cc/base/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_BASE_HASH_PAIR_H_
   8 #define CC_BASE_HASH_PAIR_H_
   9
  10 #include <utility>
  11
  12 #include "base/basictypes.h"
  13 #include "base/hash_tables.h"
  14
  15 #if defined(COMPILER_MSVC)
  16
  17 #define DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) \
  18     template<> \
  19     inline std::size_t hash_value<std::pair<type1, type2> >( \
  20         const std::pair<type1, type2>& value)
  21
  22 #define DEFINE_PAIR_HASH_FUNCTION_END()
  23
  24 #elif defined(COMPILER_GCC)
  25
  26 #define DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) \
  27     template<> \
  28     struct hash<std::pair<type1, type2> > { \
  29       std::size_t operator()(std::pair<type1, type2> value) const
  30
  31 #define DEFINE_PAIR_HASH_FUNCTION_END() \
  32     };
  33
  34 #else
  35 #error define DEFINE_PAIR_HASH_FUNCTION_START for your compiler
  36 #endif  // COMPILER
  37
  38 namespace BASE_HASH_NAMESPACE {
  39
  40 // Implement hashing for pairs of at-most 32 bit integer values.
  41 // When size_t is 32 bits, we turn the 64-bit hash code into 32 bits by using
  42 // multiply-add hashing. This algorithm, as described in
  43 // Theorem 4.3.3 of the thesis "Über die Komplexität der Multiplikation in
  44 // eingeschränkten Branchingprogrammmodellen" by Woelfel, is:
  45 //
  46 //   h32(x32, y32) = (h64(x32, y32) * rand_odd64 + rand16 * 2^16) % 2^64 / 2^32
  47
  48 #define DEFINE_32BIT_PAIR_HASH(type1, type2) \
  49     DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) { \
  50       uint64 first = value.first; \
  51       uint32 second = value.second; \
  52       uint64 hash64 = (first << 32) | second; \
  53       \
  54       if (sizeof(std::size_t) >= sizeof(uint64)) \
  55         return static_cast<std::size_t>(hash64); \
  56       \
  57       uint64 odd_random = 481046412LL << 32 | 1025306954LL; \
  58       uint32 shift_random = 10121U << 16; \
  59       \
  60       hash64 = hash64 * odd_random + shift_random; \
  61       std::size_t high_bits = static_cast<std::size_t>( \
  62           hash64 >> (sizeof(uint64) - sizeof(std::size_t))); \
  63       return high_bits; \
  64     } \
  65   DEFINE_PAIR_HASH_FUNCTION_END();
  66
  67 DEFINE_32BIT_PAIR_HASH(int16, int16);
  68 DEFINE_32BIT_PAIR_HASH(int16, uint16);
  69 DEFINE_32BIT_PAIR_HASH(int16, int32);
  70 DEFINE_32BIT_PAIR_HASH(int16, uint32);
  71 DEFINE_32BIT_PAIR_HASH(uint16, int16);
  72 DEFINE_32BIT_PAIR_HASH(uint16, uint16);
  73 DEFINE_32BIT_PAIR_HASH(uint16, int32);
  74 DEFINE_32BIT_PAIR_HASH(uint16, uint32);
  75 DEFINE_32BIT_PAIR_HASH(int32, int16);
  76 DEFINE_32BIT_PAIR_HASH(int32, uint16);
  77 DEFINE_32BIT_PAIR_HASH(int32, int32);
  78 DEFINE_32BIT_PAIR_HASH(int32, uint32);
  79 DEFINE_32BIT_PAIR_HASH(uint32, int16);
  80 DEFINE_32BIT_PAIR_HASH(uint32, uint16);
  81 DEFINE_32BIT_PAIR_HASH(uint32, int32);
  82 DEFINE_32BIT_PAIR_HASH(uint32, uint32);
  83
  84 #undef DEFINE_32BIT_PAIR_HASH
  85
  86 // Implement hashing for pairs of up-to 64-bit integer values.
