Source/WTF/wtf/text/AtomStringImpl.cpp - WebKit - Git at Google

 /*
  * Copyright (C) 2004-2008, 2013-2014 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Patrick Gansterer <paroga@paroga.com>
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2015 Yusuke Suzuki<utatane.tea@gmail.com>. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  *
  */

 #include "config.h"
 #include <wtf/text/AtomStringImpl.h>

 #include <wtf/Threading.h>
 #include <wtf/text/AtomStringTable.h>
 #include <wtf/text/StringHash.h>
 #include <wtf/unicode/UTF8Conversion.h>

 #if USE(WEB_THREAD)
 #include <wtf/Lock.h>
 #endif

 namespace WTF {

 using namespace Unicode;

 #if USE(WEB_THREAD)

 class AtomStringTableLocker : public LockHolder {
     WTF_MAKE_NONCOPYABLE(AtomStringTableLocker);

     static Lock s_stringTableLock;
 public:
     AtomStringTableLocker()
         : LockHolder(s_stringTableLock)
     {
     }
 };

 Lock AtomStringTableLocker::s_stringTableLock;

 #else

 class AtomStringTableLocker {
     WTF_MAKE_NONCOPYABLE(AtomStringTableLocker);
 public:
     AtomStringTableLocker() { }
 };

 #endif // USE(WEB_THREAD)

 using StringTableImpl = AtomStringTable::StringTableImpl;

 static ALWAYS_INLINE StringTableImpl& stringTable()
 {
     return Thread::current().atomStringTable()->table();
 }

 template<typename T, typename HashTranslator>
 static inline Ref<AtomStringImpl> addToStringTable(AtomStringTableLocker&, StringTableImpl& atomStringTable, const T& value)
 {
     auto addResult = atomStringTable.add<HashTranslator>(value);

     // If the string is newly-translated, then we need to adopt it.
     // The boolean in the pair tells us if that is so.
     if (addResult.isNewEntry)
         return adoptRef(static_cast<AtomStringImpl&>(*addResult.iterator->get()));
     return *static_cast<AtomStringImpl*>(addResult.iterator->get());
 }

 template<typename T, typename HashTranslator>
 static inline Ref<AtomStringImpl> addToStringTable(const T& value)
 {
     AtomStringTableLocker locker;
     return addToStringTable<T, HashTranslator>(locker, stringTable(), value);
 }

 struct CStringTranslator {
     static unsigned hash(const LChar* characters)
     {
         return StringHasher::computeHashAndMaskTop8Bits(characters);
     }

     static inline bool equal(PackedPtr<StringImpl> str, const LChar* characters)
     {
         return WTF::equal(str.get(), characters);
     }

     static void translate(PackedPtr<StringImpl>& location, const LChar* const& characters, unsigned hash)
     {
         auto* pointer = &StringImpl::create(characters).leakRef();
         pointer->setHash(hash);
         pointer->setIsAtom(true);
         location = pointer;
     }
 };

 RefPtr<AtomStringImpl> AtomStringImpl::add(const LChar* characters)
 {
     if (!characters)
         return nullptr;
     if (!*characters)
         return static_cast<AtomStringImpl*>(StringImpl::empty());

     return addToStringTable<const LChar*, CStringTranslator>(characters);
 }

 using UCharBuffer = HashTranslatorCharBuffer<UChar>;
 struct UCharBufferTranslator {
     static unsigned hash(const UCharBuffer& buf)
     {
         return buf.hash;
     }

     static bool equal(PackedPtr<StringImpl> const& str, const UCharBuffer& buf)
     {
         return WTF::equal(str.get(), buf.characters, buf.length);
     }

     static void translate(PackedPtr<StringImpl>& location, const UCharBuffer& buf, unsigned hash)
     {
         auto* pointer = &StringImpl::create8BitIfPossible(buf.characters, buf.length).leakRef();
         pointer->setHash(hash);
         pointer->setIsAtom(true);
         location = pointer;
     }
 };

 struct HashAndUTF8Characters {
     unsigned hash;
     const char* characters;
     unsigned length;
     unsigned utf16Length;
 };

 struct HashAndUTF8CharactersTranslator {
     static unsigned hash(const HashAndUTF8Characters& buffer)
     {
         return buffer.hash;
     }

     static bool equal(PackedPtr<StringImpl> const& passedString, const HashAndUTF8Characters& buffer)
     {
         auto* string = passedString.get();
         if (buffer.utf16Length != string->length())
             return false;

