+                                   warning) */
+    UV uv_so_far = 0;   /* (Initialized to silence compilers' wrong warning) */
+
+    PERL_ARGS_ASSERT_UTF8N_TO_UVCHR_ERROR;
+
+    if (errors) {
+        *errors = 0;
+    }
+    else {
+        errors = &discard_errors;
+    }
 
     /* 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
@@ -801,21 +1099,20 @@ Perl_utf8n_to_uvchr(pTHX_ const U8 *s, STRLEN curlen, STRLEN *retlen, U32 flags)
      * 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 */
+     * sequence and process the rest, inappropriately.
+     *
+     * Some possible input sequences are malformed in more than one way.  This
+     * function goes to lengths to try to find all of them.  This is necessary
+     * for correctness, as the inputs may allow one malformation but not
+     * another, and if we abandon searching for others after finding the
+     * allowed one, we could allow in something that shouldn't have been.
+     */
 
-    /* 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;
+        possible_problems |= UTF8_GOT_EMPTY;
+        curlen = 0;
+        uv = UNICODE_REPLACEMENT;
+       goto ready_to_handle_errors;
     }
 
     expectlen = UTF8SKIP(s);
@@ -835,134 +1132,130 @@ Perl_utf8n_to_uvchr(pTHX_ const U8 *s, STRLEN curlen, STRLEN *retlen, U32 flags)
 
     /* 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;
+       possible_problems |= UTF8_GOT_CONTINUATION;
+        curlen = 1;
+        uv = UNICODE_REPLACEMENT;
+       goto ready_to_handle_errors;
     }
 
     /* Here is not a continuation byte, nor an invariant.  The only thing left
-     * is a start byte (possibly for an overlong) */
+     * is a start byte (possibly for an overlong).  (We can't use UTF8_IS_START
+     * because it excludes start bytes like \xC0 that always lead to
+     * overlongs.) */
 
     /* Convert to I8 on EBCDIC (no-op on ASCII), then 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 = NATIVE_UTF8_TO_I8(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);
+    /* Setup the loop end point, making sure to not look past the end of the
+     * input string, and flag it as too short if the size isn't big enough. */
+    send = (U8*) s0;
+    if (UNLIKELY(curlen < expectlen)) {
+        possible_problems |= UTF8_GOT_SHORT;
+        avail_len = curlen;
+        send += curlen;
+    }
+    else {
+        send += expectlen;
+    }
+    adjusted_send = send;
 
+    /* Now, loop through the remaining bytes in the character's sequence,
+     * accumulating each into the working value as we go. */
     for (s = s0 + 1; s < send; s++) {
        if (LIKELY(UTF8_IS_CONTINUATION(*s))) {
-           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 */
-           }
            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;
-       }
+            continue;
+        }
+
+        /* Here, found a non-continuation before processing all expected bytes.
+         * This byte indicates the beginning of a new character, so quit, even
+         * if allowing this malformation. */
+        possible_problems |= UTF8_GOT_NON_CONTINUATION;
+        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;
-       }
-    }
+    /* A convenience macro that matches either of the too-short conditions.  */
+#   define UTF8_GOT_TOO_SHORT (UTF8_GOT_SHORT|UTF8_GOT_NON_CONTINUATION)
+
+    if (UNLIKELY(possible_problems & UTF8_GOT_TOO_SHORT)) {
+        uv_so_far = uv;
+        uv = UNICODE_REPLACEMENT;
+    }
+
+    /* Note that there are two types of too-short malformation.  One is when
+     * there is actual wrong data before the normal termination of the
+     * sequence.  The other is that the sequence wasn't complete before the end
+     * of the data we are allowed to look at, based on the input 'curlen'.
+     * This means that we were passed data for a partial character, but it is
+     * valid as far as we saw.  The other is definitely invalid.  This
+     * distinction could be important to a caller, so the two types are kept
+     * separate. */
+
+    /* Check for overflow */
+    if (UNLIKELY(does_utf8_overflow(s0, send))) {
+        possible_problems |= UTF8_GOT_OVERFLOW;
+        uv = UNICODE_REPLACEMENT;
+    }
+
+    /* Check for overlong.  If no problems so far, 'uv' is the correct code
+     * point value.  Simply see if it is expressible in fewer bytes.  Otherwise
+     * we must look at the UTF-8 byte sequence itself to see if it is for an
+     * overlong */
+    if (     (   LIKELY(! possible_problems)
+              && UNLIKELY(expectlen > (STRLEN) OFFUNISKIP(uv)))
+        || (   UNLIKELY(  possible_problems)
+            && (   UNLIKELY(! UTF8_IS_START(*s0))
+                || (   curlen > 1
+                    && UNLIKELY(is_utf8_overlong_given_start_byte_ok(s0,
+                                                                send - s0))))))
+    {
+        possible_problems |= UTF8_GOT_LONG;
+
+        if (UNLIKELY(possible_problems & UTF8_GOT_TOO_SHORT)) {
+            UV min_uv = uv_so_far;
+            STRLEN i;
+
+            /* Here, the input is both overlong and is missing some trailing
+             * bytes.  There is no single code point it could be for, but there
+             * may be enough information present to determine if what we have
+             * so far is for an unallowed code point, such as for a surrogate.
+             * The code below has the intelligence to determine this, but just
+             * for non-overlong UTF-8 sequences.  What we do here is calculate
+             * the smallest code point the input could represent if there were
+             * no too short malformation.  Then we compute and save the UTF-8
+             * for that, which is what the code below looks at instead of the
+             * raw input.  It turns out that the smallest such code point is
+             * all we need. */
+            for (i = curlen; i < expectlen; i++) {
+                min_uv = UTF8_ACCUMULATE(min_uv,
+                                     I8_TO_NATIVE_UTF8(UTF_CONTINUATION_MARK));
+            }
 
-    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;
+            Newx(adjusted_s0, OFFUNISKIP(min_uv) + 1, U8);
+            SAVEFREEPV((U8 *) adjusted_s0);    /* Needed because we may not get
+                                                  to free it ourselves if
+                                                  warnings are made fatal */
+            adjusted_send = uvoffuni_to_utf8_flags(adjusted_s0, min_uv, 0);
+        }
     }
 
-    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;
-    }
+    /* Now check that the input isn't for a problematic code point not allowed
+     * by the input parameters. */
+                                              /* isn't problematic if < this */
+    if (   (   (   LIKELY(! possible_problems) && uv >= UNICODE_SURROGATE_FIRST)
+            || (   UNLIKELY(possible_problems)
 
