wcsmbs: optimize wcsnlen

This patch rewrites wcsnlen using wmemchr.  The generic wmemchr
already uses the strategy (loop unrolling and tail handling) and
by using it it allows architectures that have optimized wmemchr
(s390 and x86_64) to optimize wcsnlen as well.

Checked on x86_64-linux-gnu.

	* wcsmbs/wcsnlen.c (__wcsnlen): Rewrite using wmemchr.

2 files changed, 6 insertions, 18 deletions

diff --git a/ChangeLog b/ChangeLog
index 97e70aa..9ab66cf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,7 @@
 2019-02-27  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
+	* wcsmbs/wcsnlen.c (__wcsnlen): Rewrite using wmemchr.
+
 	* wcsmbs/wcsncpy.c (__wcsncpy): Rewrite using wcsnlen, wmemset, and
 	wmemcpy.
 
diff --git a/wcsmbs/wcsnlen.c b/wcsmbs/wcsnlen.c
index f3d5fc1..d38c7e4 100644
--- a/wcsmbs/wcsnlen.c
+++ b/wcsmbs/wcsnlen.c
@@ -26,24 +26,10 @@
 size_t
 __wcsnlen (const wchar_t *s, size_t maxlen)
 {
-  size_t len = 0;
-
-  while (maxlen > 0 && s[len] != L'\0')
-    {
-      ++len;
-      if (--maxlen == 0 || s[len] == L'\0')
-	return len;
-      ++len;
-      if (--maxlen == 0 || s[len] == L'\0')
-	return len;
-      ++len;
-      if (--maxlen == 0 || s[len] == L'\0')
-	return len;
-      ++len;
-      --maxlen;
-    }
-
-  return len;
+  const wchar_t *ret = __wmemchr (s, L'\0', maxlen);
+  if (ret)
+    maxlen = ret - s;
+  return maxlen;
 }
 #ifndef WCSNLEN
 weak_alias (__wcsnlen, wcsnlen)