wtf/HashTraits.h

   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