base/hash_tables.h

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