60 lines
2.3 KiB
C++
60 lines
2.3 KiB
C++
/*
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* Copyright (C) 2008 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <string.h>
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void* memmem(const void* void_haystack, size_t n, const void* void_needle, size_t m) {
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const unsigned char* haystack = reinterpret_cast<const unsigned char*>(void_haystack);
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const unsigned char* needle = reinterpret_cast<const unsigned char*>(void_needle);
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if (n < m) return nullptr;
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if (m == 0) return const_cast<void*>(void_haystack);
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if (m == 1) return memchr(haystack, needle[0], n);
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// This uses the "Not So Naive" algorithm, a very simple but usually effective algorithm.
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// http://www-igm.univ-mlv.fr/~lecroq/string/
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const unsigned char* y = haystack;
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const unsigned char* x = needle;
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size_t j = 0;
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size_t k = 1, l = 2;
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if (x[0] == x[1]) {
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k = 2;
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l = 1;
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}
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while (j <= n-m) {
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if (x[1] != y[j+1]) {
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j += k;
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} else {
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if (!memcmp(x+2, y+j+2, m-2) && x[0] == y[j]) return const_cast<unsigned char*>(&y[j]);
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j += l;
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}
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}
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return nullptr;
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}
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