/*

 * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved

 * Copyright (C) Research In Motion Limited 2009. 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.

 *

 */

#ifndef StringHash_h

#define StringHash_h

#include "AtomicString.h"

#include "WTFString.h"

#include <wtf/HashTraits.h>

#include <wtf/StringHashFunctions.h>

#include <wtf/unicode/Unicode.h>

// FIXME: This is a temporary layering violation while we move string code to WTF.

// Landing the file moves in one patch, will follow on with patches to change the namespaces.

namespace WebCore {

    // The hash() functions on StringHash and CaseFoldingHash do not support

    // null strings. get(), contains(), and add() on HashMap<String,..., StringHash>

    // cause a null-pointer dereference when passed null strings.

    // FIXME: We should really figure out a way to put the computeHash function that's

    // currently a member function of StringImpl into this file so we can be a little

    // closer to having all the nearly-identical hash functions in one place.

    struct StringHash {

        static unsigned hash(StringImpl* key) { return key->hash(); }

        static bool equal(const StringImpl* a, const StringImpl* b)

        {

            if (a == b)

                return true;

            if (!a || !b)

                return false;

            unsigned aLength = a->length();

            unsigned bLength = b->length();

            if (aLength != bLength)

                return false;

            // FIXME: perhaps we should have a more abstract macro that indicates when

            // going 4 bytes at a time is unsafe

#if CPU(ARM) || CPU(SH4)

            const UChar* aChars = a->characters();

            const UChar* bChars = b->characters();

            for (unsigned i = 0; i != aLength; ++i) {

                if (*aChars++ != *bChars++)

                    return false;

            }

            return true;

#else

            /* Do it 4-bytes-at-a-time on architectures where it's safe */

            const uint32_t* aChars = reinterpret_cast<const uint32_t*>(a->characters());

            const uint32_t* bChars = reinterpret_cast<const uint32_t*>(b->characters());

            unsigned halfLength = aLength >> 1;

            for (unsigned i = 0; i != halfLength; ++i)

                if (*aChars++ != *bChars++)

                    return false;

            if (aLength & 1 && *reinterpret_cast<const uint16_t*>(aChars) != *reinterpret_cast<const uint16_t*>(bChars))

                return false;

            return true;

#endif

        }

        static unsigned hash(const RefPtr<StringImpl>& key) { return key->hash(); }

        static bool equal(const RefPtr<StringImpl>& a, const RefPtr<StringImpl>& b)

        {

            return equal(a.get(), b.get());

        }

        static unsigned hash(const String& key) { return key.impl()->hash(); }

        static bool equal(const String& a, const String& b)

        {

            return equal(a.impl(), b.impl());

        }

        static const bool safeToCompareToEmptyOrDeleted = false;

    };

    class CaseFoldingHash {

    public:

        // Paul Hsieh's SuperFastHash

        // http://www.azillionmonkeys.com/qed/hash.html

        static unsigned hash(const UChar* data, unsigned length)

        {

            unsigned l = length;

            const UChar* s = data;

            uint32_t hash = WTF::stringHashingStartValue;

            uint32_t tmp;

            int rem = l & 1;

            l >>= 1;

            // Main loop.

            for (; l > 0; l--) {

                hash += WTF::Unicode::foldCase(s[0]);

                tmp = (WTF::Unicode::foldCase(s[1]) << 11) ^ hash;

                hash = (hash << 16) ^ tmp;

                s += 2;

                hash += hash >> 11;

            }

            // Handle end case.

            if (rem) {

                hash += WTF::Unicode::foldCase(s[0]);

                hash ^= hash << 11;

                hash += hash >> 17;

            }

            // Force "avalanching" of final 127 bits.

            hash ^= hash << 3;

            hash += hash >> 5;

            hash ^= hash << 2;

            hash += hash >> 15;

            hash ^= hash << 10;

            // 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.

            hash |= !hash << 31;

            return hash;

        }

        static unsigned hash(StringImpl* str)

        {

            return hash(str->characters(), str->length());

        }

        static unsigned hash(const char* str, unsigned length)

        {

            // This hash is designed to work on 16-bit chunks at a time. But since the normal case

            // (above) is to hash UTF-16 characters, we just treat the 8-bit chars as if they

            // were 16-bit chunks, which will give matching results.

            unsigned l = length;

            const char* s = str;

            uint32_t hash = WTF::stringHashingStartValue;

            uint32_t tmp;

            int rem = l & 1;

            l >>= 1;

            // Main loop

            for (; l > 0; l--) {

                hash += WTF::Unicode::foldCase(s[0]);

                tmp = (WTF::Unicode::foldCase(s[1]) << 11) ^ hash;

                hash = (hash << 16) ^ tmp;

                s += 2;

                hash += hash >> 11;

            }

            // Handle end case

            if (rem) {

                hash += WTF::Unicode::foldCase(s[0]);

                hash ^= hash << 11;

                hash += hash >> 17;

            }

            // Force "avalanching" of final 127 bits

            hash ^= hash << 3;

            hash += hash >> 5;

            hash ^= hash << 2;

            hash += hash >> 15;

            hash ^= hash << 10;

            // 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

            hash |= !hash << 31;

            return hash;

        }

        static bool equal(const StringImpl* a, const StringImpl* b)

        {

            if (a == b)

                return true;

            if (!a || !b)

                return false;

            unsigned length = a->length();

            if (length != b->length())

                return false;

            return WTF::Unicode::umemcasecmp(a->characters(), b->characters(), length) == 0;

        }

        static unsigned hash(const RefPtr<StringImpl>& key) 

        {

            return hash(key.get());

        }

        static bool equal(const RefPtr<StringImpl>& a, const RefPtr<StringImpl>& b)

        {

            return equal(a.get(), b.get());

        }

        static unsigned hash(const String& key)

        {

            return hash(key.impl());

        }

        static unsigned hash(const AtomicString& key)

        {

            return hash(key.impl());

        }

        static bool equal(const String& a, const String& b)

        {

            return equal(a.impl(), b.impl());

        }

        static bool equal(const AtomicString& a, const AtomicString& b)

        {

            return (a == b) || equal(a.impl(), b.impl());

        }

        static const bool safeToCompareToEmptyOrDeleted = false;

    };

    // This hash can be used in cases where the key is a hash of a string, but we don't

    // want to store the string. It's not really specific to string hashing, but all our

    // current uses of it are for strings.

    struct AlreadyHashed : IntHash<unsigned> {

        static unsigned hash(unsigned key) { return key; }

        // To use a hash value as a key for a hash table, we need to eliminate the

        // "deleted" value, which is negative one. That could be done by changing

        // the string hash function to never generate negative one, but this works

        // and is still relatively efficient.

        static unsigned avoidDeletedValue(unsigned hash)

        {

            ASSERT(hash);

            unsigned newHash = hash | (!(hash + 1) << 31);

            ASSERT(newHash);

            ASSERT(newHash != 0xFFFFFFFF);

            return newHash;

        }

    };

}

namespace WTF {

    template<> struct HashTraits<WebCore::String> : GenericHashTraits<WebCore::String> {

        static const bool emptyValueIsZero = true;

        static void constructDeletedValue(WebCore::String& slot) { new (&slot) WebCore::String(HashTableDeletedValue); }

        static bool isDeletedValue(const WebCore::String& slot) { return slot.isHashTableDeletedValue(); }

    };

}

#endif