lib/libc/amd64/string: implement strnlen(3) trough memchr(3)

Now that we have an optimised memchr(3), we can use it to implement
strnlen(3) with better perofrmance.

Sponsored by:	The FreeBSD Foundation
Approved by:	mjg
MFC after:	1 week
MFC to:		stable/14
Differential Revision:	https://reviews.freebsd.org/D41598

2 files changed, 44 insertions, 1 deletions

diff --git a/lib/libc/amd64/string/Makefile.inc b/lib/libc/amd64/string/Makefile.inc
index 7c6a1f429590..73973a6d69de 100644
--- a/lib/libc/amd64/string/Makefile.inc
+++ b/lib/libc/amd64/string/Makefile.inc
@@ -11,7 +11,8 @@ MDSRCS+= \
 	strcat.S \
 	strchrnul.S \
 	strcmp.S \
+	strcpy.c \
 	strcspn.S \
 	strlen.S \
-	strcpy.c \
+	strnlen.c \
 	strspn.S
diff --git a/lib/libc/amd64/string/strnlen.c b/lib/libc/amd64/string/strnlen.c
new file mode 100644
index 000000000000..9db4ce30dfd4
--- /dev/null
+++ b/lib/libc/amd64/string/strnlen.c
@@ -0,0 +1,42 @@
+/*-
+ * Copyright (c) 2023 The FreeBSD Foundation
+ *
+ * This software was developed by Robert Clausecker <fuz@FreeBSD.org>
+ * under sponsorship from the FreeBSD Foundation.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ''AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE
+ */
+
+#include <sys/cdefs.h>
+#include <string.h>
+
+char *__memchr(const void *, int, size_t);
+
+size_t
+strnlen(const char *s, size_t maxlen)
+{
+	const char *loc;
+
+	loc = __memchr(s, '\0', maxlen);
+
+	return (loc == NULL ? maxlen : (size_t)(loc - s));
+}