-    /* 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 */
+                          /* if overflow, we know without looking further
+                           * precisely which of the problematic types it is,
+                           * and we deal with those in the overflow handling
+                           * code */
+                && LIKELY(! (possible_problems & UTF8_GOT_OVERFLOW))
+                && isUTF8_POSSIBLY_PROBLEMATIC(*adjusted_s0)))
        && ((flags & ( UTF8_DISALLOW_NONCHAR
                       |UTF8_DISALLOW_SURROGATE
                       |UTF8_DISALLOW_SUPER
@@ -971,153 +1264,459 @@ Perl_utf8n_to_uvchr(pTHX_ const U8 *s, STRLEN curlen, STRLEN *retlen, U32 flags)
                       |UTF8_WARN_SURROGATE
                       |UTF8_WARN_SUPER
                       |UTF8_WARN_ABOVE_31_BIT))
+                   /* In case of a malformation, 'uv' is not valid, and has
+                    * been changed to something in the Unicode range.
+                    * Currently we don't output a deprecation message if there
+                    * is already a malformation, so we don't have to special
+                    * case the test immediately below */
             || (   UNLIKELY(uv > MAX_NON_DEPRECATED_CP)
                 && ckWARN_d(WARN_DEPRECATED))))
     {
-       if (UNICODE_IS_SURROGATE(uv)) {
+        /* If there were no malformations, or the only malformation is an
+         * overlong, 'uv' is valid */
+        if (LIKELY(! (possible_problems & ~UTF8_GOT_LONG))) {
+            if (UNLIKELY(UNICODE_IS_SURROGATE(uv))) {
+                possible_problems |= UTF8_GOT_SURROGATE;
+            }
+            else if (UNLIKELY(uv > PERL_UNICODE_MAX)) {
+                possible_problems |= UTF8_GOT_SUPER;
+            }
+            else if (UNLIKELY(UNICODE_IS_NONCHAR(uv))) {
+                possible_problems |= UTF8_GOT_NONCHAR;
+            }
+        }
+        else {  /* Otherwise, need to look at the source UTF-8, possibly
+                   adjusted to be non-overlong */
+
+            if (UNLIKELY(NATIVE_UTF8_TO_I8(*adjusted_s0)
+                                >= FIRST_START_BYTE_THAT_IS_DEFINITELY_SUPER))
+            {
+                possible_problems |= UTF8_GOT_SUPER;
+            }
+            else if (curlen > 1) {
+                if (UNLIKELY(IS_UTF8_2_BYTE_SUPER(
+                                      NATIVE_UTF8_TO_I8(*adjusted_s0),
+                                      NATIVE_UTF8_TO_I8(*(adjusted_s0 + 1)))))
+                {
+                    possible_problems |= UTF8_GOT_SUPER;
+                }
+                else if (UNLIKELY(IS_UTF8_2_BYTE_SURROGATE(
+                                      NATIVE_UTF8_TO_I8(*adjusted_s0),
+                                      NATIVE_UTF8_TO_I8(*(adjusted_s0 + 1)))))
+                {
+                    possible_problems |= UTF8_GOT_SURROGATE;
+                }
+            }
+
+            /* We need a complete well-formed UTF-8 character to discern
+             * non-characters, so can't look for them here */
+        }
+    }
+
+  ready_to_handle_errors:
+
+    /* At this point:
+     * curlen               contains the number of bytes in the sequence that
+     *                      this call should advance the input by.
+     * avail_len            gives the available number of bytes passed in, but
+     *                      only if this is less than the expected number of
+     *                      bytes, based on the code point's start byte.
+     * possible_problems'   is 0 if there weren't any problems; otherwise a bit
+     *                      is set in it for each potential problem found.
+     * uv                   contains the code point the input sequence
+     *                      represents; or if there is a problem that prevents
+     *                      a well-defined value from being computed, it is
+     *                      some subsitute value, typically the REPLACEMENT
+     *                      CHARACTER.
+     * s0                   points to the first byte of the character
+     * send                 points to just after where that (potentially
+     *                      partial) character ends
+     * adjusted_s0          normally is the same as s0, but in case of an
+     *                      overlong for which the UTF-8 matters below, it is
+     *                      the first byte of the shortest form representation
+     *                      of the input.
+     * adjusted_send        normally is the same as 'send', but if adjusted_s0
+     *                      is set to something other than s0, this points one
+     *                      beyond its end
+     */
+
+    if (UNLIKELY(possible_problems)) {
+        bool disallowed = FALSE;
+        const U32 orig_problems = possible_problems;
+
+        while (possible_problems) { /* Handle each possible problem */
+            UV pack_warn = 0;
+            char * message = NULL;
+
+            /* Each 'if' clause handles one problem.  They are ordered so that
+             * the first ones' messages will be displayed before the later
+             * ones; this is kinda in decreasing severity order */
+            if (possible_problems & UTF8_GOT_OVERFLOW) {
+
+                /* Overflow means also got a super and above 31 bits, but we
+                 * handle all three cases here */
+                possible_problems
+                  &= ~(UTF8_GOT_OVERFLOW|UTF8_GOT_SUPER|UTF8_GOT_ABOVE_31_BIT);
+                *errors |= UTF8_GOT_OVERFLOW;
+
+                /* But the API says we flag all errors found */
+                if (flags & (UTF8_WARN_SUPER|UTF8_DISALLOW_SUPER)) {
+                    *errors |= UTF8_GOT_SUPER;
+                }
+                if (flags
+                        & (UTF8_WARN_ABOVE_31_BIT|UTF8_DISALLOW_ABOVE_31_BIT))
+                {
+                    *errors |= UTF8_GOT_ABOVE_31_BIT;
+                }
+
+                /* Disallow if any of the three categories say to */
+                if ( ! (flags & UTF8_ALLOW_OVERFLOW)
+                    || (flags & ( UTF8_DISALLOW_SUPER
+                                 |UTF8_DISALLOW_ABOVE_31_BIT)))
+                {
+                    disallowed = TRUE;
+                }
+
+
+                /* Likewise, warn if any say to, plus if deprecation warnings
+                 * are on, because this code point is above IV_MAX */
+                if (  ckWARN_d(WARN_DEPRECATED)
+                    || ! (flags & UTF8_ALLOW_OVERFLOW)
+                    ||   (flags & (UTF8_WARN_SUPER|UTF8_WARN_ABOVE_31_BIT)))
+                {
+
+                    /* The warnings code explicitly says it doesn't handle the
+                     * case of packWARN2 and two categories which have
+                     * parent-child relationship.  Even if it works now to
+                     * raise the warning if either is enabled, it wouldn't
+                     * necessarily do so in the future.  We output (only) the
+                     * most dire warning*/
+                    if (! (flags & UTF8_CHECK_ONLY)) {
+                        if (ckWARN_d(WARN_UTF8)) {
+                            pack_warn = packWARN(WARN_UTF8);
+                        }
+                        else if (ckWARN_d(WARN_NON_UNICODE)) {
+                            pack_warn = packWARN(WARN_NON_UNICODE);
+                        }
+                        if (pack_warn) {
+                            message = Perl_form(aTHX_ "%s: %s (overflows)",
+                                            malformed_text,
+                                            _byte_dump_string(s0, send - s0));
+                        }
+                    }
+                }
+            }
+            else if (possible_problems & UTF8_GOT_EMPTY) {
+                possible_problems &= ~UTF8_GOT_EMPTY;
+                *errors |= UTF8_GOT_EMPTY;
+
+                if (! (flags & UTF8_ALLOW_EMPTY)) {
+
+                    /* This so-called malformation is now treated as a bug in
+                     * the caller.  If you have nothing to decode, skip calling
+                     * this function */
+                    assert(0);
+
+                    disallowed = TRUE;
+                    if (ckWARN_d(WARN_UTF8) && ! (flags & UTF8_CHECK_ONLY)) {
+                        pack_warn = packWARN(WARN_UTF8);
+                        message = Perl_form(aTHX_ "%s (empty string)",
+                                                   malformed_text);
+                    }
+                }
+            }
+            else if (possible_problems & UTF8_GOT_CONTINUATION) {
+                possible_problems &= ~UTF8_GOT_CONTINUATION;
+                *errors |= UTF8_GOT_CONTINUATION;
+
+                if (! (flags & UTF8_ALLOW_CONTINUATION)) {
+                    disallowed = TRUE;
+                    if (ckWARN_d(WARN_UTF8) && ! (flags & UTF8_CHECK_ONLY)) {
+                        pack_warn = packWARN(WARN_UTF8);
+                        message = Perl_form(aTHX_
+                                "%s: %s (unexpected continuation byte 0x%02x,"
+                                " with no preceding start byte)",
+                                malformed_text,
+                                _byte_dump_string(s0, 1), *s0);
+                    }
+                }
+            }
+            else if (possible_problems & UTF8_GOT_SHORT) {
+                possible_problems &= ~UTF8_GOT_SHORT;
+                *errors |= UTF8_GOT_SHORT;
+
+                if (! (flags & UTF8_ALLOW_SHORT)) {
+                    disallowed = TRUE;
+                    if (ckWARN_d(WARN_UTF8) && ! (flags & UTF8_CHECK_ONLY)) {
+                        pack_warn = packWARN(WARN_UTF8);
+                        message = Perl_form(aTHX_
+                                "%s: %s (too short; %d byte%s available, need %d)",
+                                malformed_text,
+                                _byte_dump_string(s0, send - s0),
+                                (int)avail_len,
+                                avail_len == 1 ? "" : "s",
+                                (int)expectlen);
+                    }
+                }
 
