1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#include <string.h>
30
31void* memmem(const void* void_haystack, size_t n, const void* void_needle, size_t m) {
32  const unsigned char* haystack = reinterpret_cast<const unsigned char*>(void_haystack);
33  const unsigned char* needle = reinterpret_cast<const unsigned char*>(void_needle);
34
35  if (n < m) return nullptr;
36
37  if (m == 0) return const_cast<void*>(void_haystack);
38  if (m == 1) return memchr(haystack, needle[0], n);
39
40  // This uses the "Not So Naive" algorithm, a very simple but usually effective algorithm.
41  // http://www-igm.univ-mlv.fr/~lecroq/string/
42  const unsigned char* y = haystack;
43  const unsigned char* x = needle;
44  size_t j = 0;
45  size_t k = 1, l = 2;
46
47  if (x[0] == x[1]) {
48    k = 2;
49    l = 1;
50  }
51  while (j <= n-m) {
52    if (x[1] != y[j+1]) {
53      j += k;
54    } else {
55      if (!memcmp(x+2, y+j+2, m-2) && x[0] == y[j]) return const_cast<unsigned char*>(&y[j]);
56      j += l;
57    }
58  }
59  return nullptr;
60}
61