third_party/WebKit/Source/wtf/StringHasher.h - chromium/src - Git at Google

 /*
  * Copyright (C) 2005, 2006, 2008, 2010, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Patrick Gansterer <paroga@paroga.com>
  *
  * 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.
  *
  */

 #ifndef WTF_StringHasher_h
 #define WTF_StringHasher_h

 #include "wtf/text/Unicode.h"

 namespace WTF {

 // Paul Hsieh's SuperFastHash
 // http://www.azillionmonkeys.com/qed/hash.html

 // LChar data is interpreted as Latin-1-encoded (zero extended to 16 bits).

 // NOTE: The hash computation here must stay in sync with the create_hash_table script in
 // JavaScriptCore and the CodeGeneratorJS.pm script in WebCore.

 // Golden ratio. Arbitrary start value to avoid mapping all zeros to a hash value of zero.
 static const unsigned stringHashingStartValue = 0x9E3779B9U;

 class StringHasher {
 public:
     static const unsigned flagCount = 8; // Save 8 bits for StringImpl to use as flags.

     StringHasher()
         : m_hash(stringHashingStartValue)
         , m_hasPendingCharacter(false)
         , m_pendingCharacter(0)
     {
     }

     // The hasher hashes two characters at a time, and thus an "aligned" hasher is one
     // where an even number of characters have been added. Callers that always add
     // characters two at a time can use the "assuming aligned" functions.
     void addCharactersAssumingAligned(UChar a, UChar b)
     {
         ASSERT(!m_hasPendingCharacter);
         m_hash += a;
         m_hash = (m_hash << 16) ^ ((b << 11) ^ m_hash);
         m_hash += m_hash >> 11;
     }

     void addCharacter(UChar character)
     {
         if (m_hasPendingCharacter) {
             m_hasPendingCharacter = false;
             addCharactersAssumingAligned(m_pendingCharacter, character);
             return;
         }

         m_pendingCharacter = character;
         m_hasPendingCharacter = true;
     }

     void addCharacters(UChar a, UChar b)
     {
         if (m_hasPendingCharacter) {
 #if ENABLE(ASSERT)
             m_hasPendingCharacter = false;
 #endif
             addCharactersAssumingAligned(m_pendingCharacter, a);
             m_pendingCharacter = b;
 #if ENABLE(ASSERT)
             m_hasPendingCharacter = true;
 #endif
             return;
         }

         addCharactersAssumingAligned(a, b);
     }

     template<typename T, UChar Converter(T)> void addCharactersAssumingAligned(const T* data, unsigned length)
     {
         ASSERT(!m_hasPendingCharacter);

         bool remainder = length & 1;
         length >>= 1;

         while (length--) {
             addCharactersAssumingAligned(Converter(data[0]), Converter(data[1]));
             data += 2;
         }

         if (remainder)
             addCharacter(Converter(*data));
     }

     template<typename T> void addCharactersAssumingAligned(const T* data, unsigned length)
     {
         addCharactersAssumingAligned<T, defaultConverter>(data, length);
     }

     template<typename T, UChar Converter(T)> void addCharacters(const T* data, unsigned length)
     {
         if (m_hasPendingCharacter && length) {
             m_hasPendingCharacter = false;
             addCharactersAssumingAligned(m_pendingCharacter, Converter(*data++));
             --length;
         }
         addCharactersAssumingAligned<T, Converter>(data, length);
     }

     template<typename T> void addCharacters(const T* data, unsigned length)
     {
         addCharacters<T, defaultConverter>(data, length);
     }

     unsigned hashWithTop8BitsMasked() const
     {
         unsigned result = avalancheBits();

         // Reserving space from the high bits for flags preserves most of the hash's
         // value, since hash lookup typically masks out the high bits anyway.
         result &= (1U << (sizeof(result) * 8 - flagCount)) - 1;

         // This avoids ever returning a hash code of 0, since that is used to
         // signal "hash not computed yet". Setting the high bit maintains
         // reasonable fidelity to a hash code of 0 because it is likely to yield
         // exactly 0 when hash lookup masks out the high bits.
         if (!result)
             result = 0x80000000 >> flagCount;

         return result;
     }

     unsigned hash() const
     {
         unsigned result = avalancheBits();