-            /* 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);
-           }
+            }
+            else if (possible_problems & UTF8_GOT_NON_CONTINUATION) {
+                possible_problems &= ~UTF8_GOT_NON_CONTINUATION;
+                *errors |= UTF8_GOT_NON_CONTINUATION;
+
+                if (! (flags & UTF8_ALLOW_NON_CONTINUATION)) {
+                    disallowed = TRUE;
+                    if (ckWARN_d(WARN_UTF8) && ! (flags & UTF8_CHECK_ONLY)) {
+
+                        /* If we don't know for sure that the input length is
+                         * valid, avoid as much as possible reading past the
+                         * end of the buffer */
+                        int printlen = (flags & _UTF8_NO_CONFIDENCE_IN_CURLEN)
+                                       ? s - s0
+                                       : send - s0;
+                        pack_warn = packWARN(WARN_UTF8);
+                        message = Perl_form(aTHX_ "%s",
+                            unexpected_non_continuation_text(s0,
+                                                            printlen,
+                                                            s - s0,
+                                                            (int) expectlen));
+                    }
+                }
+            }
+            else if (possible_problems & UTF8_GOT_LONG) {
+                possible_problems &= ~UTF8_GOT_LONG;
+                *errors |= UTF8_GOT_LONG;
 
-            /* The maximum code point ever specified by a standard was
-             * 2**31 - 1.  Anything larger than that is a Perl extension that
-             * very well may not be understood by other applications (including
-             * earlier perl versions on EBCDIC platforms).  We test for these
-             * after the regular SUPER ones, and before possibly bailing out,
-             * so that the slightly more dire warning will override the regular
-             * one. */
-            if (   (flags & (UTF8_WARN_ABOVE_31_BIT
-                            |UTF8_WARN_SUPER
-                            |UTF8_DISALLOW_ABOVE_31_BIT))
-                && UNLIKELY(is_utf8_cp_above_31_bits(s0, send)))
-            {
-                if (  ! (flags & UTF8_CHECK_ONLY)
-                    &&  (flags & (UTF8_WARN_ABOVE_31_BIT|UTF8_WARN_SUPER))
-                    &&  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_ALLOW_LONG) {
+
+                    /* We don't allow the actual overlong value, unless the
+                     * special extra bit is also set */
+                    if (! (flags & (   UTF8_ALLOW_LONG_AND_ITS_VALUE
+                                    & ~UTF8_ALLOW_LONG)))
+                    {
+                        uv = UNICODE_REPLACEMENT;
+                    }
                 }
-                if (flags & UTF8_DISALLOW_ABOVE_31_BIT) {
-                    goto disallowed;
+                else {
+                    disallowed = TRUE;
+
+                    if (ckWARN_d(WARN_UTF8) && ! (flags & UTF8_CHECK_ONLY)) {
+                        pack_warn = packWARN(WARN_UTF8);
+
+                        /* These error types cause 'uv' to be something that
+                         * isn't what was intended, so can't use it in the
+                         * message.  The other error types either can't
+                         * generate an overlong, or else the 'uv' is valid */
+                        if (orig_problems &
+                                        (UTF8_GOT_TOO_SHORT|UTF8_GOT_OVERFLOW))
+                        {
+                            message = Perl_form(aTHX_
+                                    "%s: %s (any UTF-8 sequence that starts"
+                                    " with \"%s\" is overlong which can and"
+                                    " should be represented with a"
+                                    " different, shorter sequence)",
+                                    malformed_text,
+                                    _byte_dump_string(s0, send - s0),
+                                    _byte_dump_string(s0, curlen));
+                        }
+                        else {
+                            U8 tmpbuf[UTF8_MAXBYTES+1];
+                            const U8 * const e = uvoffuni_to_utf8_flags(tmpbuf,
+                                                                        uv, 0);
+                            message = Perl_form(aTHX_
+                                "%s: %s (overlong; instead use %s to represent"
+                                " U+%0*" UVXf ")",
+                                malformed_text,
+                                _byte_dump_string(s0, send - s0),
+                                _byte_dump_string(tmpbuf, e - tmpbuf),
+                                ((uv < 256) ? 2 : 4), /* Field width of 2 for
+                                                         small code points */
+                                uv);
+                        }
+                    }
                 }
             }
+            else if (possible_problems & UTF8_GOT_SURROGATE) {
+                possible_problems &= ~UTF8_GOT_SURROGATE;
 
-           if (flags & UTF8_DISALLOW_SUPER) {
-               goto disallowed;
-           }
+                if (flags & UTF8_WARN_SURROGATE) {
+                    *errors |= UTF8_GOT_SURROGATE;
 
-            /* The deprecated warning overrides any non-deprecated one */
-            if (UNLIKELY(uv > MAX_NON_DEPRECATED_CP) && ckWARN_d(WARN_DEPRECATED))
-            {
-                sv = sv_2mortal(Perl_newSVpvf(aTHX_ cp_above_legal_max,
-                                              uv, MAX_NON_DEPRECATED_CP));
-                pack_warn = packWARN(WARN_DEPRECATED);
+                    if (   ! (flags & UTF8_CHECK_ONLY)
+                        && ckWARN_d(WARN_SURROGATE))
+                    {
+                        pack_warn = packWARN(WARN_SURROGATE);
+
+                        /* These are the only errors that can occur with a
+                        * surrogate when the 'uv' isn't valid */
+                        if (orig_problems & UTF8_GOT_TOO_SHORT) {
+                            message = Perl_form(aTHX_
+                                    "UTF-16 surrogate (any UTF-8 sequence that"
+                                    " starts with \"%s\" is for a surrogate)",
+                                    _byte_dump_string(s0, curlen));
+                        }
+                        else {
+                            message = Perl_form(aTHX_
+                                            "UTF-16 surrogate U+%04" UVXf, uv);
+                        }
+                    }
+                }
+
+                if (flags & UTF8_DISALLOW_SURROGATE) {
+                    disallowed = TRUE;
+                    *errors |= UTF8_GOT_SURROGATE;
+                }
             }
-       }
-       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 not recommended for open interchange", uv));
-               pack_warn = packWARN(WARN_NONCHAR);
-           }
-           if (flags & UTF8_DISALLOW_NONCHAR) {
-               goto disallowed;
-           }
-       }
+            else if (possible_problems & UTF8_GOT_SUPER) {
+                possible_problems &= ~UTF8_GOT_SUPER;
 
-       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;
-       }
+                if (flags & UTF8_WARN_SUPER) {
+                    *errors |= UTF8_GOT_SUPER;
 
