1// Copyright (c) 2011 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
6//
7// Deal with the differences between Microsoft and GNU implemenations
8// of hash_map. Allows all platforms to use |base::hash_map| and
9// |base::hash_set|.
10//  eg:
11//   base::hash_map<int> my_map;
12//   base::hash_set<int> my_set;
13//
14// NOTE: It is an explicit non-goal of this class to provide a generic hash
15// function for pointers.  If you want to hash a pointers to a particular class,
16// please define the template specialization elsewhere (for example, in its
17// header file) and keep it specific to just pointers to that class.  This is
18// because identity hashes are not desirable for all types that might show up
19// in containers as pointers.
20
21#ifndef BASE_CONTAINERS_HASH_TABLES_H_
22#define BASE_CONTAINERS_HASH_TABLES_H_
23
24#include <stddef.h>
25#include <stdint.h>
26
27#include <utility>
28
29#include "base/strings/string16.h"
30#include "build/build_config.h"
31
32#if defined(COMPILER_MSVC)
33#include <unordered_map>
34#include <unordered_set>
35
36#define BASE_HASH_NAMESPACE std
37
38#elif defined(COMPILER_GCC)
39
40#define BASE_HASH_NAMESPACE base_hash
41
42// This is a hack to disable the gcc 4.4 warning about hash_map and hash_set
43// being deprecated.  We can get rid of this when we upgrade to VS2008 and we
44// can use <tr1/unordered_map> and <tr1/unordered_set>.
45#ifdef __DEPRECATED
46#define CHROME_OLD__DEPRECATED __DEPRECATED
47#undef __DEPRECATED
48#endif
49
50#include <ext/hash_map>
51#include <ext/hash_set>
52#define BASE_HASH_IMPL_NAMESPACE __gnu_cxx
53
54#include <string>
55
56#ifdef CHROME_OLD__DEPRECATED
57#define __DEPRECATED CHROME_OLD__DEPRECATED
58#undef CHROME_OLD__DEPRECATED
59#endif
60
61namespace BASE_HASH_NAMESPACE {
62
63// The pre-standard hash behaves like C++11's std::hash, except around pointers.
64// const char* is specialized to hash the C string and hash functions for
65// general T* are missing. Define a BASE_HASH_NAMESPACE::hash which aligns with
66// the C++11 behavior.
67
68template<typename T>
69struct hash {
70  std::size_t operator()(const T& value) const {
71    return BASE_HASH_IMPL_NAMESPACE::hash<T>()(value);
72  }
73};
74
75template<typename T>
76struct hash<T*> {
77  std::size_t operator()(T* value) const {
78    return BASE_HASH_IMPL_NAMESPACE::hash<uintptr_t>()(
79        reinterpret_cast<uintptr_t>(value));
80  }
81};
82
83// The GNU C++ library provides identity hash functions for many integral types,
84// but not for |long long|.  This hash function will truncate if |size_t| is
85// narrower than |long long|.  This is probably good enough for what we will
86// use it for.
87
88#define DEFINE_TRIVIAL_HASH(integral_type) \
89    template<> \
90    struct hash<integral_type> { \
91      std::size_t operator()(integral_type value) const { \
92        return static_cast<std::size_t>(value); \
93      } \
94    }
95
96DEFINE_TRIVIAL_HASH(long long);
97DEFINE_TRIVIAL_HASH(unsigned long long);
98
99#undef DEFINE_TRIVIAL_HASH
100
101// Implement string hash functions so that strings of various flavors can
102// be used as keys in STL maps and sets.  The hash algorithm comes from the
103// GNU C++ library, in <tr1/functional>.  It is duplicated here because GCC
104// versions prior to 4.3.2 are unable to compile <tr1/functional> when RTTI
105// is disabled, as it is in our build.
