hash_tables.h revision 21d179b334e59e9a3bfcaed4c4430bef1bc5759d 
1// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4//
5
6//
7// Deal with the differences between Microsoft and GNU implemenations
8// of hash_map. Allows all platforms to use |base::hash_map| and
9// |base::hash_set|.
10//  eg:
11//   base::hash_map<int> my_map;
12//   base::hash_set<int> my_set;
13//
14// NOTE: It is an explicit non-goal of this class to provide a generic hash
15// function for pointers.  If you want to hash a pointers to a particular class,
16// please define the template specialization elsewhere (for example, in its
17// header file) and keep it specific to just pointers to that class.  This is
18// because identity hashes are not desirable for all types that might show up
19// in containers as pointers.
20
21#ifndef BASE_HASH_TABLES_H_
22#define BASE_HASH_TABLES_H_
23#pragma once
24
25#include "build/build_config.h"
26
27#include "base/string16.h"
28
29#if defined(COMPILER_MSVC)
30#include <hash_map>
31#include <hash_set>
32namespace base {
33using stdext::hash_map;
34using stdext::hash_set;
35}
36#elif defined(COMPILER_GCC)
37// This is a hack to disable the gcc 4.4 warning about hash_map and hash_set
38// being deprecated.  We can get rid of this when we upgrade to VS2008 and we
39// can use <tr1/unordered_map> and <tr1/unordered_set>.
40#ifdef __DEPRECATED
41#define CHROME_OLD__DEPRECATED __DEPRECATED
42#undef __DEPRECATED
43#endif
44
45#include <ext/hash_map>
46#include <ext/hash_set>
47#include <string>
48
49#ifdef CHROME_OLD__DEPRECATED
50#define __DEPRECATED CHROME_OLD__DEPRECATED
51#undef CHROME_OLD__DEPRECATED
52#endif
53
54namespace base {
55using __gnu_cxx::hash_map;
56using __gnu_cxx::hash_set;
57}  // namespace base
58
59namespace __gnu_cxx {
60
61<<<<<<< HEAD
62#ifndef ANDROID
63// Already defined for android
64
65// The GNU C++ library provides identiy hash functions for many integral types,
66=======
67// The GNU C++ library provides identity hash functions for many integral types,
68>>>>>>> chromium.org at r10.0.621.0
69// but not for |long long|.  This hash function will truncate if |size_t| is
70// narrower than |long long|.  This is probably good enough for what we will
71// use it for.
72
73#define DEFINE_TRIVIAL_HASH(integral_type) \
74    template<> \
75    struct hash<integral_type> { \
76      std::size_t operator()(integral_type value) const { \
77        return static_cast<std::size_t>(value); \
78      } \
79    }
80
81DEFINE_TRIVIAL_HASH(long long);
82DEFINE_TRIVIAL_HASH(unsigned long long);
83
84#undef DEFINE_TRIVIAL_HASH
85#endif
86
87// Implement string hash functions so that strings of various flavors can
88// be used as keys in STL maps and sets.  The hash algorithm comes from the
89// GNU C++ library, in <tr1/functional>.  It is duplicated here because GCC
90// versions prior to 4.3.2 are unable to compile <tr1/functional> when RTTI
91// is disabled, as it is in our build.
92
93#define DEFINE_STRING_HASH(string_type) \
94    template<> \
95    struct hash<string_type> { \
96      std::size_t operator()(const string_type& s) const { \
97        std::size_t result = 0; \
98        for (string_type::const_iterator i = s.begin(); i != s.end(); ++i) \
99          result = (result * 131) + *i; \
100        return result; \
101      } \
102    }
103
104DEFINE_STRING_HASH(std::string);
105DEFINE_STRING_HASH(std::wstring);
106
107#if defined(WCHAR_T_IS_UTF32)
108// If string16 and std::wstring are not the same type, provide a
109// specialization for string16.
110DEFINE_STRING_HASH(string16);
111#endif  // WCHAR_T_IS_UTF32
112
113#undef DEFINE_STRING_HASH
114
115}  // namespace __gnu_cxx
116
117#endif  // COMPILER
118
119#endif  // BASE_HASH_TABLES_H_
120