1 /*

     2  * Copyright (C) 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.

     3  *

     4  * This library is free software; you can redistribute it and/or

     5  * modify it under the terms of the GNU Library General Public

     6  * License as published by the Free Software Foundation; either

     7  * version 2 of the License, or (at your option) any later version.

     8  *

     9  * This library is distributed in the hope that it will be useful,

    10  * but WITHOUT ANY WARRANTY; without even the implied warranty of

    11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

    12  * Library General Public License for more details.

    13  *

    14  * You should have received a copy of the GNU Library General Public License

    15  * along with this library; see the file COPYING.LIB.  If not, write to

    16  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,

    17  * Boston, MA 02110-1301, USA.

    18  *

    19  */

    20 

    21 #ifndef WTF_HashTraits_h

    22 #define WTF_HashTraits_h

    23 

    24 #include "HashFunctions.h"

    25 #include "TypeTraits.h"

    26 #include <utility>

    27 #include <limits>

    28 

    29 namespace WTF {

    30 

    31     using std::pair;

    32     using std::make_pair;

    33 

    34     template<typename T> struct HashTraits;

    35 

    36     template<bool isInteger, typename T> struct GenericHashTraitsBase;

    37 

    38     template<typename T> struct GenericHashTraitsBase<false, T> {

    39         static const bool emptyValueIsZero = false;

    40         static const bool needsDestruction = true;

    41     };

    42 

    43     // Default integer traits disallow both 0 and -1 as keys (max value instead of -1 for unsigned).

    44     template<typename T> struct GenericHashTraitsBase<true, T> {

    45         static const bool emptyValueIsZero = true;

    46         static const bool needsDestruction = false;

    47         static void constructDeletedValue(T& slot) { slot = static_cast<T>(-1); }

    48         static bool isDeletedValue(T value) { return value == static_cast<T>(-1); }

    49     };

    50 

    51     template<typename T> struct GenericHashTraits : GenericHashTraitsBase<IsInteger<T>::value, T> {

    52         typedef T TraitType;

    53         static T emptyValue() { return T(); }

    54     };

    55 

    56     template<typename T> struct HashTraits : GenericHashTraits<T> { };

    57 

    58     template<typename T> struct FloatHashTraits : GenericHashTraits<T> {

    59         static const bool needsDestruction = false;

    60         static T emptyValue() { return std::numeric_limits<T>::infinity(); }

    61         static void constructDeletedValue(T& slot) { slot = -std::numeric_limits<T>::infinity(); }

    62         static bool isDeletedValue(T value) { return value == -std::numeric_limits<T>::infinity(); }

    63     };

    64 

    65     template<> struct HashTraits<float> : FloatHashTraits<float> { };

    66     template<> struct HashTraits<double> : FloatHashTraits<double> { };

    67 

    68     // Default unsigned traits disallow both 0 and max as keys -- use these traits to allow zero and disallow max - 1.

    69     template<typename T> struct UnsignedWithZeroKeyHashTraits : GenericHashTraits<T> {

    70         static const bool emptyValueIsZero = false;

    71         static const bool needsDestruction = false;

    72         static T emptyValue() { return std::numeric_limits<T>::max(); }

    73         static void constructDeletedValue(T& slot) { slot = std::numeric_limits<T>::max() - 1; }

    74         static bool isDeletedValue(T value) { return value == std::numeric_limits<T>::max() - 1; }

    75     };

    76 

    77     template<typename P> struct HashTraits<P*> : GenericHashTraits<P*> {

    78         static const bool emptyValueIsZero = true;

    79         static const bool needsDestruction = false;

    80         static void constructDeletedValue(P*& slot) { slot = reinterpret_cast<P*>(-1); }

    81         static bool isDeletedValue(P* value) { return value == reinterpret_cast<P*>(-1); }

    82     };

    83 

    84     template<typename P> struct HashTraits<RefPtr<P> > : GenericHashTraits<RefPtr<P> > {

    85         static const bool emptyValueIsZero = true;

    86         static void constructDeletedValue(RefPtr<P>& slot) { new (&slot) RefPtr<P>(HashTableDeletedValue); }

    87         static bool isDeletedValue(const RefPtr<P>& value) { return value.isHashTableDeletedValue(); }

    88     };

    89 

    90     // special traits for pairs, helpful for their use in HashMap implementation

    91 

    92     template<typename FirstTraitsArg, typename SecondTraitsArg>

    93     struct PairHashTraits : GenericHashTraits<pair<typename FirstTraitsArg::TraitType, typename SecondTraitsArg::TraitType> > {

    94         typedef FirstTraitsArg FirstTraits;

    95         typedef SecondTraitsArg SecondTraits;

    96         typedef pair<typename FirstTraits::TraitType, typename SecondTraits::TraitType> TraitType;

    97 

    98         static const bool emptyValueIsZero = FirstTraits::emptyValueIsZero && SecondTraits::emptyValueIsZero;

    99         static TraitType emptyValue() { return make_pair(FirstTraits::emptyValue(), SecondTraits::emptyValue()); }

   100 

   101         static const bool needsDestruction = FirstTraits::needsDestruction || SecondTraits::needsDestruction;

   102 

   103         static void constructDeletedValue(TraitType& slot) { FirstTraits::constructDeletedValue(slot.first); }

   104         static bool isDeletedValue(const TraitType& value) { return FirstTraits::isDeletedValue(value.first); }

   105     };

   106 

   107     template<typename First, typename Second>

   108     struct HashTraits<pair<First, Second> > : public PairHashTraits<HashTraits<First>, HashTraits<Second> > { };

   109 

   110 } // namespace WTF

   111 

   112 using WTF::HashTraits;

   113 using WTF::PairHashTraits;

   114 

   115 #endif // WTF_HashTraits_h