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/*
* Copyright (C) 2022 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
* THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <limits>
#include <wtf/text/StringCommon.h>
#include <wtf/text/StringView.h>
namespace WTF {
template<typename OffsetType>
class BoyerMooreHorspoolTable {
WTF_MAKE_FAST_ALLOCATED(BoyerMooreHorspoolTable);
public:
static constexpr unsigned size = 256;
static constexpr unsigned maxPatternLength = std::numeric_limits<OffsetType>::max();
explicit BoyerMooreHorspoolTable(StringView pattern)
{
if (pattern.is8Bit())
initializeTable(pattern.span8());
else
initializeTable(pattern.span16());
}
explicit constexpr BoyerMooreHorspoolTable(ASCIILiteral pattern)
{
initializeTable(pattern.span8());
}
ALWAYS_INLINE size_t find(StringView string, StringView matchString) const
{
unsigned matchLength = matchString.length();
if (matchLength > string.length())
return notFound;
if (UNLIKELY(!matchLength))
return 0;
if (string.is8Bit()) {
if (matchString.is8Bit())
return findInner(string.span8(), matchString.span8());
return findInner(string.span8(), matchString.span16());
}
if (matchString.is8Bit())
return findInner(string.span16(), matchString.span8());
return findInner(string.span16(), matchString.span16());
}
private:
template<typename CharacterType>
constexpr void initializeTable(std::span<CharacterType> pattern)
{
size_t length = pattern.size();
ASSERT_UNDER_CONSTEXPR_CONTEXT(length <= maxPatternLength);
if (length) {
for (auto& element : m_table)
element = length;
for (unsigned i = 0; i < (pattern.size() - 1); ++i) {
unsigned index = pattern[i] & 0xff;
m_table[index] = length - 1 - i;
}
}
}
template <typename SearchCharacterType, typename MatchCharacterType>
ALWAYS_INLINE size_t findInner(std::span<const SearchCharacterType> characters, std::span<const MatchCharacterType> matchCharacters) const
{
size_t cursor = 0;
size_t last = characters.size() - matchCharacters.size();
while (cursor <= last) {
if (equal(characters.subspan(cursor).data(), matchCharacters))
return cursor;
cursor += m_table[static_cast<uint8_t>(characters[cursor + matchCharacters.size() - 1])];
}
return notFound;
}
std::array<OffsetType, size> m_table;
};
}
using WTF::BoyerMooreHorspoolTable;
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