106
107#define DEFINE_STRING_HASH(string_type) \
108    template<> \
109    struct hash<string_type> { \
110      std::size_t operator()(const string_type& s) const { \
111        std::size_t result = 0; \
112        for (string_type::const_iterator i = s.begin(); i != s.end(); ++i) \
113          result = (result * 131) + *i; \
114        return result; \
115      } \
116    }
117
118DEFINE_STRING_HASH(std::string);
119DEFINE_STRING_HASH(base::string16);
120
121#undef DEFINE_STRING_HASH
122
123}  // namespace BASE_HASH_NAMESPACE
124
125#else  // COMPILER
126#error define BASE_HASH_NAMESPACE for your compiler
127#endif  // COMPILER
128
129namespace base {
130
131// On MSVC, use the C++11 containers.
132#if defined(COMPILER_MSVC)
133
134template<class Key, class T,
135         class Hash = std::hash<Key>,
136         class Pred = std::equal_to<Key>,
137         class Alloc = std::allocator<std::pair<const Key, T>>>
138using hash_map = std::unordered_map<Key, T, Hash, Pred, Alloc>;
139
140template<class Key, class T,
141         class Hash = std::hash<Key>,
142         class Pred = std::equal_to<Key>,
143         class Alloc = std::allocator<std::pair<const Key, T>>>
144using hash_multimap = std::unordered_multimap<Key, T, Hash, Pred, Alloc>;
145
146template<class Key,
147         class Hash = std::hash<Key>,
148         class Pred = std::equal_to<Key>,
149         class Alloc = std::allocator<Key>>
150using hash_multiset = std::unordered_multiset<Key, Hash, Pred, Alloc>;
151
152template<class Key,
153         class Hash = std::hash<Key>,
154         class Pred = std::equal_to<Key>,
155         class Alloc = std::allocator<Key>>
156using hash_set = std::unordered_set<Key, Hash, Pred, Alloc>;
157
158#else  // !COMPILER_MSVC
159
160// Otherwise, use the pre-standard ones, but override the default hash to match
161// C++11.
162template<class Key, class T,
163         class Hash = BASE_HASH_NAMESPACE::hash<Key>,
164         class Pred = std::equal_to<Key>,
165         class Alloc = std::allocator<std::pair<const Key, T>>>
166using hash_map = BASE_HASH_IMPL_NAMESPACE::hash_map<Key, T, Hash, Pred, Alloc>;
167
168template<class Key, class T,
169         class Hash = BASE_HASH_NAMESPACE::hash<Key>,
170         class Pred = std::equal_to<Key>,
171         class Alloc = std::allocator<std::pair<const Key, T>>>
172using hash_multimap =
173    BASE_HASH_IMPL_NAMESPACE::hash_multimap<Key, T, Hash, Pred, Alloc>;
174
175template<class Key,
176         class Hash = BASE_HASH_NAMESPACE::hash<Key>,
177         class Pred = std::equal_to<Key>,
178         class Alloc = std::allocator<Key>>
179using hash_multiset =
180    BASE_HASH_IMPL_NAMESPACE::hash_multiset<Key, Hash, Pred, Alloc>;
181
182template<class Key,
183         class Hash = BASE_HASH_NAMESPACE::hash<Key>,
184         class Pred = std::equal_to<Key>,
185         class Alloc = std::allocator<Key>>
186using hash_set = BASE_HASH_IMPL_NAMESPACE::hash_set<Key, Hash, Pred, Alloc>;
187
188#undef BASE_HASH_IMPL_NAMESPACE
189
190#endif  // COMPILER_MSVC
191
192// Implement hashing for pairs of at-most 32 bit integer values.
193// When size_t is 32 bits, we turn the 64-bit hash code into 32 bits by using
194// multiply-add hashing. This algorithm, as described in
195// Theorem 4.3.3 of the thesis "Über die Komplexität der Multiplikation in
196// eingeschränkten Branchingprogrammmodellen" by Woelfel, is:
197//
198//   h32(x32, y32) = (h64(x32, y32) * rand_odd64 + rand16 * 2^16) % 2^64 / 2^32
199//
200// Contact danakj@chromium.org for any questions.