         // If buffer contains only ASCII characters UTF-8 and UTF16 length are the same.
         if (buffer.utf16Length != buffer.length) {
             if (string->is8Bit())
                 return equalLatin1WithUTF8(string->characters8(), buffer.characters, buffer.characters + buffer.length);

             return equalUTF16WithUTF8(string->characters16(), buffer.characters, buffer.characters + buffer.length);
         }

         if (string->is8Bit()) {
             const LChar* stringCharacters = string->characters8();

             for (unsigned i = 0; i < buffer.length; ++i) {
                 ASSERT(isASCII(buffer.characters[i]));
                 if (stringCharacters[i] != buffer.characters[i])
                     return false;
             }

             return true;
         }

         const UChar* stringCharacters = string->characters16();

         for (unsigned i = 0; i < buffer.length; ++i) {
             ASSERT(isASCII(buffer.characters[i]));
             if (stringCharacters[i] != buffer.characters[i])
                 return false;
         }

         return true;
     }

     static void translate(PackedPtr<StringImpl>& location, const HashAndUTF8Characters& buffer, unsigned hash)
     {
         UChar* target;
         auto newString = StringImpl::createUninitialized(buffer.utf16Length, target);

         bool isAllASCII;
         const char* source = buffer.characters;
         if (!convertUTF8ToUTF16(source, source + buffer.length, &target, target + buffer.utf16Length, &isAllASCII))
             ASSERT_NOT_REACHED();

         if (isAllASCII)
             newString = StringImpl::create(buffer.characters, buffer.length);

         auto* pointer = &newString.leakRef();
         pointer->setHash(hash);
         pointer->setIsAtom(true);
         location = pointer;
     }
 };

 RefPtr<AtomStringImpl> AtomStringImpl::add(const UChar* characters, unsigned length)
 {
     if (!characters)
         return nullptr;

     if (!length)
         return static_cast<AtomStringImpl*>(StringImpl::empty());

     UCharBuffer buffer { characters, length };
     return addToStringTable<UCharBuffer, UCharBufferTranslator>(buffer);
 }

 RefPtr<AtomStringImpl> AtomStringImpl::add(const UChar* characters)
 {
     if (!characters)
         return nullptr;

     unsigned length = 0;
     while (characters[length] != UChar(0))
         ++length;

     if (!length)
         return static_cast<AtomStringImpl*>(StringImpl::empty());

     UCharBuffer buffer { characters, length };
     return addToStringTable<UCharBuffer, UCharBufferTranslator>(buffer);
 }

 struct SubstringLocation {
     StringImpl* baseString;
     unsigned start;
     unsigned length;
 };

 struct SubstringTranslator {
     static void translate(PackedPtr<StringImpl>& location, const SubstringLocation& buffer, unsigned hash)
     {
         auto* pointer = &StringImpl::createSubstringSharingImpl(*buffer.baseString, buffer.start, buffer.length).leakRef();
         pointer->setHash(hash);
         pointer->setIsAtom(true);
         location = pointer;
     }
 };

 struct SubstringTranslator8 : SubstringTranslator {
     static unsigned hash(const SubstringLocation& buffer)
     {
         return StringHasher::computeHashAndMaskTop8Bits(buffer.baseString->characters8() + buffer.start, buffer.length);
     }

     static bool equal(PackedPtr<StringImpl> const& string, const SubstringLocation& buffer)
     {
         return WTF::equal(string.get(), buffer.baseString->characters8() + buffer.start, buffer.length);
     }
 };

 struct SubstringTranslator16 : SubstringTranslator {
     static unsigned hash(const SubstringLocation& buffer)
     {
         return StringHasher::computeHashAndMaskTop8Bits(buffer.baseString->characters16() + buffer.start, buffer.length);
     }

     static bool equal(PackedPtr<StringImpl> const& string, const SubstringLocation& buffer)
     {
         return WTF::equal(string.get(), buffer.baseString->characters16() + buffer.start, buffer.length);
     }
 };

 RefPtr<AtomStringImpl> AtomStringImpl::add(StringImpl* baseString, unsigned start, unsigned length)
 {
     if (!baseString)
         return nullptr;

     if (!length || start >= baseString->length())
         return static_cast<AtomStringImpl*>(StringImpl::empty());

     unsigned maxLength = baseString->length() - start;
     if (length >= maxLength) {
         if (!start)
             return add(baseString);
         length = maxLength;
     }

