This patch improves strncat performance by using strlen. Strlen has a fast C implementation, so

this
will improve performance even on targets which don't have an optimized strlen. It is about twice
as
fast as the original strncat in bench-strncat.

2 files changed, 6 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index f73c55e..40e294b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2014-10-24  Wilco Dijkstra  <wdijkstr@arm.com>
 
+	* string/strncat.c (strncat): Improve performance by using strlen.
+
+2014-10-24  Wilco Dijkstra  <wdijkstr@arm.com>
+
 	* string/strcat.c (strcat): Improve performance by using strlen/strcpy.
 
 2014-10-24  Wilco Dijkstra  <wdijkstr@arm.com>
diff --git a/string/strncat.c b/string/strncat.c
index 7ac4456..6d29114 100644
--- a/string/strncat.c
+++ b/string/strncat.c
@@ -33,13 +33,11 @@ STRNCAT (char *s1, const char *s2, size_t n)
   char *s = s1;
 
   /* Find the end of S1.  */
-  do
-    c = *s1++;
-  while (c != '\0');
+  s1 += strlen (s1);
 
   /* Make S1 point before next character, so we can increment
      it while memory is read (wins on pipelined cpus).  */
-  s1 -= 2;
+  s1 -= 1;
 
   if (n >= 4)
     {