Move Source/WTF/wtf to Source/wtf

Source/WTF/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/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 !ASSERT_DISABLED
-            m_hasPendingCharacter = false;
-#endif
-            addCharactersAssumingAligned(m_pendingCharacter, a);
-            m_pendingCharacter = b;
-#if !ASSERT_DISABLED
-            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 addCharactersAssumingAligned(const T* data)
-    {
-        ASSERT(!m_hasPendingCharacter);
-
-        while (T a = *data++) {
-            T b = *data++;
-            if (!b) {
-                addCharacter(Converter(a));
-                break;
-            }
-            addCharactersAssumingAligned(Converter(a), Converter(b));
-        }
-    }
-
-    template<typename T> void addCharactersAssumingAligned(const T* data)
-    {
-        addCharactersAssumingAligned<T, defaultConverter>(data);
-    }
-
-    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);
-    }
-
-    template<typename T, UChar Converter(T)> void addCharacters(const T* data)
-    {
-        if (m_hasPendingCharacter && *data) {
-            m_hasPendingCharacter = false;
-            addCharactersAssumingAligned(m_pendingCharacter, Converter(*data++));
-        }
-        addCharactersAssumingAligned<T, Converter>(data);
-    }
-
-    template<typename T> void addCharacters(const T* data)
-    {
-        addCharacters<T, defaultConverter>(data);
-    }
-
-    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, UChar Converter(T)> static unsigned computeHashAndMaskTop8Bits(const T* data)
-    {
-        StringHasher hasher;
-        hasher.addCharactersAssumingAligned<T, Converter>(data);
-        return hasher.hashWithTop8BitsMasked();
-    }
-
-    template<typename T> static unsigned computeHashAndMaskTop8Bits(const T* data, unsigned length)
-    {
-        return computeHashAndMaskTop8Bits<T, defaultConverter>(data, length);
-    }
-
-    template<typename T> static unsigned computeHashAndMaskTop8Bits(const T* data)
-    {
-        return computeHashAndMaskTop8Bits<T, defaultConverter>(data);
-    }
-
-    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, UChar Converter(T)> static unsigned computeHash(const T* data)
-    {
-        StringHasher hasher;
-        hasher.addCharactersAssumingAligned<T, Converter>(data);
-        return hasher.hash();
-    }
-
-    template<typename T> static unsigned computeHash(const T* data, unsigned length)
-    {
-        return computeHash<T, defaultConverter>(data, length);
-    }
-
-    template<typename T> static unsigned computeHash(const T* data)
-    {
-        return computeHash<T, defaultConverter>(data);
-    }
-
-    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 // WTF_StringHasher_h