     SubstringLocation buffer = { baseString, start, length };
     if (baseString->is8Bit())
         return addToStringTable<SubstringLocation, SubstringTranslator8>(buffer);
     return addToStringTable<SubstringLocation, SubstringTranslator16>(buffer);
 }

 using LCharBuffer = HashTranslatorCharBuffer<LChar>;
 struct LCharBufferTranslator {
     static unsigned hash(const LCharBuffer& buf)
     {
         return buf.hash;
     }

     static bool equal(PackedPtr<StringImpl> const& str, const LCharBuffer& buf)
     {
         return WTF::equal(str.get(), buf.characters, buf.length);
     }

     static void translate(PackedPtr<StringImpl>& location, const LCharBuffer& buf, unsigned hash)
     {
         auto* pointer = &StringImpl::create(buf.characters, buf.length).leakRef();
         pointer->setHash(hash);
         pointer->setIsAtom(true);
         location = pointer;
     }
 };

 template<typename CharType>
 struct BufferFromStaticDataTranslator {
     using Buffer = HashTranslatorCharBuffer<CharType>;
     static unsigned hash(const Buffer& buf)
     {
         return buf.hash;
     }

     static bool equal(PackedPtr<StringImpl> const& str, const Buffer& buf)
     {
         return WTF::equal(str.get(), buf.characters, buf.length);
     }

     static void translate(PackedPtr<StringImpl>& location, const Buffer& buf, unsigned hash)
     {
         auto* pointer = &StringImpl::createWithoutCopying(buf.characters, buf.length).leakRef();
         pointer->setHash(hash);
         pointer->setIsAtom(true);
         location = pointer;
     }
 };

 RefPtr<AtomStringImpl> AtomStringImpl::add(const LChar* characters, unsigned length)
 {
     if (!characters)
         return nullptr;

     if (!length)
         return static_cast<AtomStringImpl*>(StringImpl::empty());

     LCharBuffer buffer { characters, length };
     return addToStringTable<LCharBuffer, LCharBufferTranslator>(buffer);
 }

 Ref<AtomStringImpl> AtomStringImpl::addLiteral(const char* characters, unsigned length)
 {
     ASSERT(characters);
     ASSERT(length);

     LCharBuffer buffer { reinterpret_cast<const LChar*>(characters), length };
     return addToStringTable<LCharBuffer, BufferFromStaticDataTranslator<LChar>>(buffer);
 }

 static Ref<AtomStringImpl> addSymbol(AtomStringTableLocker& locker, StringTableImpl& atomStringTable, StringImpl& base)
 {
     ASSERT(base.length());
     ASSERT(base.isSymbol());

     SubstringLocation buffer = { &base, 0, base.length() };
     if (base.is8Bit())
         return addToStringTable<SubstringLocation, SubstringTranslator8>(locker, atomStringTable, buffer);
     return addToStringTable<SubstringLocation, SubstringTranslator16>(locker, atomStringTable, buffer);
 }

 static inline Ref<AtomStringImpl> addSymbol(StringImpl& base)
 {
     AtomStringTableLocker locker;
     return addSymbol(locker, stringTable(), base);
 }

 static Ref<AtomStringImpl> addStatic(AtomStringTableLocker& locker, StringTableImpl& atomStringTable, const StringImpl& base)
 {
     ASSERT(base.length());
     ASSERT(base.isStatic());

     if (base.is8Bit()) {
         LCharBuffer buffer { base.characters8(), base.length(), base.hash() };
         return addToStringTable<LCharBuffer, BufferFromStaticDataTranslator<LChar>>(locker, atomStringTable, buffer);
     }
     UCharBuffer buffer { base.characters16(), base.length(), base.hash() };
     return addToStringTable<UCharBuffer, BufferFromStaticDataTranslator<UChar>>(locker, atomStringTable, buffer);
 }

 static inline Ref<AtomStringImpl> addStatic(const StringImpl& base)
 {
     AtomStringTableLocker locker;
     return addStatic(locker, stringTable(), base);
 }

 RefPtr<AtomStringImpl> AtomStringImpl::add(const StaticStringImpl* string)
 {
     auto s = reinterpret_cast<const StringImpl*>(string);
     ASSERT(s->isStatic());
     return addStatic(*s);
 }

 Ref<AtomStringImpl> AtomStringImpl::addSlowCase(StringImpl& string)
 {
     // This check is necessary for null symbols.
     // Their length is zero, but they are not AtomStringImpl.
     if (!string.length())
         return *static_cast<AtomStringImpl*>(StringImpl::empty());

     if (string.isStatic())
         return addStatic(string);

     if (string.isSymbol())
         return addSymbol(string);

