Add S_sv_pos_u2b_midway for when we know the utf-8/bytes offsets on

both sides of the desired offset, so could count either way.
Use cached utf-8 length in S_sv_pos_u2b_cached.
Check the results if PL_utf8cache < 0.

p4raw-id: //depot/perl@27573

diff --git a/sv.c b/sv.c
index 27f2b80..69232be 100644 (file)
--- a/sv.c
+++ b/sv.c
@@ -5517,17 +5517,65 @@ S_sv_pos_u2b_forwards(pTHX_ const U8 *const start, const U8 *const send,
     return s - start;
 }
 
+
+static STRLEN
+S_sv_pos_u2b_midway(pTHX_ const U8 *const start, const U8 *send,
+                     STRLEN uoffset, STRLEN uend)
+{
+    STRLEN backw = uend - uoffset;
+    if (uoffset < 2 * backw) {
+       /* The assumption is that going fowards is twice the speed of going
+          forward (that's where the 2 * backw comes from).
+          (The real figure of course depends on the UTF-8 data.)  */
+       return S_sv_pos_u2b_forwards(aTHX_ start, send, uoffset);
+    }
+
+    while (backw--) {
+       send--;
+       while (UTF8_IS_CONTINUATION(*send))
+           send--;
+    }
+    return send - start;
+}
+
 static STRLEN
 S_sv_pos_u2b_cached(pTHX_ SV *sv, MAGIC **mgp, const U8 *const start,
                    const U8 *const send, STRLEN uoffset,
                    STRLEN uoffset0, STRLEN boffset0) {
     STRLEN boffset;
-    if (uoffset >= uoffset0) {
-       boffset = boffset0 + S_sv_pos_u2b_forwards(aTHX_ start + boffset0,
-                                                  send, uoffset - uoffset0);
+    bool found = FALSE;
+
+    if (SvMAGICAL(sv) && !SvREADONLY(sv) && PL_utf8cache
+       && (*mgp = mg_find(sv, PERL_MAGIC_utf8))) {
+       if ((*mgp)->mg_len != -1) {
+           boffset = S_sv_pos_u2b_midway(aTHX_ start, send, uoffset,
+                                         (*mgp)->mg_len);
+           found = TRUE;
+       }
     }
-    else {
-       boffset = S_sv_pos_u2b_forwards(aTHX_ start, send, uoffset);
+
+    if (!found || PL_utf8cache < 0) {
+       STRLEN real_boffset;
+       if (uoffset >= uoffset0) {
+           real_boffset
+               = boffset0 + S_sv_pos_u2b_forwards(aTHX_ start + boffset0,
+                                                  send, uoffset - uoffset0);
+       }
+       else {
+           real_boffset = S_sv_pos_u2b_forwards(aTHX_ start, send, uoffset);
+       }
+       if (found && PL_utf8cache < 0) {
+           if (real_boffset != boffset) {
+               /* Need to turn the assertions off otherwise we may recurse
+                  infinitely while printing error messages.  */
+               SAVEI8(PL_utf8cache);
+               PL_utf8cache = 0;
+               Perl_croak(aTHX_ "panic: sv_pos_u2b_cache cache %"UVf
+                          " real %"UVf" for %"SVf,
+                          (UV) boffset, (UV) real_boffset, sv);
+           }
+       }
+       boffset = real_boffset;
     }
     return boffset;
 }