         // This avoids ever returning a hash code of 0, since that is used to
         // signal "hash not computed yet". Setting the high bit maintains
         // reasonable fidelity to a hash code of 0 because it is likely to yield
         // exactly 0 when hash lookup masks out the high bits.
         if (!result)
             result = 0x80000000;

         return result;
     }

     template<typename T, UChar Converter(T)> static unsigned computeHashAndMaskTop8Bits(const T* data, unsigned length)
     {
         StringHasher hasher;
         hasher.addCharactersAssumingAligned<T, Converter>(data, length);
         return hasher.hashWithTop8BitsMasked();
     }

     template<typename T> static unsigned computeHashAndMaskTop8Bits(const T* data, unsigned length)
     {
         return computeHashAndMaskTop8Bits<T, defaultConverter>(data, length);
     }

     template<typename T, UChar Converter(T)> static unsigned computeHash(const T* data, unsigned length)
     {
         StringHasher hasher;
         hasher.addCharactersAssumingAligned<T, Converter>(data, length);
         return hasher.hash();
     }

     template<typename T> static unsigned computeHash(const T* data, unsigned length)
     {
         return computeHash<T, defaultConverter>(data, length);
     }

     static unsigned hashMemory(const void* data, unsigned length)
     {
         // FIXME: Why does this function use the version of the hash that drops the top 8 bits?
         // We want that for all string hashing so we can use those bits in StringImpl and hash
         // strings consistently, but I don't see why we'd want that for general memory hashing.
         ASSERT(!(length % 2));
         return computeHashAndMaskTop8Bits<UChar>(static_cast<const UChar*>(data), length / sizeof(UChar));
     }

     template<size_t length> static unsigned hashMemory(const void* data)
     {
         static_assert(!(length % 2), "length must be a multiple of two");
         return hashMemory(data, length);
     }

 private:
     static UChar defaultConverter(UChar character)
     {
         return character;
     }

     static UChar defaultConverter(LChar character)
     {
         return character;
     }

     unsigned avalancheBits() const
     {
         unsigned result = m_hash;

         // Handle end case.
         if (m_hasPendingCharacter) {
             result += m_pendingCharacter;
             result ^= result << 11;
             result += result >> 17;
         }

         // Force "avalanching" of final 31 bits.
         result ^= result << 3;
         result += result >> 5;
         result ^= result << 2;
         result += result >> 15;
         result ^= result << 10;

         return result;
     }

     unsigned m_hash;
     bool m_hasPendingCharacter;
     UChar m_pendingCharacter;
 };

 } // namespace WTF

 using WTF::StringHasher;

 #endif // WTF_StringHasher_h
	/*
	* Copyright (C) 2005, 2006, 2008, 2010, 2013 Apple Inc. All rights reserved.
	* Copyright (C) 2010 Patrick Gansterer <paroga@paroga.com>
	*
	* 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.
	*
	*/

	#ifndef WTF_StringHasher_h
	#define WTF_StringHasher_h

	#include "wtf/text/Unicode.h"

	namespace WTF {

	// Paul Hsieh's SuperFastHash
	// http://www.azillionmonkeys.com/qed/hash.html

	// LChar data is interpreted as Latin-1-encoded (zero extended to 16 bits).

	// NOTE: The hash computation here must stay in sync with the create_hash_table script in
	// JavaScriptCore and the CodeGeneratorJS.pm script in WebCore.

	// Golden ratio. Arbitrary start value to avoid mapping all zeros to a hash value of zero.
	static const unsigned stringHashingStartValue = 0x9E3779B9U;

	class StringHasher {
	public:
	static const unsigned flagCount = 8; // Save 8 bits for StringImpl to use as flags.

	StringHasher()
	: m_hash(stringHashingStartValue)
	, m_hasPendingCharacter(false)
	, m_pendingCharacter(0)
	{
	}

	// The hasher hashes two characters at a time, and thus an "aligned" hasher is one
	// where an even number of characters have been added. Callers that always add
	// characters two at a time can use the "assuming aligned" functions.
	void addCharactersAssumingAligned(UChar a, UChar b)
	{
	ASSERT(!m_hasPendingCharacter);
	m_hash += a;
	m_hash = (m_hash << 16) ^ ((b << 11) ^ m_hash);
	m_hash += m_hash >> 11;
	}

	void addCharacter(UChar character)
	{
	if (m_hasPendingCharacter) {
	m_hasPendingCharacter = false;
	addCharactersAssumingAligned(m_pendingCharacter, character);
	return;
	}

	m_pendingCharacter = character;
	m_hasPendingCharacter = true;
	}

	void addCharacters(UChar a, UChar b)
	{
	if (m_hasPendingCharacter) {
	#if ENABLE(ASSERT)
	m_hasPendingCharacter = false;
	#endif
	addCharactersAssumingAligned(m_pendingCharacter, a);
	m_pendingCharacter = b;
	#if ENABLE(ASSERT)
	m_hasPendingCharacter = true;
	#endif
	return;
	}