     ASSERT_WITH_MESSAGE(!string.isAtom(), "AtomStringImpl should not hit the slow case if the string is already an atom.");

     AtomStringTableLocker locker;
     auto addResult = stringTable().add(&string);

     if (addResult.isNewEntry) {
         ASSERT(addResult.iterator->get() == &string);
         string.setIsAtom(true);
     }

     return *static_cast<AtomStringImpl*>(addResult.iterator->get());
 }

 Ref<AtomStringImpl> AtomStringImpl::addSlowCase(AtomStringTable& stringTable, StringImpl& string)
 {
     // This check is necessary for null symbols.
     // Their length is zero, but they are not AtomStringImpl.
     if (!string.length())
         return *static_cast<AtomStringImpl*>(StringImpl::empty());

     if (string.isStatic()) {
         AtomStringTableLocker locker;
         return addStatic(locker, stringTable.table(), string);
     }

     if (string.isSymbol()) {
         AtomStringTableLocker locker;
         return addSymbol(locker, stringTable.table(), string);
     }

     ASSERT_WITH_MESSAGE(!string.isAtom(), "AtomStringImpl should not hit the slow case if the string is already an atom.");

     AtomStringTableLocker locker;
     auto addResult = stringTable.table().add(&string);

     if (addResult.isNewEntry) {
         ASSERT(addResult.iterator->get() == &string);
         string.setIsAtom(true);
     }

     return *static_cast<AtomStringImpl*>(addResult.iterator->get());
 }

 void AtomStringImpl::remove(AtomStringImpl* string)
 {
     ASSERT(string->isAtom());
     AtomStringTableLocker locker;
     auto& atomStringTable = stringTable();
     auto iterator = atomStringTable.find(string);
     ASSERT_WITH_MESSAGE(iterator != atomStringTable.end(), "The string being removed is an atom in the string table of an other thread!");
     ASSERT(string == iterator->get());
     atomStringTable.remove(iterator);
 }

 RefPtr<AtomStringImpl> AtomStringImpl::lookUpSlowCase(StringImpl& string)
 {
     ASSERT_WITH_MESSAGE(!string.isAtom(), "AtomStringImpl objects should return from the fast case.");

     if (!string.length())
         return static_cast<AtomStringImpl*>(StringImpl::empty());

     AtomStringTableLocker locker;
     auto& atomStringTable = stringTable();
     auto iterator = atomStringTable.find(&string);
     if (iterator != atomStringTable.end())
         return static_cast<AtomStringImpl*>(iterator->get());
     return nullptr;
 }

 RefPtr<AtomStringImpl> AtomStringImpl::addUTF8(const char* charactersStart, const char* charactersEnd)
 {
     HashAndUTF8Characters buffer;
     buffer.characters = charactersStart;
     buffer.hash = calculateStringHashAndLengthFromUTF8MaskingTop8Bits(charactersStart, charactersEnd, buffer.length, buffer.utf16Length);

     if (!buffer.hash)
         return nullptr;

     return addToStringTable<HashAndUTF8Characters, HashAndUTF8CharactersTranslator>(buffer);
 }

 RefPtr<AtomStringImpl> AtomStringImpl::lookUp(const LChar* characters, unsigned length)
 {
     AtomStringTableLocker locker;
     auto& table = stringTable();

     LCharBuffer buffer = { characters, length };
     auto iterator = table.find<LCharBufferTranslator>(buffer);
     if (iterator != table.end())
         return static_cast<AtomStringImpl*>(iterator->get());
     return nullptr;
 }

 RefPtr<AtomStringImpl> AtomStringImpl::lookUp(const UChar* characters, unsigned length)
 {
     AtomStringTableLocker locker;
     auto& table = stringTable();

     UCharBuffer buffer { characters, length };
     auto iterator = table.find<UCharBufferTranslator>(buffer);
     if (iterator != table.end())
         return static_cast<AtomStringImpl*>(iterator->get());
     return nullptr;
 }

 #if ASSERT_ENABLED
 bool AtomStringImpl::isInAtomStringTable(StringImpl* string)
 {
     AtomStringTableLocker locker;
     return stringTable().contains(string);
 }
 #endif

