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 // Copyright (c) 2011 The Chromium Authors. All rights reserved.

 // Use of this source code is governed by a BSD-style license that can be

 // found in the LICENSE file.

 //

 //

 // Deal with the differences between Microsoft and GNU implemenations

 // of hash_map. Allows all platforms to use |base::hash_map| and

 // |base::hash_set|.

 //  eg:

 //   base::hash_map<int> my_map;

 //   base::hash_set<int> my_set;

 //

 // NOTE: It is an explicit non-goal of this class to provide a generic hash

 // function for pointers.  If you want to hash a pointers to a particular class,

 // please define the template specialization elsewhere (for example, in its

 // header file) and keep it specific to just pointers to that class.  This is

 // because identity hashes are not desirable for all types that might show up

 // in containers as pointers.

 #ifndef BASE_CONTAINERS_HASH_TABLES_H_

 #define BASE_CONTAINERS_HASH_TABLES_H_

 #include <utility>

 #include "base/basictypes.h"

 #include "base/strings/string16.h"

 #include "build/build_config.h"

 #if defined(COMPILER_MSVC)

 #include <hash_map>

 #include <hash_set>

 #define BASE_HASH_NAMESPACE stdext

 #elif defined(COMPILER_GCC)

 #if defined(OS_ANDROID)

 #define BASE_HASH_NAMESPACE std

 #else

 #define BASE_HASH_NAMESPACE __gnu_cxx

 #endif

 // This is a hack to disable the gcc 4.4 warning about hash_map and hash_set

 // being deprecated.  We can get rid of this when we upgrade to VS2008 and we

 // can use <tr1/unordered_map> and <tr1/unordered_set>.

 #ifdef __DEPRECATED

 #define CHROME_OLD__DEPRECATED __DEPRECATED

 #undef __DEPRECATED

 #endif

 #if defined(OS_ANDROID)

 #include <hash_map>

 #include <hash_set>

 #else

 #include <ext/hash_map>

 #include <ext/hash_set>

 #endif

 #include <string>

 #ifdef CHROME_OLD__DEPRECATED

 #define __DEPRECATED CHROME_OLD__DEPRECATED

 #undef CHROME_OLD__DEPRECATED

 #endif

 namespace BASE_HASH_NAMESPACE {

 #if !defined(OS_ANDROID)

 // The GNU C++ library provides identity hash functions for many integral types,

 // but not for |long long|.  This hash function will truncate if |size_t| is

 // narrower than |long long|.  This is probably good enough for what we will

 // use it for.

 #define DEFINE_TRIVIAL_HASH(integral_type) \

     template<> \

     struct hash<integral_type> { \

       std::size_t operator()(integral_type value) const { \

         return static_cast<std::size_t>(value); \

       } \

     }

 DEFINE_TRIVIAL_HASH(long long);

 DEFINE_TRIVIAL_HASH(unsigned long long);

 #undef DEFINE_TRIVIAL_HASH

 #endif  // !defined(OS_ANDROID)

 // Implement string hash functions so that strings of various flavors can

 // be used as keys in STL maps and sets.  The hash algorithm comes from the

 // GNU C++ library, in <tr1/functional>.  It is duplicated here because GCC

 // versions prior to 4.3.2 are unable to compile <tr1/functional> when RTTI

 // is disabled, as it is in our build.

 #define DEFINE_STRING_HASH(string_type) \

     template<> \

     struct hash<string_type> { \

       std::size_t operator()(const string_type& s) const { \

         std::size_t result = 0; \

         for (string_type::const_iterator i = s.begin(); i != s.end(); ++i) \

           result = (result * 131) + *i; \

         return result; \

       } \

     }

 DEFINE_STRING_HASH(std::string);

 DEFINE_STRING_HASH(string16);

 #undef DEFINE_STRING_HASH

 }  // namespace BASE_HASH_NAMESPACE

 #else  // COMPILER

 #error define BASE_HASH_NAMESPACE for your compiler

 #endif  // COMPILER

 namespace base {

 using BASE_HASH_NAMESPACE::hash_map;

 using BASE_HASH_NAMESPACE::hash_multimap;

 using BASE_HASH_NAMESPACE::hash_multiset;

 using BASE_HASH_NAMESPACE::hash_set;

 // Implement hashing for pairs of at-most 32 bit integer values.

 // When size_t is 32 bits, we turn the 64-bit hash code into 32 bits by using

 // multiply-add hashing. This algorithm, as described in

 // Theorem 4.3.3 of the thesis "Über die Komplexität der Multiplikation in

 // eingeschränkten Branchingprogrammmodellen" by Woelfel, is:

 //

 //   h32(x32, y32) = (h64(x32, y32) * rand_odd64 + rand16 * 2^16) % 2^64 / 2^32

 //

 // Contact danakj@chromium.org for any questions.

 inline std::size_t HashInts32(uint32 value1, uint32 value2) {

   uint64 value1_64 = value1;

   uint64 hash64 = (value1_64 << 32) | value2;

   if (sizeof(std::size_t) >= sizeof(uint64))

     return static_cast<std::size_t>(hash64);

   uint64 odd_random = 481046412LL << 32 | 1025306955LL;

   uint32 shift_random = 10121U << 16;

   hash64 = hash64 * odd_random + shift_random;

   std::size_t high_bits = static_cast<std::size_t>(

       hash64 >> (sizeof(uint64) - sizeof(std::size_t)));

   return high_bits;

 }

 // Implement hashing for pairs of up-to 64-bit integer values.

