utf8.c: Move a static function to inline.h

This is in preparation for it being called from outside utf8.c.  It is
renamed to have a leading underscore to emphasize its private nature

1 files changed, 31 insertions, 0 deletions

diff --git a/inline.h b/inline.h
index 615c2e39aa..34d9b3b866 100644
--- a/inline.h
+++ b/inline.h
@@ -238,6 +238,37 @@ S_isALNUM_lazy(pTHX_ const char* p)
     return isALNUM_lazy_if(p,1);
 }
 
+/*
+Tests if the first C<len> bytes of string C<s> form a valid UTF-8
+character.  Note that an INVARIANT (i.e. ASCII on non-EBCDIC) character is a
+valid UTF-8 character.  The number of bytes in the UTF-8 character
+will be returned if it is valid, otherwise 0.
+
+This is the "slow" version as opposed to the "fast" version which is
+the "unrolled" IS_UTF8_CHAR().  E.g. for t/uni/class.t the speed
+difference is a factor of 2 to 3.  For lengths (UTF8SKIP(s)) of four
+or less you should use the IS_UTF8_CHAR(), for lengths of five or more
+you should use the _slow().  In practice this means that the _slow()
+will be used very rarely, since the maximum Unicode code point (as of
+Unicode 4.1) is U+10FFFF, which encodes in UTF-8 to four bytes.  Only
+the "Perl extended UTF-8" (e.g, the infamous 'v-strings') will encode into
+five bytes or more.
+
+=cut */
+PERL_STATIC_INLINE STRLEN
+S__is_utf8_char_slow(const U8 *s, const STRLEN len)
+{
+    dTHX;   /* The function called below requires thread context */
+
+    STRLEN actual_len;
+
+    PERL_ARGS_ASSERT__IS_UTF8_CHAR_SLOW;
+
+    utf8n_to_uvchr(s, len, &actual_len, UTF8_CHECK_ONLY);
+
+    return (actual_len == (STRLEN) -1) ? 0 : actual_len;
+}
+
 /* ------------------------------- perl.h ----------------------------- */
 
 /*