-       /* Here, this is not considered a malformed character, so drop through
-        * to return it */
-    }
+                    if (   ! (flags & UTF8_CHECK_ONLY)
+                        && ckWARN_d(WARN_NON_UNICODE))
+                    {
+                        pack_warn = packWARN(WARN_NON_UNICODE);
+
+                        if (orig_problems & UTF8_GOT_TOO_SHORT) {
+                            message = Perl_form(aTHX_
+                                    "Any UTF-8 sequence that starts with"
+                                    " \"%s\" is for a non-Unicode code point,"
+                                    " may not be portable",
+                                    _byte_dump_string(s0, curlen));
+                        }
+                        else {
+                            message = Perl_form(aTHX_
+                                                "Code point 0x%04" UVXf " is not"
+                                                " Unicode, may not be portable",
+                                                uv);
+                        }
+                    }
+                }
 
-    return UNI_TO_NATIVE(uv);
+                /* The maximum code point ever specified by a standard was
+                 * 2**31 - 1.  Anything larger than that is a Perl extension
+                 * that very well may not be understood by other applications
+                 * (including earlier perl versions on EBCDIC platforms).  We
+                 * test for these after the regular SUPER ones, and before
+                 * possibly bailing out, so that the slightly more dire warning
+                 * will override the regular one. */
+                if (   (flags & (UTF8_WARN_ABOVE_31_BIT
+                                |UTF8_WARN_SUPER
+                                |UTF8_DISALLOW_ABOVE_31_BIT))
+                    && (   (   UNLIKELY(orig_problems & UTF8_GOT_TOO_SHORT)
+                            && UNLIKELY(is_utf8_cp_above_31_bits(
+                                                                adjusted_s0,
+                                                                adjusted_send)))
+                        || (   LIKELY(! (orig_problems & UTF8_GOT_TOO_SHORT))
+                            && UNLIKELY(UNICODE_IS_ABOVE_31_BIT(uv)))))
+                {
+                    if (  ! (flags & UTF8_CHECK_ONLY)
+                        &&  (flags & (UTF8_WARN_ABOVE_31_BIT|UTF8_WARN_SUPER))
+                        &&  ckWARN_d(WARN_UTF8))
+                    {
+                        pack_warn = packWARN(WARN_UTF8);
+
+                        if (orig_problems & UTF8_GOT_TOO_SHORT) {
+                            message = Perl_form(aTHX_
+                                        "Any UTF-8 sequence that starts with"
+                                        " \"%s\" is for a non-Unicode code"
+                                        " point, and is not portable",
+                                        _byte_dump_string(s0, curlen));
+                        }
+                        else {
+                            message = Perl_form(aTHX_
+                                        "Code point 0x%" UVXf " is not Unicode,"
+                                        " and not portable",
+                                         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>.
-     */
+                    if (flags & ( UTF8_WARN_ABOVE_31_BIT
+                                 |UTF8_DISALLOW_ABOVE_31_BIT))
+                    {
+                        *errors |= UTF8_GOT_ABOVE_31_BIT;
 
-  malformed:
+                        if (flags & UTF8_DISALLOW_ABOVE_31_BIT) {
+                            disallowed = TRUE;
+                        }
+                    }
+                }
 
-    if (sv && ckWARN_d(WARN_UTF8)) {
-       pack_warn = packWARN(WARN_UTF8);
-    }
+                if (flags & UTF8_DISALLOW_SUPER) {
+                    *errors |= UTF8_GOT_SUPER;
+                    disallowed = TRUE;
+                }
 
-  disallowed:
+                /* The deprecated warning overrides any non-deprecated one.  If
+                 * there are other problems, a deprecation message is not
+                 * really helpful, so don't bother to raise it in that case.
+                 * This also keeps the code from having to handle the case
+                 * where 'uv' is not valid. */
+                if (   ! (orig_problems
+                                    & (UTF8_GOT_TOO_SHORT|UTF8_GOT_OVERFLOW))
+                    && UNLIKELY(uv > MAX_NON_DEPRECATED_CP)
+                    && ckWARN_d(WARN_DEPRECATED))
+                {
+                    message = Perl_form(aTHX_ cp_above_legal_max,
+                                              uv, MAX_NON_DEPRECATED_CP);
+                    pack_warn = packWARN(WARN_DEPRECATED);
+                }
+            }
+            else if (possible_problems & UTF8_GOT_NONCHAR) {
+                possible_problems &= ~UTF8_GOT_NONCHAR;
 
-    if (flags & UTF8_CHECK_ONLY) {
-       if (retlen)
-           *retlen = ((STRLEN) -1);
-       return 0;
-    }
+                if (flags & UTF8_WARN_NONCHAR) {
+                    *errors |= UTF8_GOT_NONCHAR;
 
-  do_warn:
+                    if (  ! (flags & UTF8_CHECK_ONLY)
+                        && ckWARN_d(WARN_NONCHAR))
+                    {
+                        /* The code above should have guaranteed that we don't
+                         * get here with errors other than overlong */
+                        assert (! (orig_problems
+                                        & ~(UTF8_GOT_LONG|UTF8_GOT_NONCHAR)));
+
+                        pack_warn = packWARN(WARN_NONCHAR);
+                        message = Perl_form(aTHX_ "Unicode non-character"
+                                                " U+%04" UVXf " is not recommended"
+                                                " for open interchange", uv);
+                    }
+                }
 
-    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 (flags & UTF8_DISALLOW_NONCHAR) {
+                    disallowed = TRUE;
+                    *errors |= UTF8_GOT_NONCHAR;
+                }
+            } /* End of looking through the possible flags */
+
+            /* Display the message (if any) for the problem being handled in
+             * this iteration of the loop */
+            if (message) {
+                if (PL_op)
+                    Perl_warner(aTHX_ pack_warn, "%s in %s", message,
+                                                 OP_DESC(PL_op));
+                else
+                    Perl_warner(aTHX_ pack_warn, "%s", message);
+            }
+        }   /* End of 'while (possible_problems)' */
 
-       if (PL_op)
-           Perl_warner(aTHX_ pack_warn, "%s in %s", string,  OP_DESC(PL_op));
-       else
-           Perl_warner(aTHX_ pack_warn, "%s", string);
-    }
+        /* Since there was a possible problem, the returned length may need to
+         * be changed from the one stored at the beginning of this function.
+         * Instead of trying to figure out if that's needed, just do it. */
+        if (retlen) {
+            *retlen = curlen;
+        }
 
-    if (retlen) {
-       *retlen = curlen;
+        if (disallowed) {
+            if (flags & UTF8_CHECK_ONLY && retlen) {
+                *retlen = ((STRLEN) -1);
+            }
+            return 0;
+        }
     }
 
-    return outlier_ret;
+    return UNI_TO_NATIVE(uv);
 }
 
 /*
@@ -1152,7 +1751,7 @@ 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);
+                     ckWARN_d(WARN_UTF8) ? 0 : UTF8_ALLOW_ANY);
 }
 
 /* This is marked as deprecated
@@ -1268,14 +1867,12 @@ Perl_bytes_cmp_utf8(pTHX_ const U8 *b, STRLEN blen, const U8 *u, STRLEN ulen)
                    if (UTF8_IS_CONTINUATION(c1)) {
                        c = EIGHT_BIT_UTF8_TO_NATIVE(c, c1);
                    } else {
+                        /* diag_listed_as: Malformed UTF-8 character%s */
                        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) : "");
+                                    "%s %s%s",
+                                    unexpected_non_continuation_text(u - 1, 2, 1, 2),
+                                    PL_op ? " in " : "",
+                                    PL_op ? OP_DESC(PL_op) : "");
                        return -2;
                    }
                } else {
@@ -1466,7 +2063,7 @@ Perl_utf16_to_utf8(pTHX_ U8* p, U8* d, I32 bytelen, I32 *newlen)
     PERL_ARGS_ASSERT_UTF16_TO_UTF8;
 
     if (bytelen & 1)
-       Perl_croak(aTHX_ "panic: utf16_to_utf8: odd bytelen %"UVuf, (UV)bytelen);
+       Perl_croak(aTHX_ "panic: utf16_to_utf8: odd bytelen %" UVuf, (UV)bytelen);
 
     pend = p + bytelen;
 
