text: // 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 methods for hashing a pair of integers, so they can be used as
  // keys in STL containers.
  
  #if defined(COMPILER_MSVC)
  
  #define DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) \
      template<> \
      inline std::size_t hash_value<std::pair<type1, type2> >( \
          const std::pair<type1, type2>& value)
  
  #define DEFINE_PAIR_HASH_FUNCTION_END()
  
  #elif defined(COMPILER_GCC)
  
  #define DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) \
      template<> \
      struct hash<std::pair<type1, type2> > { \
        std::size_t operator()(std::pair<type1, type2> value) const
  
  #define DEFINE_PAIR_HASH_FUNCTION_END() \
      };
  
  #else
  #error define DEFINE_PAIR_HASH_FUNCTION_START for your compiler
  #endif  // COMPILER
  
  namespace BASE_HASH_NAMESPACE {
  
  // 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.
  #define DEFINE_32BIT_PAIR_HASH(type1, type2) \
      DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) { \
        uint64 first = value.first; \
        uint32 second = value.second; \
        uint64 hash64 = (first << 32) | second; \
        \
        if (sizeof(std::size_t) >= sizeof(uint64)) \
          return static_cast<std::size_t>(hash64); \
        \
        uint64 odd_random = 481046412LL << 32 | 1025306954LL; \
        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; \
      } \
    DEFINE_PAIR_HASH_FUNCTION_END();
  
  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
  
  // 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.
  #define DEFINE_64BIT_PAIR_HASH(type1, type2) \
      DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) { \
        uint32 short_random1 = 842304669U; \
        uint32 short_random2 = 619063811U; \
        uint32 short_random3 = 937041849U; \
        uint32 short_random4 = 3309708029U; \
        \
        uint64 value1 = value.first; \
        uint64 value2 = value.second; \
        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_PAIR_HASH_FUNCTION_END();
  
  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
  }
  
  #undef DEFINE_PAIR_HASH_FUNCTION_START
  #undef DEFINE_PAIR_HASH_FUNCTION_END
  
  #endif  // BASE_CONTAINERS_HASH_TABLES_H_
  