Bug-fix in Tcl_UtfAtIndex (for TCL_UTF_MAX=4 only). With test-case (in "string totitle") demonstrating the bug.

1 files changed, 8 insertions, 0 deletions

diff --git a/generic/tclUtf.c b/generic/tclUtf.c
index 0d88d36..c08464b 100644
--- a/generic/tclUtf.c
+++ b/generic/tclUtf.c
@@ -762,10 +762,18 @@ Tcl_UtfAtIndex(
     register int index)		/* The position of the desired character. */
 {
     Tcl_UniChar ch = 0;
+    int len = 1;
 
     while (index-- > 0) {
+	len = TclUtfToUniChar(src, &ch);
+	src += len;
+    }
+#if TCL_UTF_MAX == 4
+     if (!len) {
+	/* Index points at character following High Surrogate */
 	src += TclUtfToUniChar(src, &ch);
     }
+#endif
     return src;
 }