1/* Copyright (C) 1991,92,93,94,96,97,98,2000,2004,2007,2011 Free Software Foundation, Inc.
2   This file is part of the GNU C Library.
3
4   This program is free software; you can redistribute it and/or modify
5   it under the terms of the GNU General Public License as published by
6   the Free Software Foundation; either version 2, or (at your option)
7   any later version.
8
9   This program is distributed in the hope that it will be useful,
10   but WITHOUT ANY WARRANTY; without even the implied warranty of
11   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12   GNU General Public License for more details.
13
14   You should have received a copy of the GNU General Public License along
15   with this program; if not, write to the Free Software Foundation,
16   Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
17
18/*
19
20@deftypefn Supplemental void* memmem (const void *@var{haystack}, @
21  size_t @var{haystack_len} const void *@var{needle}, size_t @var{needle_len})
22
23Returns a pointer to the first occurrence of @var{needle} (length
24@var{needle_len}) in @var{haystack} (length @var{haystack_len}).
25Returns @code{NULL} if not found.
26
27@end deftypefn
28
29*/
30
31#ifndef _LIBC
32# include <config.h>
33#endif
34
35#include <stddef.h>
36#include <string.h>
37
38#ifndef _LIBC
39# define __builtin_expect(expr, val)   (expr)
40#endif
41
42#undef memmem
43
44/* Return the first occurrence of NEEDLE in HAYSTACK.  */
45void *
46memmem (const void *haystack, size_t haystack_len, const void *needle,
47	size_t needle_len)
48{
49  const char *begin;
50  const char *const last_possible
51    = (const char *) haystack + haystack_len - needle_len;
52
53  if (needle_len == 0)
54    /* The first occurrence of the empty string is deemed to occur at
55       the beginning of the string.  */
56    return (void *) haystack;
57
58  /* Sanity check, otherwise the loop might search through the whole
59     memory.  */
60  if (__builtin_expect (haystack_len < needle_len, 0))
61    return NULL;
62
63  for (begin = (const char *) haystack; begin <= last_possible; ++begin)
64    if (begin[0] == ((const char *) needle)[0] &&
65	!memcmp ((const void *) &begin[1],
66		 (const void *) ((const char *) needle + 1),
67		 needle_len - 1))
68      return (void *) begin;
69
70  return NULL;
71}
72