 // We use the compound integer hash method to produce a 64-bit hash code, by

 // breaking the two 64-bit inputs into 4 32-bit values:

 // http://opendatastructures.org/versions/edition-0.1d/ods-java/node33.html#SECTION00832000000000000000

 // Then we reduce our result to 32 bits if required, similar to above.

 inline std::size_t HashInts64(uint64 value1, uint64 value2) {

   uint32 short_random1 = 842304669U;

   uint32 short_random2 = 619063811U;

   uint32 short_random3 = 937041849U;

   uint32 short_random4 = 3309708029U;

   uint32 value1a = static_cast<uint32>(value1 & 0xffffffff);

   uint32 value1b = static_cast<uint32>((value1 >> 32) & 0xffffffff);

   uint32 value2a = static_cast<uint32>(value2 & 0xffffffff);

   uint32 value2b = static_cast<uint32>((value2 >> 32) & 0xffffffff);

   uint64 product1 = static_cast<uint64>(value1a) * short_random1;

   uint64 product2 = static_cast<uint64>(value1b) * short_random2;

   uint64 product3 = static_cast<uint64>(value2a) * short_random3;

   uint64 product4 = static_cast<uint64>(value2b) * short_random4;

   uint64 hash64 = product1 + product2 + product3 + product4;

   if (sizeof(std::size_t) >= sizeof(uint64))

     return static_cast<std::size_t>(hash64);

   uint64 odd_random = 1578233944LL << 32 | 194370989LL;

   uint32 shift_random = 20591U << 16;

   hash64 = hash64 * odd_random + shift_random;

   std::size_t high_bits = static_cast<std::size_t>(

       hash64 >> (sizeof(uint64) - sizeof(std::size_t)));

   return high_bits;

 }

 #define DEFINE_32BIT_PAIR_HASH(Type1, Type2) \

 inline std::size_t HashPair(Type1 value1, Type2 value2) { \

   return HashInts32(value1, value2); \

 }

 DEFINE_32BIT_PAIR_HASH(int16, int16);

 DEFINE_32BIT_PAIR_HASH(int16, uint16);

 DEFINE_32BIT_PAIR_HASH(int16, int32);

 DEFINE_32BIT_PAIR_HASH(int16, uint32);

 DEFINE_32BIT_PAIR_HASH(uint16, int16);

 DEFINE_32BIT_PAIR_HASH(uint16, uint16);

 DEFINE_32BIT_PAIR_HASH(uint16, int32);

 DEFINE_32BIT_PAIR_HASH(uint16, uint32);

 DEFINE_32BIT_PAIR_HASH(int32, int16);

 DEFINE_32BIT_PAIR_HASH(int32, uint16);

 DEFINE_32BIT_PAIR_HASH(int32, int32);

 DEFINE_32BIT_PAIR_HASH(int32, uint32);

 DEFINE_32BIT_PAIR_HASH(uint32, int16);

 DEFINE_32BIT_PAIR_HASH(uint32, uint16);

 DEFINE_32BIT_PAIR_HASH(uint32, int32);

 DEFINE_32BIT_PAIR_HASH(uint32, uint32);

 #undef DEFINE_32BIT_PAIR_HASH

 #define DEFINE_64BIT_PAIR_HASH(Type1, Type2) \

 inline std::size_t HashPair(Type1 value1, Type2 value2) { \

   return HashInts64(value1, value2); \

 }

 DEFINE_64BIT_PAIR_HASH(int16, int64);

 DEFINE_64BIT_PAIR_HASH(int16, uint64);

 DEFINE_64BIT_PAIR_HASH(uint16, int64);

 DEFINE_64BIT_PAIR_HASH(uint16, uint64);

 DEFINE_64BIT_PAIR_HASH(int32, int64);

 DEFINE_64BIT_PAIR_HASH(int32, uint64);

 DEFINE_64BIT_PAIR_HASH(uint32, int64);

 DEFINE_64BIT_PAIR_HASH(uint32, uint64);

 DEFINE_64BIT_PAIR_HASH(int64, int16);

 DEFINE_64BIT_PAIR_HASH(int64, uint16);

 DEFINE_64BIT_PAIR_HASH(int64, int32);

 DEFINE_64BIT_PAIR_HASH(int64, uint32);

 DEFINE_64BIT_PAIR_HASH(int64, int64);

 DEFINE_64BIT_PAIR_HASH(int64, uint64);

 DEFINE_64BIT_PAIR_HASH(uint64, int16);

 DEFINE_64BIT_PAIR_HASH(uint64, uint16);

 DEFINE_64BIT_PAIR_HASH(uint64, int32);

 DEFINE_64BIT_PAIR_HASH(uint64, uint32);

 DEFINE_64BIT_PAIR_HASH(uint64, int64);

 DEFINE_64BIT_PAIR_HASH(uint64, uint64);

 #undef DEFINE_64BIT_PAIR_HASH

 }  // namespace base

 namespace BASE_HASH_NAMESPACE {

 // Implement methods for hashing a pair of integers, so they can be used as

 // keys in STL containers.

 #if defined(COMPILER_MSVC)

 template<typename Type1, typename Type2>

 inline std::size_t hash_value(const std::pair<Type1, Type2>& value) {

   return base::HashPair(value.first, value.second);

 }

 #elif defined(COMPILER_GCC)

 template<typename Type1, typename Type2>

 struct hash<std::pair<Type1, Type2> > {

   std::size_t operator()(std::pair<Type1, Type2> value) const {

     return base::HashPair(value.first, value.second);

   }

 };

 #else

 #error define hash<std::pair<Type1, Type2> > for your compiler

 #endif  // COMPILER

 }

 #undef DEFINE_PAIR_HASH_FUNCTION_START

 #undef DEFINE_PAIR_HASH_FUNCTION_END

 #endif  // BASE_CONTAINERS_HASH_TABLES_H_