JavaScriptCore-903.tar.gz

[apple/javascriptcore.git] / wtf / StringHasher.h

diff --git a/wtf/StringHasher.h b/wtf/StringHasher.h
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+/*
+ * Copyright (C) 2005, 2006, 2008, 2010 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 {
+
+// Golden ratio - arbitrary start value to avoid mapping all 0's to all 0's
+static const unsigned stringHashingStartValue = 0x9e3779b9U;
+
+// Paul Hsieh's SuperFastHash
+// http://www.azillionmonkeys.com/qed/hash.html
+// char* data is interpreted as latin-encoded (zero extended to 16 bits).
+class StringHasher {
+public:
+    inline StringHasher()
+        : m_hash(stringHashingStartValue)
+        , m_hasPendingCharacter(false)
+        , m_pendingCharacter(0)
+    {
+    }
+
+    inline void addCharacters(UChar a, UChar b)
+    {
+        ASSERT(!m_hasPendingCharacter);
+        addCharactersToHash(a, b);
+    }
+
+    inline void addCharacter(UChar ch)
+    {
+        if (m_hasPendingCharacter) {
+            addCharactersToHash(m_pendingCharacter, ch);
+            m_hasPendingCharacter = false;
+            return;
+        }
+
+        m_pendingCharacter = ch;
+        m_hasPendingCharacter = true;
+    }
+
+    inline unsigned hash() 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;
+
+        // First bit is used in UStringImpl for m_isIdentifier.
+        result &= 0x7fffffff;
+
+        // This avoids ever returning a hash code of 0, since that is used to
+        // signal "hash not computed yet", using a value that is likely to be
+        // effectively the same as 0 when the low bits are masked.
+        if (!result)
+            return 0x40000000;
+
+        return result;
+    }
+
+    template<typename T, UChar Converter(T)> static inline unsigned computeHash(const T* data, unsigned length)
+    {
+        StringHasher hasher;
+        bool rem = length & 1;
+        length >>= 1;
+
+        while (length--) {
+            hasher.addCharacters(Converter(data[0]), Converter(data[1]));
+            data += 2;
+        }
+
+        if (rem)
+            hasher.addCharacter(Converter(*data));
+
+        return hasher.hash();
+    }
+
+    template<typename T, UChar Converter(T)> static inline unsigned computeHash(const T* data)
+    {
+        StringHasher hasher;
+
+        while (true) {
+            UChar b0 = Converter(*data++);
+            if (!b0)
+                break;
+            UChar b1 = Converter(*data++);
+            if (!b1) {
+                hasher.addCharacter(b0);
+                break;
+            }
+
+            hasher.addCharacters(b0, b1);
+        }
+
+        return hasher.hash();
+    }
+
+    template<typename T> static inline unsigned computeHash(const T* data, unsigned length)
+    {
+        return computeHash<T, defaultCoverter>(data, length);
+    }
+
+    template<typename T> static inline unsigned computeHash(const T* data)
+    {
+        return computeHash<T, defaultCoverter>(data);
+    }
+
+    template<size_t length> static inline unsigned hashMemory(const void* data)
+    {
+        COMPILE_ASSERT(!(length % 4), length_must_be_a_multible_of_four);
+        return computeHash<UChar>(static_cast<const UChar*>(data), length / sizeof(UChar));
+    }
+
+    static inline unsigned hashMemory(const void* data, unsigned size)
+    {
+        ASSERT(!(size % 2));
+        return computeHash<UChar>(static_cast<const UChar*>(data), size / sizeof(UChar));
+    }
+
+private:
+    static inline UChar defaultCoverter(UChar ch)
+    {
+        return ch;
+    }
+
+    static inline UChar defaultCoverter(char ch)
+    {
+        return static_cast<unsigned char>(ch);
+    }
+
+    inline void addCharactersToHash(UChar a, UChar b)
+    {
+        m_hash += a;
+        unsigned tmp = (b << 11) ^ m_hash;
+        m_hash = (m_hash << 16) ^ tmp;
+        m_hash += m_hash >> 11;
+    }
+
+    unsigned m_hash;
+    bool m_hasPendingCharacter;
+    UChar m_pendingCharacter;
+};
+
+} // namespace WTF
+
+using WTF::StringHasher;
+
+#endif // WTF_StringHasher_h