  87 // We use the compound integer hash method to produce a 64-bit hash code, by
  88 // breaking the two 64-bit inputs into 4 32-bit values:
  89 // http://opendatastructures.org/versions/edition-0.1d/ods-java/node33.html#SECTION00832000000000000000
  90 // Then we reduce our result to 32 bits if required, similar to above.
  91
  92 #define DEFINE_64BIT_PAIR_HASH(type1, type2) \
  93     DEFINE_PAIR_HASH_FUNCTION_START(type1, type2) { \
  94       uint32 short_random1 = 842304669U; \
  95       uint32 short_random2 = 619063811U; \
  96       uint32 short_random3 = 937041849U; \
  97       uint32 short_random4 = 3309708029U; \
  98       \
  99       uint64 value1 = value.first; \
 100       uint64 value2 = value.second; \
 101       uint32 value1a = static_cast<uint32>(value1 & 0xffffffff); \
 102       uint32 value1b = static_cast<uint32>((value1 >> 32) & 0xffffffff); \
 103       uint32 value2a = static_cast<uint32>(value2 & 0xffffffff); \
 104       uint32 value2b = static_cast<uint32>((value2 >> 32) & 0xffffffff); \
 105       \
 106       uint64 product1 = static_cast<uint64>(value1a) * short_random1; \
 107       uint64 product2 = static_cast<uint64>(value1b) * short_random2; \
 108       uint64 product3 = static_cast<uint64>(value2a) * short_random3; \
 109       uint64 product4 = static_cast<uint64>(value2b) * short_random4; \
 110       \
 111       uint64 hash64 = product1 + product2 + product3 + product4; \
 112       \
 113       if (sizeof(std::size_t) >= sizeof(uint64)) \
 114         return static_cast<std::size_t>(hash64); \
 115       \
 116       uint64 odd_random = 1578233944LL << 32 | 194370989LL; \
 117       uint32 shift_random = 20591U << 16; \
 118       \
 119       hash64 = hash64 * odd_random + shift_random; \
 120       std::size_t high_bits = static_cast<std::size_t>( \
 121           hash64 >> (sizeof(uint64) - sizeof(std::size_t))); \
 122       return high_bits; \
 123     } \
 124   DEFINE_PAIR_HASH_FUNCTION_END();
 125
 126 DEFINE_64BIT_PAIR_HASH(int16, int64);
 127 DEFINE_64BIT_PAIR_HASH(int16, uint64);
 128 DEFINE_64BIT_PAIR_HASH(uint16, int64);
 129 DEFINE_64BIT_PAIR_HASH(uint16, uint64);
 130 DEFINE_64BIT_PAIR_HASH(int32, int64);
 131 DEFINE_64BIT_PAIR_HASH(int32, uint64);
 132 DEFINE_64BIT_PAIR_HASH(uint32, int64);
 133 DEFINE_64BIT_PAIR_HASH(uint32, uint64);
 134 DEFINE_64BIT_PAIR_HASH(int64, int16);
 135 DEFINE_64BIT_PAIR_HASH(int64, uint16);
 136 DEFINE_64BIT_PAIR_HASH(int64, int32);
 137 DEFINE_64BIT_PAIR_HASH(int64, uint32);
 138 DEFINE_64BIT_PAIR_HASH(int64, int64);
 139 DEFINE_64BIT_PAIR_HASH(int64, uint64);
 140 DEFINE_64BIT_PAIR_HASH(uint64, int16);
 141 DEFINE_64BIT_PAIR_HASH(uint64, uint16);
 142 DEFINE_64BIT_PAIR_HASH(uint64, int32);
 143 DEFINE_64BIT_PAIR_HASH(uint64, uint32);
 144 DEFINE_64BIT_PAIR_HASH(uint64, int64);
 145 DEFINE_64BIT_PAIR_HASH(uint64, uint64);
 146
 147 #undef DEFINE_64BIT_PAIR_HASH
 148 }
 149
 150 #undef DEFINE_PAIR_HASH_FUNCTION_START
 151 #undef DEFINE_PAIR_HASH_FUNCTION_END
 152
 153 #endif  // CC_BASE_HASH_PAIR_H_