cc/hash_pair.h

   1 // Copyright (c) 2012 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 // Defines methods for hashing a pair of integers.
   6
   7 #ifndef CC_HASH_PAIR_H_
   8 #define CC_HASH_PAIR_H_
   9
  10 #include "base/hash_tables.h"
  11
  12 #if defined(COMPILER_MSVC)
  13
  14 #define DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) \
  15     template<> \
  16     inline std::size_t hash_value<std::pair<type1, type2> >( \
  17         const std::pair<type1, type2>& value)
  18
  19 #define DEFINE_PAIR_HASH_FUNCTION_END()
  20
  21 #elif defined(COMPILER_GCC)
  22
  23 #define DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) \
  24     template<> \
  25     struct hash<std::pair<type1, type2> > { \
  26       std::size_t operator()(std::pair<type1, type2> value) const
  27
  28 #define DEFINE_PAIR_HASH_FUNCTION_END() \
  29     };
  30
  31 #else
  32 #error define DEFINE_PAIR_HASH_FUNCTION_START for your compiler
  33 #endif // COMPILER
  34
  35 namespace BASE_HASH_NAMESPACE {
  36
  37 // Implement hashing for pairs of at-most 32 bit integer values.
  38 // When size_t is 32 bits, we turn the 64-bit hash code into 32 bits by using
  39 // multiply-add hashing. This algorithm, as described in
  40 // Theorem 4.3.3 of the thesis "Über die Komplexität der Multiplikation in
  41 // eingeschränkten Branchingprogrammmodellen" by Woelfel, is:
  42 //
  43 //   h32(x32, y32) = (h64(x32, y32) * randOdd64 + rand16 * 2^16) % 2^64 / 2^32
  44
  45 #define DEFINE_32BIT_PAIR_HASH(type1, type2) \
  46     DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) { \
  47       uint64 first = value.first; \
  48       uint32 second = value.second; \
  49       uint64 hash64 = (first << 32) | second; \
  50       \
  51       if (sizeof(std::size_t) >= sizeof(uint64)) \
  52         return static_cast<std::size_t>(hash64); \
  53       \
  54       uint64 oddRandom = 481046412LL << 32 | 1025306954LL; \
  55       uint32 shiftRandom = 10121U << 16; \
  56       \
  57       hash64 = hash64 * oddRandom + shiftRandom; \
  58       std::size_t highBits = static_cast<std::size_t>( \
  59           hash64 >> (sizeof(uint64) - sizeof(std::size_t))); \
  60       return highBits; \
  61     } \
  62   DEFINE_PAIR_HASH_FUNCTION_END();
  63
  64 DEFINE_32BIT_PAIR_HASH(short, short);
  65 DEFINE_32BIT_PAIR_HASH(short, unsigned short);
  66 DEFINE_32BIT_PAIR_HASH(short, int);
  67 DEFINE_32BIT_PAIR_HASH(short, unsigned);
  68 DEFINE_32BIT_PAIR_HASH(unsigned short, short);
  69 DEFINE_32BIT_PAIR_HASH(unsigned short, unsigned short);
  70 DEFINE_32BIT_PAIR_HASH(unsigned short, int);
  71 DEFINE_32BIT_PAIR_HASH(unsigned short, unsigned);
  72 DEFINE_32BIT_PAIR_HASH(int, short);
  73 DEFINE_32BIT_PAIR_HASH(int, unsigned short);
  74 DEFINE_32BIT_PAIR_HASH(int, int);
  75 DEFINE_32BIT_PAIR_HASH(int, unsigned);
  76 DEFINE_32BIT_PAIR_HASH(unsigned, short);
  77 DEFINE_32BIT_PAIR_HASH(unsigned, unsigned short);
  78 DEFINE_32BIT_PAIR_HASH(unsigned, int);
  79 DEFINE_32BIT_PAIR_HASH(unsigned, unsigned);
  80
  81 #undef DEFINE_32BIT_PAIR_HASH
  82
  83 // Implement hashing for pairs of up-to 64-bit integer values.
