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      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 <utility>
     25 
     26 #include "base/basictypes.h"
     27 #include "base/strings/string16.h"
     28 #include "build/build_config.h"
     29 
     30 #if defined(COMPILER_MSVC)
     31 #include <hash_map>
     32 #include <hash_set>
     33 
     34 #define BASE_HASH_NAMESPACE stdext
     35 
     36 #elif defined(COMPILER_GCC)
     37 #if defined(OS_ANDROID)
     38 #define BASE_HASH_NAMESPACE std
     39 #else
     40 #define BASE_HASH_NAMESPACE __gnu_cxx
     41 #endif
     42 
     43 // This is a hack to disable the gcc 4.4 warning about hash_map and hash_set
     44 // being deprecated.  We can get rid of this when we upgrade to VS2008 and we
     45 // can use <tr1/unordered_map> and <tr1/unordered_set>.
     46 #ifdef __DEPRECATED
     47 #define CHROME_OLD__DEPRECATED __DEPRECATED
     48 #undef __DEPRECATED
     49 #endif
     50 
     51 #if defined(OS_ANDROID)
     52 #include <hash_map>
     53 #include <hash_set>
     54 #else
     55 #include <ext/hash_map>
     56 #include <ext/hash_set>
     57 #endif
     58 
     59 #include <string>
     60 
     61 #ifdef CHROME_OLD__DEPRECATED
     62 #define __DEPRECATED CHROME_OLD__DEPRECATED
     63 #undef CHROME_OLD__DEPRECATED
     64 #endif
     65 
     66 namespace BASE_HASH_NAMESPACE {
     67 
     68 #if !defined(OS_ANDROID)
     69 // The GNU C++ library provides identity hash functions for many integral types,
     70 // but not for |long long|.  This hash function will truncate if |size_t| is
     71 // narrower than |long long|.  This is probably good enough for what we will
     72 // use it for.
     73 
     74 #define DEFINE_TRIVIAL_HASH(integral_type) \
     75     template<> \
     76     struct hash<integral_type> { \
     77       std::size_t operator()(integral_type value) const { \
     78         return static_cast<std::size_t>(value); \
     79       } \
     80     }
     81 
     82 DEFINE_TRIVIAL_HASH(long long);
     83 DEFINE_TRIVIAL_HASH(unsigned long long);
     84 
     85 #undef DEFINE_TRIVIAL_HASH
     86 #endif  // !defined(OS_ANDROID)
     87 
     88 // Implement string hash functions so that strings of various flavors can
     89 // be used as keys in STL maps and sets.  The hash algorithm comes from the
     90 // GNU C++ library, in <tr1/functional>.  It is duplicated here because GCC
     91 // versions prior to 4.3.2 are unable to compile <tr1/functional> when RTTI
     92 // is disabled, as it is in our build.
     93 
     94 #define DEFINE_STRING_HASH(string_type) \
     95     template<> \
     96     struct hash<string_type> { \
     97       std::size_t operator()(const string_type& s) const { \
     98         std::size_t result = 0; \
     99         for (string_type::const_iterator i = s.begin(); i != s.end(); ++i) \
    100           result = (result * 131) + *i; \
    101         return result; \
    102       } \
    103     }
    104 
    105 DEFINE_STRING_HASH(std::string);
    106 DEFINE_STRING_HASH(base::string16);
    107 
    108 #undef DEFINE_STRING_HASH
    109 
    110 }  // namespace BASE_HASH_NAMESPACE
    111 
    112 #else  // COMPILER
    113 #error define BASE_HASH_NAMESPACE for your compiler
    114 #endif  // COMPILER
    115 
    116 namespace base {
    117 using BASE_HASH_NAMESPACE::hash_map;
    118 using BASE_HASH_NAMESPACE::hash_multimap;
    119 using BASE_HASH_NAMESPACE::hash_multiset;
    120 using BASE_HASH_NAMESPACE::hash_set;
    121 
    122 // Implement hashing for pairs of at-most 32 bit integer values.