 } // namespace WTF
	/*
	* Copyright (C) 2004-2008, 2013-2014 Apple Inc. All rights reserved.
	* Copyright (C) 2010 Patrick Gansterer <paroga@paroga.com>
	* Copyright (C) 2012 Google Inc. All rights reserved.
	* Copyright (C) 2015 Yusuke Suzuki<utatane.tea@gmail.com>. All rights reserved.
	*
	* This library is free software; you can redistribute it and/or
	* modify it under the terms of the GNU Library General Public
	* License as published by the Free Software Foundation; either
	* version 2 of the License, or (at your option) any later version.
	*
	* This library is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	* Library General Public License for more details.
	*
	* You should have received a copy of the GNU Library General Public License
	* along with this library; see the file COPYING.LIB. If not, write to
	* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
	* Boston, MA 02110-1301, USA.
	*
	*/

	#include "config.h"
	#include <wtf/text/AtomStringImpl.h>

	#include <wtf/Threading.h>
	#include <wtf/text/AtomStringTable.h>
	#include <wtf/text/StringHash.h>
	#include <wtf/unicode/UTF8Conversion.h>

	#if USE(WEB_THREAD)
	#include <wtf/Lock.h>
	#endif

	namespace WTF {

	using namespace Unicode;

	#if USE(WEB_THREAD)

	class AtomStringTableLocker : public LockHolder {
	WTF_MAKE_NONCOPYABLE(AtomStringTableLocker);

	static Lock s_stringTableLock;
	public:
	AtomStringTableLocker()
	: LockHolder(s_stringTableLock)
	{
	}
	};

	Lock AtomStringTableLocker::s_stringTableLock;

	#else

	class AtomStringTableLocker {
	WTF_MAKE_NONCOPYABLE(AtomStringTableLocker);
	public:
	AtomStringTableLocker() { }
	};

	#endif // USE(WEB_THREAD)

	using StringTableImpl = AtomStringTable::StringTableImpl;

	static ALWAYS_INLINE StringTableImpl& stringTable()
	{
	return Thread::current().atomStringTable()->table();
	}

	template<typename T, typename HashTranslator>
	static inline Ref<AtomStringImpl> addToStringTable(AtomStringTableLocker&, StringTableImpl& atomStringTable, const T& value)
	{
	auto addResult = atomStringTable.add<HashTranslator>(value);

	// If the string is newly-translated, then we need to adopt it.
	// The boolean in the pair tells us if that is so.
	if (addResult.isNewEntry)
	return adoptRef(static_cast<AtomStringImpl&>(*addResult.iterator->get()));
	return static_cast<AtomStringImpl>(addResult.iterator->get());
	}

	template<typename T, typename HashTranslator>
	static inline Ref<AtomStringImpl> addToStringTable(const T& value)
	{
	AtomStringTableLocker locker;
	return addToStringTable<T, HashTranslator>(locker, stringTable(), value);
	}

	struct CStringTranslator {
	static unsigned hash(const LChar* characters)
	{
	return StringHasher::computeHashAndMaskTop8Bits(characters);
	}

	static inline bool equal(PackedPtr<StringImpl> str, const LChar* characters)
	{
	return WTF::equal(str.get(), characters);
	}

	static void translate(PackedPtr<StringImpl>& location, const LChar* const& characters, unsigned hash)
	{
	auto* pointer = &StringImpl::create(characters).leakRef();
	pointer->setHash(hash);
	pointer->setIsAtom(true);
	location = pointer;
	}
	};

	RefPtr<AtomStringImpl> AtomStringImpl::add(const LChar* characters)
	{
	if (!characters)
	return nullptr;
	if (!*characters)
	return static_cast<AtomStringImpl*>(StringImpl::empty());

	return addToStringTable<const LChar*, CStringTranslator>(characters);
	}

	using UCharBuffer = HashTranslatorCharBuffer<UChar>;
	struct UCharBufferTranslator {
	static unsigned hash(const UCharBuffer& buf)
	{
	return buf.hash;
	}

	static bool equal(PackedPtr<StringImpl> const& str, const UCharBuffer& buf)
	{
	return WTF::equal(str.get(), buf.characters, buf.length);
	}

	static void translate(PackedPtr<StringImpl>& location, const UCharBuffer& buf, unsigned hash)
	{
	auto* pointer = &StringImpl::create8BitIfPossible(buf.characters, buf.length).leakRef();
	pointer->setHash(hash);
	pointer->setIsAtom(true);
	location = pointer;
	}
	};

	struct HashAndUTF8Characters {
	unsigned hash;
	const char* characters;
	unsigned length;
	unsigned utf16Length;
	};

	struct HashAndUTF8CharactersTranslator {
	static unsigned hash(const HashAndUTF8Characters& buffer)
	{
	return buffer.hash;
	}

	static bool equal(PackedPtr<StringImpl> const& passedString, const HashAndUTF8Characters& buffer)
	{
	auto* string = passedString.get();
	if (buffer.utf16Length != string->length())
	return false;

