hash_tables.h revision 5e3f23d412006dc4db4e659864679f29341e113f 
1// Copyright (c) 2011 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_CONTAINERS_HASH_TABLES_H_
22#define BASE_CONTAINERS_HASH_TABLES_H_
23
24#include "base/strings/string16.h"
25#include "build/build_config.h"
26
27#if defined(COMPILER_MSVC)
28#include <hash_map>
29#include <hash_set>
30
31#define BASE_HASH_NAMESPACE stdext
32
33#elif defined(COMPILER_GCC)
34#if defined(OS_ANDROID)
35#define BASE_HASH_NAMESPACE std
36#else
37#define BASE_HASH_NAMESPACE __gnu_cxx
38#endif
39
40// This is a hack to disable the gcc 4.4 warning about hash_map and hash_set
41// being deprecated.  We can get rid of this when we upgrade to VS2008 and we
42// can use <tr1/unordered_map> and <tr1/unordered_set>.
43#ifdef __DEPRECATED
44#define CHROME_OLD__DEPRECATED __DEPRECATED
45#undef __DEPRECATED
46#endif
47
48#if defined(OS_ANDROID)
49#include <hash_map>
50#include <hash_set>
51#else
52#include <ext/hash_map>
53#include <ext/hash_set>
54#endif
55
56#include <string>
57
58#ifdef CHROME_OLD__DEPRECATED
59#define __DEPRECATED CHROME_OLD__DEPRECATED
60#undef CHROME_OLD__DEPRECATED
61#endif
62
63namespace BASE_HASH_NAMESPACE {
64
65#if !defined(OS_ANDROID)
66// The GNU C++ library provides identity hash functions for many integral types,
67// but not for |long long|.  This hash function will truncate if |size_t| is
68// narrower than |long long|.  This is probably good enough for what we will
69// use it for.
70
71#define DEFINE_TRIVIAL_HASH(integral_type) \
72    template<> \
73    struct hash<integral_type> { \
74      std::size_t operator()(integral_type value) const { \
75        return static_cast<std::size_t>(value); \
76      } \
77    }
78
79DEFINE_TRIVIAL_HASH(long long);
80DEFINE_TRIVIAL_HASH(unsigned long long);
81
82#undef DEFINE_TRIVIAL_HASH
83#endif  // !defined(OS_ANDROID)
84
85// Implement string hash functions so that strings of various flavors can
86// be used as keys in STL maps and sets.  The hash algorithm comes from the
87// GNU C++ library, in <tr1/functional>.  It is duplicated here because GCC
88// versions prior to 4.3.2 are unable to compile <tr1/functional> when RTTI
89// is disabled, as it is in our build.
90
91#define DEFINE_STRING_HASH(string_type) \
92    template<> \
93    struct hash<string_type> { \
94      std::size_t operator()(const string_type& s) const { \
95        std::size_t result = 0; \
96        for (string_type::const_iterator i = s.begin(); i != s.end(); ++i) \
97          result = (result * 131) + *i; \
98        return result; \
99      } \
100    }
101
102DEFINE_STRING_HASH(std::string);
103DEFINE_STRING_HASH(string16);
104
105#undef DEFINE_STRING_HASH
106
107}  // namespace BASE_HASH_NAMESPACE
108
109#else  // COMPILER
110#error define BASE_HASH_NAMESPACE for your compiler
111#endif  // COMPILER
112
113namespace base {
114using BASE_HASH_NAMESPACE::hash_map;
115using BASE_HASH_NAMESPACE::hash_multimap;
116using BASE_HASH_NAMESPACE::hash_multiset;
117using BASE_HASH_NAMESPACE::hash_set;
118}
119
120#endif  // BASE_CONTAINERS_HASH_TABLES_H_
121