Fix UTF-8 auto alignment

diff --git a/expat/lib/xmltok.c b/expat/lib/xmltok.c
index 72058d3c772e11a43319280ba3e7533f0d25091e..4195279536a75dc16d246ca5d68b030d3bb23769 100644 (file)
--- a/expat/lib/xmltok.c
+++ b/expat/lib/xmltok.c
@@ -333,9 +333,34 @@ void
 align_limit_to_full_utf8_characters(const char * from, const char ** fromLimRef)
 {
   const char * fromLim = *fromLimRef;
-  for (; fromLim > from; fromLim--)
-    if (((unsigned char)fromLim[-1] & 0xc0) != 0x80)
+  size_t walked = 0;
+  for (; fromLim > from; fromLim--, walked++) {
+    const unsigned char prev = (unsigned char)fromLim[-1];
+    if ((prev & 0xf8u) == 0xf0u) { /* 4-byte character, lead by 0b11110xxx byte */
+      if (walked + 1 >= 4) {
+        fromLim += 4 - 1;
+        break;
+      } else {
+        walked = 0;
+      }
+    } else if ((prev & 0xf0u) == 0xe0u) { /* 3-byte character, lead by 0b1110xxxx byte */
+      if (walked + 1 >= 3) {
+        fromLim += 3 - 1;
+        break;
+      } else {
+        walked = 0;
+      }
+    } else if ((prev & 0xe0u) == 0xc0u) { /* 2-byte character, lead by 0b110xxxxx byte */
+      if (walked + 1 >= 2) {
+        fromLim += 2 - 1;
+        break;
+      } else {
+        walked = 0;
+      }
+    } else if ((prev & 0x80u) == 0x00u) { /* 1-byte character, matching 0b0xxxxxxx */
       break;
+    }
+  }
   *fromLimRef = fromLim;
 }