[newlib-cygwin] Modify strnstr.c.

[Corinna Vinschen <corinna@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=f22054c94d3f77ba834d55123ffa9fe4aef6f93c

commit f22054c94d3f77ba834d55123ffa9fe4aef6f93c
Author: Sichen Zhao <1473996754@qq.com>
Date:   Wed Aug 30 11:03:56 2017 +0800

    Modify strnstr.c.

Diff:
---
 newlib/libc/string/strnstr.c | 65 +++++++-------------------------------------
 1 file changed, 10 insertions(+), 55 deletions(-)

diff --git a/newlib/libc/string/strnstr.c b/newlib/libc/string/strnstr.c
index da5e5bd..05d86ee 100644
--- a/newlib/libc/string/strnstr.c
+++ b/newlib/libc/string/strnstr.c
@@ -1,42 +1,5 @@
-/*-
- * Copyright (c) 2001 Mike Barcroft <mike@FreeBSD.org>
- * Copyright (c) 1990, 1993
- *	The Regents of the University of California.  All rights reserved.
- *
- * This code is derived from software contributed to Berkeley by
- * Chris Torek.
- *
- * 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.
- * 3. Neither the name of the University nor the names of its contributors
- *    may be used to endorse or promote products derived from this software
- *    without specific prior written permission.
- *
- * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
- */
-
-#if defined(LIBC_SCCS) && !defined(lint)
-static char sccsid[] = "@(#)strstr.c	8.1 (Berkeley) 6/4/93";
-#endif /* LIBC_SCCS and not lint */
-#include <sys/cdefs.h>
-__FBSDID("$FreeBSD: head/lib/libc/string/strnstr.c 251069 2013-05-28 20:57:40Z emaste $");
-
+#undef __STRICT_ANSI__
+#include <_ansi.h>
 #include <string.h>
 
 /*
@@ -44,22 +7,14 @@ __FBSDID("$FreeBSD: head/lib/libc/string/strnstr.c 251069 2013-05-28 20:57:40Z e
  * first slen characters of s.
  */
 char *
-strnstr(const char *s, const char *find, size_t slen)
+strnstr(const char *haystack, const char *needle, size_t haystack_len)
 {
-	char c, sc;
-	size_t len;
+  size_t needle_len = strnlen(needle, haystack_len);
 
-	if ((c = *find++) != '\0') {
-		len = strlen(find);
-		do {
-			do {
-				if (slen-- < 1 || (sc = *s++) == '\0')
-					return (NULL);
-			} while (sc != c);
-			if (len > slen)
-				return (NULL);
-		} while (strncmp(s, find, len) != 0);
-		s--;
-	}
-	return ((char *)s);
+  if (needle_len < haystack_len || !needle[needle_len]) {
+    char *x = memmem(haystack, haystack_len, needle, needle_len);
+    if (x && !memchr(haystack, 0, x - haystack))
+      return x;
+  }
+  return NULL;
 }