  84 // We use the compound integer hash method to produce a 64-bit hash code, by
  85 // breaking the two 64-bit inputs into 4 32-bit values:
  86 // http://opendatastructures.org/versions/edition-0.1d/ods-java/node33.html#SECTION00832000000000000000
  87 // Then we reduce our result to 32 bits if required, similar to above.
  88
  89 #define DEFINE_64BIT_PAIR_HASH(type1, type2) \
  90     DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) { \
  91       uint32 shortRandom1 = 842304669U; \
  92       uint32 shortRandom2 = 619063811U; \
  93       uint32 shortRandom3 = 937041849U; \
  94       uint32 shortRandom4 = 3309708029U; \
  95       \
  96       uint64 value1 = value.first; \
  97       uint64 value2 = value.second; \
  98       uint32 value1a = static_cast<uint32>(value1 & 0xffffffff); \
  99       uint32 value1b = static_cast<uint32>((value1 >> 32) & 0xffffffff); \
 100       uint32 value2a = static_cast<uint32>(value2 & 0xffffffff); \
 101       uint32 value2b = static_cast<uint32>((value2 >> 32) & 0xffffffff); \
 102       \
 103       uint64 product1 = static_cast<uint64>(value1a) * shortRandom1; \
 104       uint64 product2 = static_cast<uint64>(value1b) * shortRandom2; \
 105       uint64 product3 = static_cast<uint64>(value2a) * shortRandom3; \
 106       uint64 product4 = static_cast<uint64>(value2b) * shortRandom4; \
 107       \
 108       uint64 hash64 = product1 + product2 + product3 + product4; \
 109       \
 110       if (sizeof(std::size_t) >= sizeof(uint64)) \
 111         return static_cast<std::size_t>(hash64); \
 112       \
 113       uint64 oddRandom = 1578233944LL << 32 | 194370989LL; \
 114       uint32 shiftRandom = 20591U << 16; \
 115       \
 116       hash64 = hash64 * oddRandom + shiftRandom; \
 117       std::size_t highBits = static_cast<std::size_t>( \
 118           hash64 >> (sizeof(uint64) - sizeof(std::size_t))); \
 119       return highBits; \
 120     } \
 121   DEFINE_PAIR_HASH_FUNCTION_END();
 122
 123 DEFINE_64BIT_PAIR_HASH(short, int64);
 124 DEFINE_64BIT_PAIR_HASH(short, uint64);
 125 DEFINE_64BIT_PAIR_HASH(unsigned short, int64);
 126 DEFINE_64BIT_PAIR_HASH(unsigned short, uint64);
 127 DEFINE_64BIT_PAIR_HASH(int, int64);
 128 DEFINE_64BIT_PAIR_HASH(int, uint64);
 129 DEFINE_64BIT_PAIR_HASH(unsigned, int64);
 130 DEFINE_64BIT_PAIR_HASH(unsigned, uint64);
 131 DEFINE_64BIT_PAIR_HASH(int64, short);
 132 DEFINE_64BIT_PAIR_HASH(int64, unsigned short);
 133 DEFINE_64BIT_PAIR_HASH(int64, int);
 134 DEFINE_64BIT_PAIR_HASH(int64, unsigned);
 135 DEFINE_64BIT_PAIR_HASH(int64, int64);
 136 DEFINE_64BIT_PAIR_HASH(int64, uint64);
 137 DEFINE_64BIT_PAIR_HASH(uint64, short);
 138 DEFINE_64BIT_PAIR_HASH(uint64, unsigned short);
 139 DEFINE_64BIT_PAIR_HASH(uint64, int);
 140 DEFINE_64BIT_PAIR_HASH(uint64, unsigned);
 141 DEFINE_64BIT_PAIR_HASH(uint64, int64);
 142 DEFINE_64BIT_PAIR_HASH(uint64, uint64);
 143
 144 #undef DEFINE_64BIT_PAIR_HASH
 145 }
 146
 147 #undef DEFINE_PAIR_HASH_FUNCTION_START
 148 #undef DEFINE_PAIR_HASH_FUNCTION_END
 149
 150 #endif  // CC_HASH_PAIR_H_