@@ -1540,7 +2137,7 @@ Perl_utf16_to_utf8_reversed(pTHX_ U8* p, U8* d, I32 bytelen, I32 *newlen)
     PERL_ARGS_ASSERT_UTF16_TO_UTF8_REVERSED;
 
     if (bytelen & 1)
-       Perl_croak(aTHX_ "panic: utf16_to_utf8_reversed: odd bytelen %"UVuf,
+       Perl_croak(aTHX_ "panic: utf16_to_utf8_reversed: odd bytelen %" UVuf,
                   (UV)bytelen);
 
     while (s < send) {
@@ -1557,7 +2154,7 @@ 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);
+    return _is_utf8_FOO_with_len(classnum, tmpbuf, tmpbuf + sizeof(tmpbuf));
 }
 
 /* Internal function so we can deprecate the external one, and call
@@ -1578,7 +2175,7 @@ Perl__is_uni_perl_idcont(pTHX_ UV c)
 {
     U8 tmpbuf[UTF8_MAXBYTES+1];
     uvchr_to_utf8(tmpbuf, c);
-    return _is_utf8_perl_idcont(tmpbuf);
+    return _is_utf8_perl_idcont_with_len(tmpbuf, tmpbuf + sizeof(tmpbuf));
 }
 
 bool
@@ -1586,7 +2183,7 @@ Perl__is_uni_perl_idstart(pTHX_ UV c)
 {
     U8 tmpbuf[UTF8_MAXBYTES+1];
     uvchr_to_utf8(tmpbuf, c);
-    return _is_utf8_perl_idstart(tmpbuf);
+    return _is_utf8_perl_idstart_with_len(tmpbuf, tmpbuf + sizeof(tmpbuf));
 }
 
 UV
@@ -1696,7 +2293,7 @@ Perl_to_uni_title(pTHX_ UV c, U8* p, STRLEN *lenp)
 }
 
 STATIC U8
-S_to_lower_latin1(const U8 c, U8* p, STRLEN *lenp)
+S_to_lower_latin1(const U8 c, U8* p, STRLEN *lenp, const char dummy)
 {
     /* We have the latin1-range values compiled into the core, so just use
      * those, converting the result to UTF-8.  Since the result is always just
@@ -1704,6 +2301,8 @@ S_to_lower_latin1(const U8 c, U8* p, STRLEN *lenp)
 
     U8 converted = toLOWER_LATIN1(c);
 
+    PERL_UNUSED_ARG(dummy);
+
     if (p != NULL) {
        if (NATIVE_BYTE_IS_INVARIANT(converted)) {
            *p = converted;
@@ -1726,7 +2325,7 @@ 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);
+       return to_lower_latin1((U8) c, p, lenp, 0 /* 0 is a dummy arg */ );
     }
 
     uvchr_to_utf8(p, c);
@@ -1829,13 +2428,13 @@ Perl__to_uni_fold_flags(pTHX_ UV c, U8* p, STRLEN *lenp, U8 flags)
        uvchr_to_utf8(p, c);
        return CALL_FOLD_CASE(c, p, p, lenp, flags & FOLD_FLAGS_FULL);
     }
-    else {  /* Otherwise, _to_utf8_fold_flags has the intelligence to deal with
+    else {  /* Otherwise, _toFOLD_utf8_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);
+       return _toFOLD_utf8_flags(utf8_c, p, lenp, flags);
     }
 }
 
@@ -1864,16 +2463,46 @@ S_is_utf8_common(pTHX_ const U8 *const p, SV **swash,
      * 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;
+        _force_out_malformed_utf8_message(p, p + UTF8SKIP(p),
+                                          _UTF8_NO_CONFIDENCE_IN_CURLEN,
+                                          1 /* Die */ );
+        NOT_REACHED; /* NOTREACHED */
+    }
+
+    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;
+}
+
+PERL_STATIC_INLINE bool
+S_is_utf8_common_with_len(pTHX_ const U8 *const p, const U8 * const e, SV **swash,
+                         const char *const swashname, SV* const invlist)
+{
+    /* returns a boolean giving whether or not the UTF8-encoded character that
+     * starts at <p>, and extending no further than <e - 1> 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.
+     */
+
+    PERL_ARGS_ASSERT_IS_UTF8_COMMON_WITH_LEN;
+
+    if (! isUTF8_CHAR(p, e)) {
+        _force_out_malformed_utf8_message(p, e, 0, 1);
+        NOT_REACHED; /* NOTREACHED */
     }
+
     if (!*swash) {
         U8 flags = _CORE_SWASH_INIT_ACCEPT_INVLIST;
         *swash = _core_swash_init("utf8",
@@ -1888,30 +2517,154 @@ S_is_utf8_common(pTHX_ const U8 *const p, SV **swash,
     return swash_fetch(*swash, p, TRUE) != 0;
 }
 
+STATIC void
+S_warn_on_first_deprecated_use(pTHX_ const char * const name,
+                                     const char * const alternative,
+                                     const bool use_locale,
+                                     const char * const file,
+                                     const unsigned line)
+{
+    const char * key;
+
+    PERL_ARGS_ASSERT_WARN_ON_FIRST_DEPRECATED_USE;
+
+    if (ckWARN_d(WARN_DEPRECATED)) {
+
+        key = Perl_form(aTHX_ "%s;%d;%s;%d", name, use_locale, file, line);
+       if (! hv_fetch(PL_seen_deprecated_macro, key, strlen(key), 0)) {
+            if (! PL_seen_deprecated_macro) {
+                PL_seen_deprecated_macro = newHV();
+            }
+            if (! hv_store(PL_seen_deprecated_macro, key,
+                           strlen(key), &PL_sv_undef, 0))
+            {
+               Perl_croak(aTHX_ "panic: hv_store() unexpectedly failed");
+            }
+
+                Perl_warner(aTHX_ WARN_DEPRECATED,
+                            "In %s, line %d, starting in Perl v5.30, %s() will"
+                            " require an additional parameter.  Avoid this"
+                            " message by converting to use %s().\n",
+                            file, line, name, alternative);
+        }
+    }
+}
+
 bool
-Perl__is_utf8_FOO(pTHX_ const U8 classnum, const U8 *p)
+Perl__is_utf8_FOO(pTHX_       U8   classnum,
+                        const U8   *p,
+                        const char * const name,
+                        const char * const alternative,
+                        const bool use_utf8,
+                        const bool use_locale,
+                        const char * const file,
+                        const unsigned line)
 {
     PERL_ARGS_ASSERT__IS_UTF8_FOO;
 
