hash_tables.h revision d67849366c6c6af8aa96afd9503cdd028afd2db1 
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#ifndef ANDROID
62// Already defined for android
63
64// The GNU C++ library provides identity hash functions for many integral types,
65// but not for |long long|.  This hash function will truncate if |size_t| is
66// narrower than |long long|.  This is probably good enough for what we will
67// use it for.
68
69#define DEFINE_TRIVIAL_HASH(integral_type) \
70    template<> \
71    struct hash<integral_type> { \
72      std::size_t operator()(integral_type value) const { \
73        return static_cast<std::size_t>(value); \
74      } \
75    }
76
77DEFINE_TRIVIAL_HASH(long long);
78DEFINE_TRIVIAL_HASH(unsigned long long);
79
80#undef DEFINE_TRIVIAL_HASH
81#endif
82
83// Implement string hash functions so that strings of various flavors can
84// be used as keys in STL maps and sets.  The hash algorithm comes from the
85// GNU C++ library, in <tr1/functional>.  It is duplicated here because GCC
86// versions prior to 4.3.2 are unable to compile <tr1/functional> when RTTI
87// is disabled, as it is in our build.
88
89#define DEFINE_STRING_HASH(string_type) \
90    template<> \
91    struct hash<string_type> { \
92      std::size_t operator()(const string_type& s) const { \
93        std::size_t result = 0; \
94        for (string_type::const_iterator i = s.begin(); i != s.end(); ++i) \
95          result = (result * 131) + *i; \
96        return result; \
97      } \
98    }
99
100DEFINE_STRING_HASH(std::string);
101DEFINE_STRING_HASH(std::wstring);
102
103#if defined(WCHAR_T_IS_UTF32)
104// If string16 and std::wstring are not the same type, provide a
105// specialization for string16.
106DEFINE_STRING_HASH(string16);
107#endif  // WCHAR_T_IS_UTF32
108
109#undef DEFINE_STRING_HASH
110
111}  // namespace __gnu_cxx
112
113#endif  // COMPILER
114
115#endif  // BASE_HASH_TABLES_H_
116