(PREV_CHAR_BOUNDARY): Make it work from within a char's byte sequence.

(AT_CHAR_BOUNDARY): New macro.

1 files changed, 17 insertions, 5 deletions

diff --git a/src/charset.h b/src/charset.h
index b7ab4cb8b53..b25a2ffa85a 100644
--- a/src/charset.h
+++ b/src/charset.h
@@ -658,22 +658,34 @@ else
   } while (0)
 
 
-/* If P is after LIMIT, advance P to the previous character boundary.
-   It assumes that P is already at a character boundary of the sane
-   mulitbyte form whose beginning address is LIMIT.  */
+/* If P is after LIMIT, advance P to the previous character boundary.  */
 
 #define PREV_CHAR_BOUNDARY(p, limit)                                    \
   do {                                                                  \
     if ((p) > (limit))                                                  \
       {                                                                 \
         const unsigned char *p0 = (p);                                  \
+        const unsigned char *p_limit = max (limit, p0 - MAX_MULTIBYTE_LENGTH);\
         do {                                                            \
           p0--;                                                         \
-        } while (p0 >= limit && ! CHAR_HEAD_P (*p0));                   \
-        (p) = (BYTES_BY_CHAR_HEAD (*p0) == (p) - p0) ? p0 : (p) - 1;    \
+        } while (p0 >= p_limit && ! CHAR_HEAD_P (*p0));                 \
+        /* If BBCH(*p0) > p-p0, it means we were not on a boundary.  */ \
+        (p) = (BYTES_BY_CHAR_HEAD (*p0) >= (p) - p0) ? p0 : (p) - 1;    \
       }                                                                 \
   } while (0)
 
+#define AT_CHAR_BOUNDARY_P(result, p, limit)    \
+  do {                                          \
+    if (CHAR_HEAD_P (*(p)) || (p) <= limit)     \
+      /* Optimization for the common case. */   \
+      (result) = 1;                             \
+    else                                        \
+      {                                         \
+        const unsigned char *p_aux = (p)+1;     \
+        PREV_CHAR_BOUNDARY (p_aux, limit);      \
+        (result) = (p_aux == (p));              \
+      }                                         \
+} while (0)
 
 #ifdef emacs