1 files changed, 76 insertions, 0 deletions
diff --git a/lib/strstr.c b/lib/strstr.c
new file mode 100644
index 0000000..574f4d5
--- /dev/null
+++ b/lib/strstr.c
@@ -0,0 +1,76 @@
+/* Copyright (C) 1991-1994, 1996-1998, 2000, 2004, 2007-2023 Free Software
+   Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   This file is free software: you can redistribute it and/or modify
+   it under the terms of the GNU Lesser General Public License as
+   published by the Free Software Foundation; either version 2.1 of the
+   License, or (at your option) any later version.
+
+   This file is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+/* This particular implementation was written by Eric Blake, 2008.  */
+
+#ifndef _LIBC
+# include <config.h>
+#endif
+
+/* Specification of strstr.  */
+#include <string.h>
+
+#define RETURN_TYPE char *
+#define AVAILABLE(h, h_l, j, n_l)                       \
+  (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l))     \
+   && ((h_l) = (j) + (n_l)))
+#include "str-two-way.h"
+
+/* Return the first occurrence of NEEDLE in HAYSTACK.  Return HAYSTACK
+   if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
+   HAYSTACK.  */
+char *
+strstr (const char *haystack_start, const char *needle_start)
+{
+  const char *haystack = haystack_start;
+  const char *needle = needle_start;
+  size_t needle_len; /* Length of NEEDLE.  */
+  size_t haystack_len; /* Known minimum length of HAYSTACK.  */
+  bool ok = true; /* True if NEEDLE is prefix of HAYSTACK.  */
+
+  /* Determine length of NEEDLE, and in the process, make sure
+     HAYSTACK is at least as long (no point processing all of a long
+     NEEDLE if HAYSTACK is too short).  */
+  while (*haystack && *needle)
+    ok &= *haystack++ == *needle++;
+  if (*needle)
+    return NULL;
+  if (ok)
+    return (char *) haystack_start;
+
+  /* Reduce the size of haystack using strchr, since it has a smaller
+     linear coefficient than the Two-Way algorithm.  */
+  needle_len = needle - needle_start;
+  haystack = strchr (haystack_start + 1, *needle_start);
+  if (!haystack || __builtin_expect (needle_len == 1, 0))
+    return (char *) haystack;
+  needle -= needle_len;
+  haystack_len = (haystack > haystack_start + needle_len ? 1
+                  : needle_len + haystack_start - haystack);
+
+  /* Perform the search.  Abstract memory is considered to be an array
+     of 'unsigned char' values, not an array of 'char' values.  See
+     ISO C 99 section 6.2.6.1.  */
+  if (needle_len < LONG_NEEDLE_THRESHOLD)
+    return two_way_short_needle ((const unsigned char *) haystack,
+                                 haystack_len,
+                                 (const unsigned char *) needle, needle_len);
+  return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
+                              (const unsigned char *) needle, needle_len);
+}
+
+#undef LONG_NEEDLE_THRESHOLD