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 #ifndef BASE_HASH_H_
6 #define BASE_HASH_H_
7
8 #include <stddef.h>
9 #include <stdint.h>
10
11 #include <limits>
12 #include <string>
13 #include <utility>
14
15 #include "base/base_export.h"
16 #include "base/logging.h"
17 #include "base/strings/string16.h"
18
19 namespace base {
20
21 // Computes a hash of a memory buffer. This hash function is subject to change
22 // in the future, so use only for temporary in-memory structures. If you need
23 // to persist a change on disk or between computers, use PersistentHash().
24 //
25 // WARNING: This hash function should not be used for any cryptographic purpose.
26 BASE_EXPORT uint32_t Hash(const void* data, size_t length);
27 BASE_EXPORT uint32_t Hash(const std::string& str);
28 BASE_EXPORT uint32_t Hash(const string16& str);
29
30 // Computes a hash of a memory buffer. This hash function must not change so
31 // that code can use the hashed values for persistent storage purposes or
32 // sending across the network. If a new persistent hash function is desired, a
33 // new version will have to be added in addition.
34 //
35 // WARNING: This hash function should not be used for any cryptographic purpose.
36 BASE_EXPORT uint32_t PersistentHash(const void* data, size_t length);
37 BASE_EXPORT uint32_t PersistentHash(const std::string& str);
38
39 // Hash pairs of 32-bit or 64-bit numbers.
40 BASE_EXPORT size_t HashInts32(uint32_t value1, uint32_t value2);
41 BASE_EXPORT size_t HashInts64(uint64_t value1, uint64_t value2);
42
43 template <typename T1, typename T2>
HashInts(T1 value1,T2 value2)44 inline size_t HashInts(T1 value1, T2 value2) {
45 // This condition is expected to be compile-time evaluated and optimised away
46 // in release builds.
47 if (sizeof(T1) > sizeof(uint32_t) || (sizeof(T2) > sizeof(uint32_t)))
48 return HashInts64(value1, value2);
49
50 return HashInts32(value1, value2);
51 }
52
53 // A templated hasher for pairs of integer types. Example:
54 //
55 // using MyPair = std::pair<int32_t, int32_t>;
56 // std::unordered_set<MyPair, base::IntPairHash<MyPair>> set;
57 template <typename T>
58 struct IntPairHash;
59
60 template <typename Type1, typename Type2>
61 struct IntPairHash<std::pair<Type1, Type2>> {
62 size_t operator()(std::pair<Type1, Type2> value) const {
63 return HashInts(value.first, value.second);
64 }
65 };
66
67 } // namespace base
68
69 #endif // BASE_HASH_H_
70