+    warn_on_first_deprecated_use(name, alternative, use_locale, file, line);
+
+    if (use_utf8 && UTF8_IS_ABOVE_LATIN1(*p)) {
+        SV * invlist;
+
+        switch (classnum) {
+            case _CC_WORDCHAR:
+            case _CC_DIGIT:
+            case _CC_ALPHA:
+            case _CC_LOWER:
+            case _CC_UPPER:
+            case _CC_PUNCT:
+            case _CC_PRINT:
+            case _CC_ALPHANUMERIC:
+            case _CC_GRAPH:
+            case _CC_CASED:
+
+                return is_utf8_common(p,
+                                      &PL_utf8_swash_ptrs[classnum],
+                                      swash_property_names[classnum],
+                                      PL_XPosix_ptrs[classnum]);
+
+            case _CC_SPACE:
+                return is_XPERLSPACE_high(p);
+            case _CC_BLANK:
+                return is_HORIZWS_high(p);
+            case _CC_XDIGIT:
+                return is_XDIGIT_high(p);
+            case _CC_CNTRL:
+                return 0;
+            case _CC_ASCII:
+                return 0;
+            case _CC_VERTSPACE:
+                return is_VERTWS_high(p);
+            case _CC_IDFIRST:
+                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);
+            case _CC_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);
+        }
+    }
+
+    /* idcont is the same as wordchar below 256 */
+    if (classnum == _CC_IDCONT) {
+        classnum = _CC_WORDCHAR;
+    }
+    else if (classnum == _CC_IDFIRST) {
+        if (*p == '_') {
+            return TRUE;
+        }
+        classnum = _CC_ALPHA;
+    }
+
+    if (! use_locale) {
+        if (! use_utf8 || UTF8_IS_INVARIANT(*p)) {
+            return _generic_isCC(*p, classnum);
+        }
+
+        return _generic_isCC(EIGHT_BIT_UTF8_TO_NATIVE(*p, *(p + 1 )), classnum);
+    }
+    else {
+        if (! use_utf8 || UTF8_IS_INVARIANT(*p)) {
+            return isFOO_lc(classnum, *p);
+        }
+
+        return isFOO_lc(classnum, EIGHT_BIT_UTF8_TO_NATIVE(*p, *(p + 1 )));
+    }
+
+    NOT_REACHED; /* NOTREACHED */
+}
+
+bool
+Perl__is_utf8_FOO_with_len(pTHX_ const U8 classnum, const U8 *p,
+                                                            const U8 * const e)
+{
+    PERL_ARGS_ASSERT__IS_UTF8_FOO_WITH_LEN;
+
     assert(classnum < _FIRST_NON_SWASH_CC);
 
-    return is_utf8_common(p,
-                          &PL_utf8_swash_ptrs[classnum],
-                          swash_property_names[classnum],
-                          PL_XPosix_ptrs[classnum]);
+    return is_utf8_common_with_len(p,
+                                   e,
+                                   &PL_utf8_swash_ptrs[classnum],
+                                   swash_property_names[classnum],
+                                   PL_XPosix_ptrs[classnum]);
 }
 
 bool
-Perl__is_utf8_perl_idstart(pTHX_ const U8 *p)
+Perl__is_utf8_perl_idstart_with_len(pTHX_ const U8 *p, const U8 * const e)
 {
     SV* invlist = NULL;
 
-    PERL_ARGS_ASSERT__IS_UTF8_PERL_IDSTART;
+    PERL_ARGS_ASSERT__IS_UTF8_PERL_IDSTART_WITH_LEN;
 
     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);
+    return is_utf8_common_with_len(p, e, &PL_utf8_perl_idstart,
+                                      "_Perl_IDStart", invlist);
 }
 
 bool
@@ -1925,16 +2678,17 @@ Perl__is_utf8_xidstart(pTHX_ const U8 *p)
 }
 
 bool
-Perl__is_utf8_perl_idcont(pTHX_ const U8 *p)
+Perl__is_utf8_perl_idcont_with_len(pTHX_ const U8 *p, const U8 * const e)
 {
     SV* invlist = NULL;
 
-    PERL_ARGS_ASSERT__IS_UTF8_PERL_IDCONT;
+    PERL_ARGS_ASSERT__IS_UTF8_PERL_IDCONT_WITH_LEN;
 
     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);
+    return is_utf8_common_with_len(p, e, &PL_utf8_perl_idcont,
+                                   "_Perl_IDCont", invlist);
 }
 
 bool
@@ -2066,7 +2820,7 @@ S__to_utf8_case(pTHX_ const UV uv1, const U8 *p, U8* ustrp, STRLEN *lenp,
                     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);
+                            "Operation \"%s\" returns its argument for UTF-16 surrogate U+%04" UVXf, desc, uv1);
                     }
                     goto cases_to_self;
                 }
@@ -2088,7 +2842,7 @@ S__to_utf8_case(pTHX_ const UV uv1, const U8 *p, U8* ustrp, STRLEN *lenp,
                     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);
+                            "Operation \"%s\" returns its argument for non-Unicode code point 0x%04" UVXf, desc, uv1);
                     }
                     goto cases_to_self;
                 }
@@ -2226,8 +2980,8 @@ S_check_locale_boundary_crossing(pTHX_ const U8* const p, const UV result, U8* c
 
     /* 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"}\".",
+                           "Can't do %s(\"\\x{%" UVXf "}\") on non-UTF-8 locale; "
+                           "resolved to \"\\x{%" UVXf "}\".",
                            OP_DESC(PL_op),
                            original,
                            original);
@@ -2235,6 +2989,89 @@ S_check_locale_boundary_crossing(pTHX_ const U8* const p, const UV result, U8* c
     return original;
 }
 
+/* The process for changing the case is essentially the same for the four case
+ * change types, except there are complications for folding.  Otherwise the
+ * difference is only which case to change to.  To make sure that they all do
+ * the same thing, the bodies of the functions are extracted out into the
+ * following two macros.  The functions are written with the same variable
+ * names, and these are known and used inside these macros.  It would be
+ * better, of course, to have inline functions to do it, but since different
+ * macros are called, depending on which case is being changed to, this is not
+ * feasible in C (to khw's knowledge).  Two macros are created so that the fold
+ * function can start with the common start macro, then finish with its special
+ * handling; while the other three cases can just use the common end macro.
+ *
+ * The algorithm is to use the proper (passed in) macro or function to change
+ * the case for code points that are below 256.  The macro is used if using
+ * locale rules for the case change; the function if not.  If the code point is
+ * above 255, it is computed from the input UTF-8, and another macro is called
+ * to do the conversion.  If necessary, the output is converted to UTF-8.  If
+ * using a locale, we have to check that the change did not cross the 255/256
+ * boundary, see check_locale_boundary_crossing() for further details.
+ *
+ * The macros are split with the correct case change for the below-256 case
+ * stored into 'result', and in the middle of an else clause for the above-255
+ * case.  At that point in the 'else', 'result' is not the final result, but is
+ * the input code point calculated from the UTF-8.  The fold code needs to
+ * realize all this and take it from there.
+ *
+ * If you read the two macros as sequential, it's easier to understand what's
+ * going on. */
+#define CASE_CHANGE_BODY_START(locale_flags, LC_L1_change_macro, L1_func,    \
+                               L1_func_extra_param)                          \
+    if (flags & (locale_flags)) {                                            \
+        /* Treat a UTF-8 locale as not being in locale at all */             \
+        if (IN_UTF8_CTYPE_LOCALE) {                                          \
+            flags &= ~(locale_flags);                                        \
+        }                                                                    \
+        else {                                                               \
+            _CHECK_AND_WARN_PROBLEMATIC_LOCALE;                              \
+        }                                                                    \
+    }                                                                        \
+                                                                             \
+    if (UTF8_IS_INVARIANT(*p)) {                                             \
+        if (flags & (locale_flags)) {                                        \
+            result = LC_L1_change_macro(*p);                                 \
+        }                                                                    \
+        else {                                                               \
+            return L1_func(*p, ustrp, lenp, L1_func_extra_param);            \
+        }                                                                    \
+    }                                                                        \
+    else if UTF8_IS_DOWNGRADEABLE_START(*p) {                                \
+        if (flags & (locale_flags)) {                                        \
+            result = LC_L1_change_macro(EIGHT_BIT_UTF8_TO_NATIVE(*p,         \
+                                                                 *(p+1)));   \
+        }                                                                    \
+        else {                                                               \
+            return L1_func(EIGHT_BIT_UTF8_TO_NATIVE(*p, *(p+1)),             \
+                           ustrp, lenp,  L1_func_extra_param);               \
+        }                                                                    \
+    }                                                                        \
+    else {  /* malformed UTF-8 */                                            \
+        result = valid_utf8_to_uvchr(p, NULL);                               \
+
+#define CASE_CHANGE_BODY_END(locale_flags, change_macro)                     \
+        result = change_macro(result, p, ustrp, lenp);                       \
+                                                                             \
+        if (flags & (locale_flags)) {                                        \
+            result = check_locale_boundary_crossing(p, result, ustrp, lenp); \
+        }                                                                    \
+        return result;                                                       \
+    }                                                                        \
+                                                                             \
+    /* Here, used locale rules.  Convert back to UTF-8 */                    \
+    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_upper
 