    123 // When size_t is 32 bits, we turn the 64-bit hash code into 32 bits by using
    124 // multiply-add hashing. This algorithm, as described in
    125 // Theorem 4.3.3 of the thesis "ber die Komplexitt der Multiplikation in
    126 // eingeschrnkten Branchingprogrammmodellen" by Woelfel, is:
    127 //
    128 //   h32(x32, y32) = (h64(x32, y32) * rand_odd64 + rand16 * 2^16) % 2^64 / 2^32
    129 //
    130 // Contact danakj (at) chromium.org for any questions.
    131 inline std::size_t HashInts32(uint32 value1, uint32 value2) {
    132   uint64 value1_64 = value1;
    133   uint64 hash64 = (value1_64 << 32) | value2;
    134 
    135   if (sizeof(std::size_t) >= sizeof(uint64))
    136     return static_cast<std::size_t>(hash64);
    137 
    138   uint64 odd_random = 481046412LL << 32 | 1025306955LL;
    139   uint32 shift_random = 10121U << 16;
    140 
    141   hash64 = hash64 * odd_random + shift_random;
    142   std::size_t high_bits = static_cast<std::size_t>(
    143       hash64 >> (8 * (sizeof(uint64) - sizeof(std::size_t))));
    144   return high_bits;
    145 }
    146 
    147 // Implement hashing for pairs of up-to 64-bit integer values.
    148 // We use the compound integer hash method to produce a 64-bit hash code, by
    149 // breaking the two 64-bit inputs into 4 32-bit values:
    150 // http://opendatastructures.org/versions/edition-0.1d/ods-java/node33.html#SECTION00832000000000000000
    151 // Then we reduce our result to 32 bits if required, similar to above.
    152 inline std::size_t HashInts64(uint64 value1, uint64 value2) {
    153   uint32 short_random1 = 842304669U;
    154   uint32 short_random2 = 619063811U;
    155   uint32 short_random3 = 937041849U;
    156   uint32 short_random4 = 3309708029U;
    157 
    158   uint32 value1a = static_cast<uint32>(value1 & 0xffffffff);
    159   uint32 value1b = static_cast<uint32>((value1 >> 32) & 0xffffffff);
    160   uint32 value2a = static_cast<uint32>(value2 & 0xffffffff);
    161   uint32 value2b = static_cast<uint32>((value2 >> 32) & 0xffffffff);
    162 
    163   uint64 product1 = static_cast<uint64>(value1a) * short_random1;
    164   uint64 product2 = static_cast<uint64>(value1b) * short_random2;
    165   uint64 product3 = static_cast<uint64>(value2a) * short_random3;
    166   uint64 product4 = static_cast<uint64>(value2b) * short_random4;
    167 
    168   uint64 hash64 = product1 + product2 + product3 + product4;
    169 
    170   if (sizeof(std::size_t) >= sizeof(uint64))
    171     return static_cast<std::size_t>(hash64);
    172 
    173   uint64 odd_random = 1578233944LL << 32 | 194370989LL;
    174   uint32 shift_random = 20591U << 16;
    175 
    176   hash64 = hash64 * odd_random + shift_random;
    177   std::size_t high_bits = static_cast<std::size_t>(
    178       hash64 >> (8 * (sizeof(uint64) - sizeof(std::size_t))));
    179   return high_bits;
    180 }
    181 
    182 #define DEFINE_32BIT_PAIR_HASH(Type1, Type2) \
    183 inline std::size_t HashPair(Type1 value1, Type2 value2) { \
    184   return HashInts32(value1, value2); \
