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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/containers/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#SECT
ION00832000000000000000 | |
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_ | |
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