lib/libc/amd64/string: implement strsep() through strcspn()

The strsep() function is basically strcspn() with extra steps.
On amd64, we now have an optimised implementation of strcspn(),
so instead of implementing the inner loop manually, just call
into the optimised routine.

Sponsored by:	The FreeBSD Foundation
Tested by:	developers@, exp-run
Approved by:	mjg
MFC after:	1 month
MFC to:		stable/14
PR:		275785
Differential Revision:	https://reviews.freebsd.org/D42346

2 files changed, 58 insertions, 0 deletions

diff --git a/lib/libc/amd64/string/Makefile.inc b/lib/libc/amd64/string/Makefile.inc
index 2baa631fb3fa..ee396f98eccc 100644
--- a/lib/libc/amd64/string/Makefile.inc
+++ b/lib/libc/amd64/string/Makefile.inc
@@ -17,6 +17,7 @@ MDSRCS+= \
 	strnlen.c \
 	strpbrk.c \
 	strrchr.S \
+	strsep.c \
 	strspn.S \
 	timingsafe_bcmp.S \
 	timingsafe_memcmp.S
diff --git a/lib/libc/amd64/string/strsep.c b/lib/libc/amd64/string/strsep.c
new file mode 100644
index 000000000000..9fda56d7e135
--- /dev/null
+++ b/lib/libc/amd64/string/strsep.c
@@ -0,0 +1,57 @@
+/*-
+ * 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>
+
+size_t __strcspn(const char *, const char *);
+
+/*
+ * We have a fast strcspn() on amd64.  Use it over a direct
+ * implementation of strsep for better performance.
+ */
+char *
+strsep(char **stringp, const char *delim)
+{
+	size_t n;
+	char *s;
+
+	s = *stringp;
+	if (s == NULL)
+		return (NULL);
+
+	n = __strcspn(s, delim);
+	if (s[n] == '\0')
+		*stringp = NULL;
+	else {
+		s[n] = '\0';
+		*stringp = s + n + 1;
+	}
+
+	return (s);
+}