    185 }
    186 
    187 DEFINE_32BIT_PAIR_HASH(int16, int16);
    188 DEFINE_32BIT_PAIR_HASH(int16, uint16);
    189 DEFINE_32BIT_PAIR_HASH(int16, int32);
    190 DEFINE_32BIT_PAIR_HASH(int16, uint32);
    191 DEFINE_32BIT_PAIR_HASH(uint16, int16);
    192 DEFINE_32BIT_PAIR_HASH(uint16, uint16);
    193 DEFINE_32BIT_PAIR_HASH(uint16, int32);
    194 DEFINE_32BIT_PAIR_HASH(uint16, uint32);
    195 DEFINE_32BIT_PAIR_HASH(int32, int16);
    196 DEFINE_32BIT_PAIR_HASH(int32, uint16);
    197 DEFINE_32BIT_PAIR_HASH(int32, int32);
    198 DEFINE_32BIT_PAIR_HASH(int32, uint32);
    199 DEFINE_32BIT_PAIR_HASH(uint32, int16);
    200 DEFINE_32BIT_PAIR_HASH(uint32, uint16);
    201 DEFINE_32BIT_PAIR_HASH(uint32, int32);
    202 DEFINE_32BIT_PAIR_HASH(uint32, uint32);
    203 
    204 #undef DEFINE_32BIT_PAIR_HASH
    205 
    206 #define DEFINE_64BIT_PAIR_HASH(Type1, Type2) \
    207 inline std::size_t HashPair(Type1 value1, Type2 value2) { \
    208   return HashInts64(value1, value2); \
    209 }
    210 
    211 DEFINE_64BIT_PAIR_HASH(int16, int64);
    212 DEFINE_64BIT_PAIR_HASH(int16, uint64);
    213 DEFINE_64BIT_PAIR_HASH(uint16, int64);
    214 DEFINE_64BIT_PAIR_HASH(uint16, uint64);
    215 DEFINE_64BIT_PAIR_HASH(int32, int64);
    216 DEFINE_64BIT_PAIR_HASH(int32, uint64);
    217 DEFINE_64BIT_PAIR_HASH(uint32, int64);
    218 DEFINE_64BIT_PAIR_HASH(uint32, uint64);
    219 DEFINE_64BIT_PAIR_HASH(int64, int16);
    220 DEFINE_64BIT_PAIR_HASH(int64, uint16);
    221 DEFINE_64BIT_PAIR_HASH(int64, int32);
    222 DEFINE_64BIT_PAIR_HASH(int64, uint32);
    223 DEFINE_64BIT_PAIR_HASH(int64, int64);
    224 DEFINE_64BIT_PAIR_HASH(int64, uint64);
    225 DEFINE_64BIT_PAIR_HASH(uint64, int16);
    226 DEFINE_64BIT_PAIR_HASH(uint64, uint16);
    227 DEFINE_64BIT_PAIR_HASH(uint64, int32);
    228 DEFINE_64BIT_PAIR_HASH(uint64, uint32);
    229 DEFINE_64BIT_PAIR_HASH(uint64, int64);
    230 DEFINE_64BIT_PAIR_HASH(uint64, uint64);
    231 
    232 #undef DEFINE_64BIT_PAIR_HASH
    233 }  // namespace base
    234 
    235 namespace BASE_HASH_NAMESPACE {
    236 
    237 // Implement methods for hashing a pair of integers, so they can be used as
    238 // keys in STL containers.
    239 
    240 #if defined(COMPILER_MSVC)
    241 
    242 template<typename Type1, typename Type2>
    243 inline std::size_t hash_value(const std::pair<Type1, Type2>& value) {
    244   return base::HashPair(value.first, value.second);
    245 }
    246 
    247 #elif defined(COMPILER_GCC)
    248 template<typename Type1, typename Type2>
    249 struct hash<std::pair<Type1, Type2> > {
    250   std::size_t operator()(std::pair<Type1, Type2> value) const {
    251     return base::HashPair(value.first, value.second);
    252   }
    253 };
    254 
    255 #else
    256 #error define hash<std::pair<Type1, Type2> > for your compiler
    257 #endif  // COMPILER
    258 
    259 }
    260 
    261 #undef DEFINE_PAIR_HASH_FUNCTION_START
    262 #undef DEFINE_PAIR_HASH_FUNCTION_END
    263 
    264 #endif  // BASE_CONTAINERS_HASH_TABLES_H_
    265