	// If buffer contains only ASCII characters UTF-8 and UTF16 length are the same.
	if (buffer.utf16Length != buffer.length) {
	if (string->is8Bit())
	return equalLatin1WithUTF8(string->characters8(), buffer.characters, buffer.characters + buffer.length);

	return equalUTF16WithUTF8(string->characters16(), buffer.characters, buffer.characters + buffer.length);
	}

	if (string->is8Bit()) {
	const LChar* stringCharacters = string->characters8();

	for (unsigned i = 0; i < buffer.length; ++i) {
	ASSERT(isASCII(buffer.characters[i]));
	if (stringCharacters[i] != buffer.characters[i])
	return false;
	}

	return true;
	}

	const UChar* stringCharacters = string->characters16();

	for (unsigned i = 0; i < buffer.length; ++i) {
	ASSERT(isASCII(buffer.characters[i]));
	if (stringCharacters[i] != buffer.characters[i])
	return false;
	}

	return true;
	}

	static void translate(PackedPtr<StringImpl>& location, const HashAndUTF8Characters& buffer, unsigned hash)
	{
	UChar* target;
	auto newString = StringImpl::createUninitialized(buffer.utf16Length, target);

	bool isAllASCII;
	const char* source = buffer.characters;
	if (!convertUTF8ToUTF16(source, source + buffer.length, &target, target + buffer.utf16Length, &isAllASCII))
	ASSERT_NOT_REACHED();

	if (isAllASCII)
	newString = StringImpl::create(buffer.characters, buffer.length);

	auto* pointer = &newString.leakRef();
	pointer->setHash(hash);
	pointer->setIsAtom(true);
	location = pointer;
	}
	};

	RefPtr<AtomStringImpl> AtomStringImpl::add(const UChar* characters, unsigned length)
	{
	if (!characters)
	return nullptr;

	if (!length)
	return static_cast<AtomStringImpl*>(StringImpl::empty());

	UCharBuffer buffer { characters, length };
	return addToStringTable<UCharBuffer, UCharBufferTranslator>(buffer);
	}

	RefPtr<AtomStringImpl> AtomStringImpl::add(const UChar* characters)
	{
	if (!characters)
	return nullptr;

	unsigned length = 0;
	while (characters[length] != UChar(0))
	++length;

	if (!length)
	return static_cast<AtomStringImpl*>(StringImpl::empty());

	UCharBuffer buffer { characters, length };
	return addToStringTable<UCharBuffer, UCharBufferTranslator>(buffer);
	}

	struct SubstringLocation {
	StringImpl* baseString;
	unsigned start;
	unsigned length;
	};

	struct SubstringTranslator {
	static void translate(PackedPtr<StringImpl>& location, const SubstringLocation& buffer, unsigned hash)
	{
	auto* pointer = &StringImpl::createSubstringSharingImpl(*buffer.baseString, buffer.start, buffer.length).leakRef();
	pointer->setHash(hash);
	pointer->setIsAtom(true);
	location = pointer;
	}
	};

	struct SubstringTranslator8 : SubstringTranslator {
	static unsigned hash(const SubstringLocation& buffer)
	{
	return StringHasher::computeHashAndMaskTop8Bits(buffer.baseString->characters8() + buffer.start, buffer.length);
	}

	static bool equal(PackedPtr<StringImpl> const& string, const SubstringLocation& buffer)
	{
	return WTF::equal(string.get(), buffer.baseString->characters8() + buffer.start, buffer.length);
	}
	};

	struct SubstringTranslator16 : SubstringTranslator {
	static unsigned hash(const SubstringLocation& buffer)
	{
	return StringHasher::computeHashAndMaskTop8Bits(buffer.baseString->characters16() + buffer.start, buffer.length);
	}

	static bool equal(PackedPtr<StringImpl> const& string, const SubstringLocation& buffer)
	{
	return WTF::equal(string.get(), buffer.baseString->characters16() + buffer.start, buffer.length);
	}
	};

	RefPtr<AtomStringImpl> AtomStringImpl::add(StringImpl* baseString, unsigned start, unsigned length)
	{
	if (!baseString)
	return nullptr;

	if (!length \|\| start >= baseString->length())
	return static_cast<AtomStringImpl*>(StringImpl::empty());

	unsigned maxLength = baseString->length() - start;
	if (length >= maxLength) {
	if (!start)
	return add(baseString);
	length = maxLength;
	}

