mirror of
https://github.com/SerenityOS/serenity
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88 lines
3 KiB
C++
88 lines
3 KiB
C++
/*
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* Copyright (c) 2020, the SerenityOS developers.
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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 are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED 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 OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <AK/Assertions.h>
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#include <AK/Types.h>
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namespace AK {
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namespace {
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const static void* bitap_bitwise(const void* haystack, size_t haystack_length, const void* needle, size_t needle_length)
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{
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ASSERT(needle_length < 32);
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u64 lookup = 0xfffffffe;
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constexpr size_t mask_length = (size_t)((u8)-1) + 1;
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u64 needle_mask[mask_length];
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for (size_t i = 0; i < mask_length; ++i)
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needle_mask[i] = 0xffffffff;
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for (size_t i = 0; i < needle_length; ++i)
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needle_mask[((const u8*)needle)[i]] &= ~(0x00000001 << i);
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for (size_t i = 0; i < haystack_length; ++i) {
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lookup |= needle_mask[((const u8*)haystack)[i]];
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lookup <<= 1;
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if (!(lookup & (0x00000001 << needle_length)))
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return ((const u8*)haystack) + i - needle_length + 1;
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}
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return nullptr;
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}
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}
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static inline const void* memmem(const void* haystack, size_t haystack_length, const void* needle, size_t needle_length)
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{
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if (needle_length == 0)
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return haystack;
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if (haystack_length < needle_length)
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return nullptr;
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if (haystack_length == needle_length)
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return __builtin_memcmp(haystack, needle, haystack_length) == 0 ? haystack : nullptr;
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if (needle_length < 32)
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return bitap_bitwise(haystack, haystack_length, needle, needle_length);
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// Fallback to a slower search.
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auto length_diff = haystack_length - needle_length;
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for (size_t i = 0; i < length_diff; ++i) {
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const auto* start = ((const u8*)haystack) + i;
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if (__builtin_memcmp(start, needle, needle_length) == 0)
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return start;
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}
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return nullptr;
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}
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}
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