@@ -2253,55 +3090,10 @@ Perl__to_utf8_upper_flags(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp, bool flags
 
     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 = EIGHT_BIT_UTF8_TO_NATIVE(*p, *(p+1));
-           result = toUPPER_LC(c);
-       }
-       else {
-           return _to_upper_title_latin1(EIGHT_BIT_UTF8_TO_NATIVE(*p, *(p+1)),
-                                         ustrp, lenp, 'S');
-       }
-    }
-    else {  /* UTF-8, ord above 255 */
-       result = CALL_UPPER_CASE(valid_utf8_to_uvchr(p, NULL), p, ustrp, lenp);
-
-       if (flags) {
-           result = check_locale_boundary_crossing(p, result, ustrp, lenp);
-       }
-       return result;
-    }
-
-    /* Here, used locale rules.  Convert back to UTF-8 */
-    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;
+    /* ~0 makes anything non-zero in 'flags' mean we are using locale rules */
+    /* 2nd char of uc(U+DF) is 'S' */
+    CASE_CHANGE_BODY_START(~0, toUPPER_LC, _to_upper_title_latin1, 'S');
+    CASE_CHANGE_BODY_END  (~0, CALL_UPPER_CASE);
 }
 
 /*
@@ -2324,55 +3116,9 @@ Perl__to_utf8_title_flags(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp, bool flags
 
     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 = EIGHT_BIT_UTF8_TO_NATIVE(*p, *(p+1));
-           result = toUPPER_LC(c);
-       }
-       else {
-           return _to_upper_title_latin1(EIGHT_BIT_UTF8_TO_NATIVE(*p, *(p+1)),
-                                         ustrp, lenp, 's');
-       }
-    }
-    else {  /* UTF-8, ord above 255 */
-       result = CALL_TITLE_CASE(valid_utf8_to_uvchr(p, NULL), p, ustrp, lenp);
-
-       if (flags) {
-           result = check_locale_boundary_crossing(p, result, ustrp, lenp);
-       }
-       return result;
-    }
-
-    /* Here, used locale rules.  Convert back to UTF-8 */
-    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;
+    /* 2nd char of ucfirst(U+DF) is 's' */
+    CASE_CHANGE_BODY_START(~0, toUPPER_LC, _to_upper_title_latin1, 's');
+    CASE_CHANGE_BODY_END  (~0, CALL_TITLE_CASE);
 }
 
 /*
@@ -2394,56 +3140,8 @@ Perl__to_utf8_lower_flags(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp, bool flags
 
     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 = EIGHT_BIT_UTF8_TO_NATIVE(*p, *(p+1));
-           result = toLOWER_LC(c);
-       }
-       else {
-           return to_lower_latin1(EIGHT_BIT_UTF8_TO_NATIVE(*p, *(p+1)),
-                                  ustrp, lenp);
-       }
-    }
-    else {  /* UTF-8, ord above 255 */
-       result = CALL_LOWER_CASE(valid_utf8_to_uvchr(p, NULL), p, ustrp, lenp);
-
-       if (flags) {
-           result = check_locale_boundary_crossing(p, result, ustrp, lenp);
-       }
-
-       return result;
-    }
-
-    /* Here, used locale rules.  Convert back to UTF-8 */
-    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;
+    CASE_CHANGE_BODY_START(~0, toLOWER_LC, to_lower_latin1, 0 /* 0 is dummy */)
+    CASE_CHANGE_BODY_END  (~0, CALL_LOWER_CASE)
 }
 
 /*
@@ -2475,38 +3173,10 @@ Perl__to_utf8_fold_flags(pTHX_ const U8 *p, U8* ustrp, STRLEN *lenp, U8 flags)
 
     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;
-        }
-    }
+    CASE_CHANGE_BODY_START(FOLD_FLAGS_LOCALE, toFOLD_LC, _to_fold_latin1,
+                 ((flags) & (FOLD_FLAGS_FULL | FOLD_FLAGS_NOMIX_ASCII)));
 
-    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 = EIGHT_BIT_UTF8_TO_NATIVE(*p, *(p+1));
-           result = toFOLD_LC(c);
-       }
-       else {
-           return _to_fold_latin1(EIGHT_BIT_UTF8_TO_NATIVE(*p, *(p+1)),
-                            ustrp, lenp,
-                            flags & (FOLD_FLAGS_FULL | FOLD_FLAGS_NOMIX_ASCII));
-       }
-    }
-    else {  /* UTF-8, ord above 255 */
-       result = CALL_FOLD_CASE(valid_utf8_to_uvchr(p, NULL), p, ustrp, lenp, flags & FOLD_FLAGS_FULL);
+       result = CALL_FOLD_CASE(result, p, ustrp, lenp, flags & FOLD_FLAGS_FULL);
 
        if (flags & FOLD_FLAGS_LOCALE) {
 
@@ -2841,7 +3511,7 @@ Perl__core_swash_init(pTHX_ const char* pkg, const char* name, SV *listsv, I32 m
                     CORE_SWASH_INIT_RETURN(NULL);
                }
                Perl_croak(aTHX_
-                          "Can't find Unicode property definition \"%"SVf"\"",
+                          "Can't find Unicode property definition \"%" SVf "\"",
                           SVfARG(retval));
                 NOT_REACHED; /* NOTREACHED */
             }
@@ -2901,6 +3571,7 @@ Perl__core_swash_init(pTHX_ const char* pkg, const char* name, SV *listsv, I32 m
                /* Add the passed-in inversion list, which invalidates the one
                 * already stored in the swash */
                invlist_in_swash_is_valid = FALSE;
+                SvREADONLY_off(swash_invlist);  /* Turned on again below */
                _invlist_union(invlist, swash_invlist, &swash_invlist);
            }
            else {
@@ -2930,6 +3601,7 @@ Perl__core_swash_init(pTHX_ const char* pkg, const char* name, SV *listsv, I32 m
            else SvREFCNT_inc_simple_void_NN(swash_invlist);
        }
 
+        /* The result is immutable.  Forbid attempts to change it. */
         SvREADONLY_on(swash_invlist);
 
         /* Use the inversion list stand-alone if small enough */
@@ -3110,7 +3782,7 @@ Perl_swash_fetch(pTHX_ SV *swash, const U8 *ptr, bool do_utf8)
            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=%p, tmps=%p, slen=%" UVuf ", needents=%" UVuf,
                           svp, tmps, (UV)slen, (UV)needents);
        }
 
@@ -3143,7 +3815,7 @@ Perl_swash_fetch(pTHX_ SV *swash, const U8 *ptr, bool do_utf8)
             ((UV) tmps[off + 3]);
     }
     Perl_croak(aTHX_ "panic: swash_fetch got swatch of unexpected bit width, "
-              "slen=%"UVuf", needents=%"UVuf, (UV)slen, (UV)needents);
+              "slen=%" UVuf ", needents=%" UVuf, (UV)slen, (UV)needents);
     NORETURN_FUNCTION_END;
 }
 