	SubstringLocation buffer = { baseString, start, length };
	if (baseString->is8Bit())
	return addToStringTable<SubstringLocation, SubstringTranslator8>(buffer);
	return addToStringTable<SubstringLocation, SubstringTranslator16>(buffer);
	}

	using LCharBuffer = HashTranslatorCharBuffer<LChar>;
	struct LCharBufferTranslator {
	static unsigned hash(const LCharBuffer& buf)
	{
	return buf.hash;
	}

	static bool equal(PackedPtr<StringImpl> const& str, const LCharBuffer& buf)
	{
	return WTF::equal(str.get(), buf.characters, buf.length);
	}

	static void translate(PackedPtr<StringImpl>& location, const LCharBuffer& buf, unsigned hash)
	{
	auto* pointer = &StringImpl::create(buf.characters, buf.length).leakRef();
	pointer->setHash(hash);
	pointer->setIsAtom(true);
	location = pointer;
	}
	};

	template<typename CharType>
	struct BufferFromStaticDataTranslator {
	using Buffer = HashTranslatorCharBuffer<CharType>;
	static unsigned hash(const Buffer& buf)
	{
	return buf.hash;
	}

	static bool equal(PackedPtr<StringImpl> const& str, const Buffer& buf)
	{
	return WTF::equal(str.get(), buf.characters, buf.length);
	}

	static void translate(PackedPtr<StringImpl>& location, const Buffer& buf, unsigned hash)
	{
	auto* pointer = &StringImpl::createWithoutCopying(buf.characters, buf.length).leakRef();
	pointer->setHash(hash);
	pointer->setIsAtom(true);
	location = pointer;
	}
	};

	RefPtr<AtomStringImpl> AtomStringImpl::add(const LChar* characters, unsigned length)
	{
	if (!characters)
	return nullptr;

	if (!length)
	return static_cast<AtomStringImpl*>(StringImpl::empty());

	LCharBuffer buffer { characters, length };
	return addToStringTable<LCharBuffer, LCharBufferTranslator>(buffer);
	}

	Ref<AtomStringImpl> AtomStringImpl::addLiteral(const char* characters, unsigned length)
	{
	ASSERT(characters);
	ASSERT(length);

	LCharBuffer buffer { reinterpret_cast<const LChar*>(characters), length };
	return addToStringTable<LCharBuffer, BufferFromStaticDataTranslator<LChar>>(buffer);
	}

	static Ref<AtomStringImpl> addSymbol(AtomStringTableLocker& locker, StringTableImpl& atomStringTable, StringImpl& base)
	{
	ASSERT(base.length());
	ASSERT(base.isSymbol());

	SubstringLocation buffer = { &base, 0, base.length() };
	if (base.is8Bit())
	return addToStringTable<SubstringLocation, SubstringTranslator8>(locker, atomStringTable, buffer);
	return addToStringTable<SubstringLocation, SubstringTranslator16>(locker, atomStringTable, buffer);
	}

	static inline Ref<AtomStringImpl> addSymbol(StringImpl& base)
	{
	AtomStringTableLocker locker;
	return addSymbol(locker, stringTable(), base);
	}

	static Ref<AtomStringImpl> addStatic(AtomStringTableLocker& locker, StringTableImpl& atomStringTable, const StringImpl& base)
	{
	ASSERT(base.length());
	ASSERT(base.isStatic());

	if (base.is8Bit()) {
	LCharBuffer buffer { base.characters8(), base.length(), base.hash() };
	return addToStringTable<LCharBuffer, BufferFromStaticDataTranslator<LChar>>(locker, atomStringTable, buffer);
	}
	UCharBuffer buffer { base.characters16(), base.length(), base.hash() };
	return addToStringTable<UCharBuffer, BufferFromStaticDataTranslator<UChar>>(locker, atomStringTable, buffer);
	}

	static inline Ref<AtomStringImpl> addStatic(const StringImpl& base)
	{
	AtomStringTableLocker locker;
	return addStatic(locker, stringTable(), base);
	}

	RefPtr<AtomStringImpl> AtomStringImpl::add(const StaticStringImpl* string)
	{
	auto s = reinterpret_cast<const StringImpl*>(string);
	ASSERT(s->isStatic());
	return addStatic(*s);
	}

