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/*
* 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 SKY_ENGINE_WTF_STRINGHASHER_H_
#define SKY_ENGINE_WTF_STRINGHASHER_H_
#include "sky/engine/wtf/unicode/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)
{
COMPILE_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 // SKY_ENGINE_WTF_STRINGHASHER_H_