201inline std::size_t HashInts32(uint32_t value1, uint32_t value2) {
202  uint64_t value1_64 = value1;
203  uint64_t hash64 = (value1_64 << 32) | value2;
204
205  if (sizeof(std::size_t) >= sizeof(uint64_t))
206    return static_cast<std::size_t>(hash64);
207
208  uint64_t odd_random = 481046412LL << 32 | 1025306955LL;
209  uint32_t shift_random = 10121U << 16;
210
211  hash64 = hash64 * odd_random + shift_random;
212  std::size_t high_bits = static_cast<std::size_t>(
213      hash64 >> (8 * (sizeof(uint64_t) - sizeof(std::size_t))));
214  return high_bits;
215}
216
217// Implement hashing for pairs of up-to 64-bit integer values.
218// We use the compound integer hash method to produce a 64-bit hash code, by
219// breaking the two 64-bit inputs into 4 32-bit values:
220// http://opendatastructures.org/versions/edition-0.1d/ods-java/node33.html#SECTION00832000000000000000
221// Then we reduce our result to 32 bits if required, similar to above.
222inline std::size_t HashInts64(uint64_t value1, uint64_t value2) {
223  uint32_t short_random1 = 842304669U;
224  uint32_t short_random2 = 619063811U;
225  uint32_t short_random3 = 937041849U;
226  uint32_t short_random4 = 3309708029U;
227
228  uint32_t value1a = static_cast<uint32_t>(value1 & 0xffffffff);
229  uint32_t value1b = static_cast<uint32_t>((value1 >> 32) & 0xffffffff);
230  uint32_t value2a = static_cast<uint32_t>(value2 & 0xffffffff);
231  uint32_t value2b = static_cast<uint32_t>((value2 >> 32) & 0xffffffff);
232
233  uint64_t product1 = static_cast<uint64_t>(value1a) * short_random1;
234  uint64_t product2 = static_cast<uint64_t>(value1b) * short_random2;
235  uint64_t product3 = static_cast<uint64_t>(value2a) * short_random3;
236  uint64_t product4 = static_cast<uint64_t>(value2b) * short_random4;
237
238  uint64_t hash64 = product1 + product2 + product3 + product4;
239
240  if (sizeof(std::size_t) >= sizeof(uint64_t))
241    return static_cast<std::size_t>(hash64);
242
243  uint64_t odd_random = 1578233944LL << 32 | 194370989LL;
244  uint32_t shift_random = 20591U << 16;
245
246  hash64 = hash64 * odd_random + shift_random;
247  std::size_t high_bits = static_cast<std::size_t>(
248      hash64 >> (8 * (sizeof(uint64_t) - sizeof(std::size_t))));
249  return high_bits;
250}
251
252template<typename T1, typename T2>
253inline std::size_t HashPair(T1 value1, T2 value2) {
254  // This condition is expected to be compile-time evaluated and optimised away
255  // in release builds.
256  if (sizeof(T1) > sizeof(uint32_t) || (sizeof(T2) > sizeof(uint32_t)))
257    return HashInts64(value1, value2);
258
259  return HashInts32(value1, value2);
260}
261
262}  // namespace base
263
264namespace BASE_HASH_NAMESPACE {
265
266// Implement methods for hashing a pair of integers, so they can be used as
267// keys in STL containers.
268
269template<typename Type1, typename Type2>
270struct hash<std::pair<Type1, Type2> > {
271  std::size_t operator()(std::pair<Type1, Type2> value) const {
272    return base::HashPair(value.first, value.second);
273  }
274};
275
276}  // namespace BASE_HASH_NAMESPACE
277
278#undef DEFINE_PAIR_HASH_FUNCTION_START
279#undef DEFINE_PAIR_HASH_FUNCTION_END
280
281#endif  // BASE_CONTAINERS_HASH_TABLES_H_
282