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
memmem(const void * void_haystack,size_t n,const void * void_needle,size_t m)31 void* 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 const_cast<void*>(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