	addCharactersAssumingAligned(a, b);
	}

	template<typename T, UChar Converter(T)> void addCharactersAssumingAligned(const T* data, unsigned length)
	{
	ASSERT(!m_hasPendingCharacter);

	bool remainder = length & 1;
	length >>= 1;

	while (length--) {
	addCharactersAssumingAligned(Converter(data[0]), Converter(data[1]));
	data += 2;
	}

	if (remainder)
	addCharacter(Converter(*data));
	}

	template<typename T> void addCharactersAssumingAligned(const T* data, unsigned length)
	{
	addCharactersAssumingAligned<T, defaultConverter>(data, length);
	}

	template<typename T, UChar Converter(T)> void addCharacters(const T* data, unsigned length)
	{
	if (m_hasPendingCharacter && length) {
	m_hasPendingCharacter = false;
	addCharactersAssumingAligned(m_pendingCharacter, Converter(*data++));
	--length;
	}
	addCharactersAssumingAligned<T, Converter>(data, length);
	}

	template<typename T> void addCharacters(const T* data, unsigned length)
	{
	addCharacters<T, defaultConverter>(data, length);
	}

	unsigned hashWithTop8BitsMasked() const
	{
	unsigned result = avalancheBits();

	// Reserving space from the high bits for flags preserves most of the hash's
	// value, since hash lookup typically masks out the high bits anyway.
	result &= (1U << (sizeof(result) * 8 - flagCount)) - 1;

	// This avoids ever returning a hash code of 0, since that is used to
	// signal "hash not computed yet". Setting the high bit maintains
	// reasonable fidelity to a hash code of 0 because it is likely to yield
	// exactly 0 when hash lookup masks out the high bits.
	if (!result)
	result = 0x80000000 >> flagCount;

	return result;
	}

	unsigned hash() const
	{
	unsigned result = avalancheBits();

	// This avoids ever returning a hash code of 0, since that is used to
	// signal "hash not computed yet". Setting the high bit maintains
	// reasonable fidelity to a hash code of 0 because it is likely to yield
	// exactly 0 when hash lookup masks out the high bits.
	if (!result)
	result = 0x80000000;

	return result;
	}

	template<typename T, UChar Converter(T)> static unsigned computeHashAndMaskTop8Bits(const T* data, unsigned length)
	{
	StringHasher hasher;
	hasher.addCharactersAssumingAligned<T, Converter>(data, length);
	return hasher.hashWithTop8BitsMasked();
	}

	template<typename T> static unsigned computeHashAndMaskTop8Bits(const T* data, unsigned length)
	{
	return computeHashAndMaskTop8Bits<T, defaultConverter>(data, length);
	}

	template<typename T, UChar Converter(T)> static unsigned computeHash(const T* data, unsigned length)
	{
	StringHasher hasher;
	hasher.addCharactersAssumingAligned<T, Converter>(data, length);
	return hasher.hash();
	}

	template<typename T> static unsigned computeHash(const T* data, unsigned length)
	{
	return computeHash<T, defaultConverter>(data, length);
	}

	static unsigned hashMemory(const void* data, unsigned length)
	{
	// FIXME: Why does this function use the version of the hash that drops the top 8 bits?
	// We want that for all string hashing so we can use those bits in StringImpl and hash
	// strings consistently, but I don't see why we'd want that for general memory hashing.
	ASSERT(!(length % 2));
	return computeHashAndMaskTop8Bits<UChar>(static_cast<const UChar*>(data), length / sizeof(UChar));
	}

	template<size_t length> static unsigned hashMemory(const void* data)
	{
	static_assert(!(length % 2), "length must be a multiple of two");
	return hashMemory(data, length);
	}

	private:
	static UChar defaultConverter(UChar character)
	{
	return character;
	}

	static UChar defaultConverter(LChar character)
	{
	return character;
	}

	unsigned avalancheBits() const
	{
	unsigned result = m_hash;

	// Handle end case.
	if (m_hasPendingCharacter) {
	result += m_pendingCharacter;
	result ^= result << 11;
	result += result >> 17;
	}

	// Force "avalanching" of final 31 bits.
	result ^= result << 3;
	result += result >> 5;
	result ^= result << 2;
	result += result >> 15;
	result ^= result << 10;

	return result;
	}

	unsigned m_hash;
	bool m_hasPendingCharacter;
	UChar m_pendingCharacter;
	};

	} // namespace WTF

	using WTF::StringHasher;

	#endif // WTF_StringHasher_h