base/hash_tables.h

   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>
  32 namespace base {
  33 using stdext::hash_map;
  34 using 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
  54 namespace base {
  55 using __gnu_cxx::hash_map;
  56 using __gnu_cxx::hash_set;
  57 }  // namespace base
  58
  59 namespace __gnu_cxx {
  60
  61 // The GNU C++ library provides identiy hash functions for many integral types,
  62 // but not for |long long|.  This hash function will truncate if |size_t| is
  63 // narrower than |long long|.  This is probably good enough for what we will
  64 // use it for.
  65
  66 #define DEFINE_TRIVIAL_HASH(integral_type) \
  67     template<> \
  68     struct hash<integral_type> { \
  69       std::size_t operator()(integral_type value) const { \
  70         return static_cast<std::size_t>(value); \
  71       } \
  72     }
  73
  74 DEFINE_TRIVIAL_HASH(long long);
  75 DEFINE_TRIVIAL_HASH(unsigned long long);
  76
  77 #undef DEFINE_TRIVIAL_HASH
  78
  79 // Implement string hash functions so that strings of various flavors can
  80 // be used as keys in STL maps and sets.  The hash algorithm comes from the
  81 // GNU C++ library, in <tr1/functional>.  It is duplicated here because GCC
  82 // versions prior to 4.3.2 are unable to compile <tr1/functional> when RTTI
  83 // is disabled, as it is in our build.
  84
  85 #define DEFINE_STRING_HASH(string_type) \
  86     template<> \
  87     struct hash<string_type> { \
  88       std::size_t operator()(const string_type& s) const { \
  89         std::size_t result = 0; \
  90         for (string_type::const_iterator i = s.begin(); i != s.end(); ++i) \
  91           result = (result * 131) + *i; \
  92         return result; \
  93       } \
  94     }
  95
  96 DEFINE_STRING_HASH(std::string);
  97 DEFINE_STRING_HASH(std::wstring);
  98
  99 #if defined(WCHAR_T_IS_UTF32)
 100 // If string16 and std::wstring are not the same type, provide a
 101 // specialization for string16.
 102 DEFINE_STRING_HASH(string16);
 103 #endif  // WCHAR_T_IS_UTF32
 104
 105 #undef DEFINE_STRING_HASH
 106
 107 }  // namespace __gnu_cxx
 108
 109 #endif  // COMPILER
 110
 111 #endif  // BASE_HASH_TABLES_H_