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 
23 Returns a pointer to the first occurrence of @var{needle} (length
24 @var{needle_len}) in @var{haystack} (length @var{haystack_len}).
25 Returns @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.  */
45 void *
memmem(const void * haystack,size_t haystack_len,const void * needle,size_t needle_len)46 memmem (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