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
29namespace 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
112using WTF::HashTraits;
113using WTF::PairHashTraits;
114
115#endif // WTF_HashTraits_h
116