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	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 T> struct SimpleClassHashTraits : GenericHashTraits<T> {
	85	static const bool emptyValueIsZero = true;
	86	static void constructDeletedValue(T& slot) { new (&slot) T(HashTableDeletedValue); }
	87	static bool isDeletedValue(const T& value) { return value.isHashTableDeletedValue(); }
	88	};
	89
	90	template<typename P> struct HashTraits<RefPtr<P> > : SimpleClassHashTraits<RefPtr<P> > { };
	91
	92	// special traits for pairs, helpful for their use in HashMap implementation
	93
	94	template<typename FirstTraitsArg, typename SecondTraitsArg>
	95	struct PairHashTraits : GenericHashTraits<pair<typename FirstTraitsArg::TraitType, typename SecondTraitsArg::TraitType> > {
	96	typedef FirstTraitsArg FirstTraits;
	97	typedef SecondTraitsArg SecondTraits;
	98	typedef pair<typename FirstTraits::TraitType, typename SecondTraits::TraitType> TraitType;
	99
	100	static const bool emptyValueIsZero = FirstTraits::emptyValueIsZero && SecondTraits::emptyValueIsZero;
	101	static TraitType emptyValue() { return make_pair(FirstTraits::emptyValue(), SecondTraits::emptyValue()); }
	102
	103	static const bool needsDestruction = FirstTraits::needsDestruction \|\| SecondTraits::needsDestruction;
	104
	105	static void constructDeletedValue(TraitType& slot) { FirstTraits::constructDeletedValue(slot.first); }
	106	static bool isDeletedValue(const TraitType& value) { return FirstTraits::isDeletedValue(value.first); }
	107	};
	108
	109	template<typename First, typename Second>
	110	struct HashTraits<pair<First, Second> > : public PairHashTraits<HashTraits<First>, HashTraits<Second> > { };
	111
	112	} // namespace WTF
	113
	114	using WTF::HashTraits;
	115	using WTF::PairHashTraits;
	116
	117	#endif // WTF_HashTraits_h