@@ -3300,7 +3972,7 @@ S_swatch_get(pTHX_ SV* swash, UV start, UV span)
     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,
+       Perl_croak(aTHX_ "panic: swatch_get doesn't expect bits %" UVuf,
                                                 (UV)bits);
     }
 
@@ -3479,7 +4151,7 @@ S_swatch_get(pTHX_ SV* swash, UV start, UV span)
        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);
+                      "bits=%" UVuf ", otherbits=%" UVuf, (UV)bits, (UV)otherbits);
 
        /* The "other" swatch must be destroyed after. */
        other = swatch_get(*othersvp, start, span);
@@ -3492,7 +4164,7 @@ S_swatch_get(pTHX_ SV* swash, UV start, UV span)
        if (bits == 1 && otherbits == 1) {
            if (slen != olen)
                Perl_croak(aTHX_ "panic: swatch_get found swatch length "
-                          "mismatch, slen=%"UVuf", olen=%"UVuf,
+                          "mismatch, slen=%" UVuf ", olen=%" UVuf,
                           (UV)slen, (UV)olen);
 
            switch (opc) {
@@ -3654,7 +4326,7 @@ Perl__swash_inversion_hash(pTHX_ SV* const swash)
 
     /* 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,
+       Perl_croak(aTHX_ "panic: swash_inversion_hash doesn't expect bits %" UVuf,
                                                 (UV)bits);
     }
 
@@ -3683,7 +4355,7 @@ Perl__swash_inversion_hash(pTHX_ SV* const swash)
                           "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)));*/
+           /*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 UTF-8) that map to
@@ -3762,7 +4434,7 @@ Perl__swash_inversion_hash(pTHX_ SV* const swash)
                                        (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));*/
+                       /*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));*/
                    }
                }
            }
@@ -3836,7 +4508,7 @@ Perl__swash_inversion_hash(pTHX_ SV* const swash)
                }
                entry = *entryp;
                uv = SvUV(entry);
-               /*DEBUG_U(PerlIO_printf(Perl_debug_log, "list for %"UVXf" contains %"UVXf"\n", val, uv));*/
+               /*DEBUG_U(PerlIO_printf(Perl_debug_log, "list for %" UVXf " contains %" UVXf "\n", val, uv));*/
                if (uv == val) {
                    found_key = TRUE;
                }
@@ -3854,14 +4526,14 @@ Perl__swash_inversion_hash(pTHX_ SV* const swash)
            /* 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));*/
+               /*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));*/
+               /*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
@@ -3969,7 +4641,7 @@ Perl__swash_to_invlist(pTHX_ SV* const swash)
             /* 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);
+                    Perl_croak(aTHX_ "panic: Expecting %" UVuf " more elements than available", elements);
                 }
                 while (isSPACE(*l)) l++;
                 if (!grok_atoUV((const char *)l, other_elements_ptr++, &after_atou)) {
@@ -4068,7 +4740,7 @@ Perl__swash_to_invlist(pTHX_ SV* const swash)
 
        if (bits != otherbits || bits != 1) {
            Perl_croak(aTHX_ "panic: _swash_to_invlist only operates on boolean "
-                      "properties, bits=%"UVuf", otherbits=%"UVuf,
+                      "properties, bits=%" UVuf ", otherbits=%" UVuf,
                       (UV)bits, (UV)otherbits);
        }
 
@@ -4147,7 +4819,6 @@ Perl_check_utf8_print(pTHX_ const U8* s, const STRLEN len)
            return FALSE;
        }
        if (UNLIKELY(isUTF8_POSSIBLY_PROBLEMATIC(*s))) {
-           STRLEN char_len;
            if (UNLIKELY(UTF8_IS_SUPER(s, e))) {
                 if (   ckWARN_d(WARN_NON_UNICODE)
                     || (   ckWARN_d(WARN_DEPRECATED)
@@ -4167,7 +4838,7 @@ Perl_check_utf8_print(pTHX_ const U8* s, const STRLEN len)
 #endif
                 )) {
                     /* A side effect of this function will be to warn */
-                    (void) utf8n_to_uvchr(s, e - s, &char_len, UTF8_WARN_SUPER);
+                    (void) utf8n_to_uvchr(s, e - s, NULL, UTF8_WARN_SUPER);
                     ok = FALSE;
                 }
            }
@@ -4176,15 +4847,15 @@ Perl_check_utf8_print(pTHX_ const U8* s, const STRLEN len)
                     /* This has a different warning than the one the called
                      * function would output, so can't just call it, unlike we
                      * do for the non-chars and above-unicodes */
-                   UV uv = utf8_to_uvchr_buf(s, e, &char_len);
+                   UV uv = utf8_to_uvchr_buf(s, e, NULL);
                    Perl_warner(aTHX_ packWARN(WARN_SURROGATE),
-                       "Unicode surrogate U+%04"UVXf" is illegal in UTF-8", uv);
+                       "Unicode surrogate U+%04" UVXf " is illegal in UTF-8", uv);
                    ok = FALSE;
                }
            }
            else if (UNLIKELY(UTF8_IS_NONCHAR(s, e)) && (ckWARN_d(WARN_NONCHAR))) {
                 /* A side effect of this function will be to warn */
-                (void) utf8n_to_uvchr(s, e - s, &char_len, UTF8_WARN_NONCHAR);
+                (void) utf8n_to_uvchr(s, e - s, NULL, UTF8_WARN_NONCHAR);
                ok = FALSE;
            }
        }
@@ -4221,7 +4892,7 @@ Perl_pv_uni_display(pTHX_ SV *dsv, const U8 *spv, STRLEN len, STRLEN pvlim, UV f
 
     PERL_ARGS_ASSERT_PV_UNI_DISPLAY;
 
-    sv_setpvs(dsv, "");
+    SvPVCLEAR(dsv);
     SvUTF8_off(dsv);
     for (s = (const char *)spv, e = s + len; s < e; s += UTF8SKIP(s)) {
         UV u;
@@ -4267,7 +4938,7 @@ Perl_pv_uni_display(pTHX_ SV *dsv, const U8 *spv, STRLEN len, STRLEN pvlim, UV f
             }
         }
         if (!ok)
-            Perl_sv_catpvf(aTHX_ dsv, "\\x{%"UVxf"}", u);
+            Perl_sv_catpvf(aTHX_ dsv, "\\x{%" UVxf "}", u);
     }
     if (truncated)
         sv_catpvs(dsv, "...");
@@ -4480,7 +5151,7 @@ Perl_foldEQ_utf8_flags(pTHX_ const char *s1, char **pe1, UV l1, bool u1, const c
                     *foldbuf1 = toFOLD(*p1);
                 }
                 else if (u1) {
-                    _to_utf8_fold_flags(p1, foldbuf1, &n1, flags_for_folder);
+                    _toFOLD_utf8_flags(p1, foldbuf1, &n1, flags_for_folder);
                 }
                 else {  /* Not UTF-8, get UTF-8 fold */
                     _to_uni_fold_flags(*p1, foldbuf1, &n1, flags_for_folder);
@@ -4504,7 +5175,7 @@ Perl_foldEQ_utf8_flags(pTHX_ const char *s1, char **pe1, UV l1, bool u1, const c
                     *foldbuf2 = toFOLD(*p2);
                 }
                 else if (u2) {
-                    _to_utf8_fold_flags(p2, foldbuf2, &n2, flags_for_folder);
+                    _toFOLD_utf8_flags(p2, foldbuf2, &n2, flags_for_folder);
                 }
                 else {
                     _to_uni_fold_flags(*p2, foldbuf2, &n2, flags_for_folder);