	Ref<AtomStringImpl> AtomStringImpl::addSlowCase(StringImpl& string)
	{
	// This check is necessary for null symbols.
	// Their length is zero, but they are not AtomStringImpl.
	if (!string.length())
	return static_cast<AtomStringImpl>(StringImpl::empty());

	if (string.isStatic())
	return addStatic(string);

	if (string.isSymbol())
	return addSymbol(string);

	ASSERT_WITH_MESSAGE(!string.isAtom(), "AtomStringImpl should not hit the slow case if the string is already an atom.");

	AtomStringTableLocker locker;
	auto addResult = stringTable().add(&string);

	if (addResult.isNewEntry) {
	ASSERT(addResult.iterator->get() == &string);
	string.setIsAtom(true);
	}

	return static_cast<AtomStringImpl>(addResult.iterator->get());
	}

	Ref<AtomStringImpl> AtomStringImpl::addSlowCase(AtomStringTable& stringTable, StringImpl& string)
	{
	// This check is necessary for null symbols.
	// Their length is zero, but they are not AtomStringImpl.
	if (!string.length())
	return static_cast<AtomStringImpl>(StringImpl::empty());

	if (string.isStatic()) {
	AtomStringTableLocker locker;
	return addStatic(locker, stringTable.table(), string);
	}

	if (string.isSymbol()) {
	AtomStringTableLocker locker;
	return addSymbol(locker, stringTable.table(), string);
	}

	ASSERT_WITH_MESSAGE(!string.isAtom(), "AtomStringImpl should not hit the slow case if the string is already an atom.");

	AtomStringTableLocker locker;
	auto addResult = stringTable.table().add(&string);

	if (addResult.isNewEntry) {
	ASSERT(addResult.iterator->get() == &string);
	string.setIsAtom(true);
	}

	return static_cast<AtomStringImpl>(addResult.iterator->get());
	}

	void AtomStringImpl::remove(AtomStringImpl* string)
	{
	ASSERT(string->isAtom());
	AtomStringTableLocker locker;
	auto& atomStringTable = stringTable();
	auto iterator = atomStringTable.find(string);
	ASSERT_WITH_MESSAGE(iterator != atomStringTable.end(), "The string being removed is an atom in the string table of an other thread!");
	ASSERT(string == iterator->get());
	atomStringTable.remove(iterator);
	}

	RefPtr<AtomStringImpl> AtomStringImpl::lookUpSlowCase(StringImpl& string)
	{
	ASSERT_WITH_MESSAGE(!string.isAtom(), "AtomStringImpl objects should return from the fast case.");

	if (!string.length())
	return static_cast<AtomStringImpl*>(StringImpl::empty());

	AtomStringTableLocker locker;
	auto& atomStringTable = stringTable();
	auto iterator = atomStringTable.find(&string);
	if (iterator != atomStringTable.end())
	return static_cast<AtomStringImpl*>(iterator->get());
	return nullptr;
	}

	RefPtr<AtomStringImpl> AtomStringImpl::addUTF8(const char* charactersStart, const char* charactersEnd)
	{
	HashAndUTF8Characters buffer;
	buffer.characters = charactersStart;
	buffer.hash = calculateStringHashAndLengthFromUTF8MaskingTop8Bits(charactersStart, charactersEnd, buffer.length, buffer.utf16Length);

	if (!buffer.hash)
	return nullptr;

	return addToStringTable<HashAndUTF8Characters, HashAndUTF8CharactersTranslator>(buffer);
	}

	RefPtr<AtomStringImpl> AtomStringImpl::lookUp(const LChar* characters, unsigned length)
	{
	AtomStringTableLocker locker;
	auto& table = stringTable();

	LCharBuffer buffer = { characters, length };
	auto iterator = table.find<LCharBufferTranslator>(buffer);
	if (iterator != table.end())
	return static_cast<AtomStringImpl*>(iterator->get());
	return nullptr;
	}

	RefPtr<AtomStringImpl> AtomStringImpl::lookUp(const UChar* characters, unsigned length)
	{
	AtomStringTableLocker locker;
	auto& table = stringTable();

	UCharBuffer buffer { characters, length };
	auto iterator = table.find<UCharBufferTranslator>(buffer);
	if (iterator != table.end())
	return static_cast<AtomStringImpl*>(iterator->get());
	return nullptr;
	}

	#if ASSERT_ENABLED
	bool AtomStringImpl::isInAtomStringTable(StringImpl* string)
	{
	AtomStringTableLocker locker;
	return stringTable().contains(string);
	}
	#endif

	} // namespace WTF