1 // Copyright 2011 The Chromium Authors
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_HASH_H_
6 #define BASE_HASH_HASH_H_
7
8 #include <stddef.h>
9 #include <stdint.h>
10
11 #include <limits>
12 #include <string>
13 #include <string_view>
14 #include <utility>
15
16 #include "base/base_export.h"
17 #include "base/containers/span.h"
18
19 namespace base {
20
21 // WARNING: These hash functions should not be used for any cryptographic
22 // purpose.
23
24 // Deprecated: Computes a hash of a memory buffer, use FastHash() instead.
25 // If you need to persist a change on disk or between computers, use
26 // PersistentHash().
27 // TODO(https://crbug.com/1025358): Migrate client code to new hash function.
28 BASE_EXPORT uint32_t Hash(const std::string& str);
29
30 // Really *fast* and high quality hash.
31 // Recommended hash function for general use, we pick the best performant
32 // hash for each build target.
33 // It is prone to be updated whenever a newer/faster hash function is
34 // publicly available.
35 // May changed without warning, do not expect stability of outputs.
36 BASE_EXPORT size_t FastHash(base::span<const uint8_t> data);
FastHash(std::string_view str)37 inline size_t FastHash(std::string_view str) {
38 return FastHash(as_bytes(make_span(str)));
39 }
40
41 // Computes a hash of a memory buffer. This hash function must not change so
42 // that code can use the hashed values for persistent storage purposes or
43 // sending across the network. If a new persistent hash function is desired, a
44 // new version will have to be added in addition.
45 //
46 // WARNING: This hash function should not be used for any cryptographic purpose.
47 BASE_EXPORT uint32_t PersistentHash(base::span<const uint8_t> data);
48 BASE_EXPORT uint32_t PersistentHash(std::string_view str);
49
50 // Hash pairs of 32-bit or 64-bit numbers.
51 BASE_EXPORT size_t HashInts32(uint32_t value1, uint32_t value2);
52 BASE_EXPORT size_t HashInts64(uint64_t value1, uint64_t value2);
53
54 template <typename T1, typename T2>
HashInts(T1 value1,T2 value2)55 inline size_t HashInts(T1 value1, T2 value2) {
56 // This condition is expected to be compile-time evaluated and optimised away
57 // in release builds.
58 if (sizeof(T1) > sizeof(uint32_t) || (sizeof(T2) > sizeof(uint32_t)))
59 return HashInts64(value1, value2);
60
61 return HashInts32(static_cast<uint32_t>(value1),
62 static_cast<uint32_t>(value2));
63 }
64
65 // A templated hasher for pairs of integer types. Example:
66 //
67 // using MyPair = std::pair<int32_t, int32_t>;
68 // std::unordered_set<MyPair, base::IntPairHash<MyPair>> set;
69 template <typename T>
70 struct IntPairHash;
71
72 template <typename Type1, typename Type2>
73 struct IntPairHash<std::pair<Type1, Type2>> {
74 size_t operator()(std::pair<Type1, Type2> value) const {
75 return HashInts(value.first, value.second);
76 }
77 };
78
79 } // namespace base
80
81 #endif // BASE_HASH_HASH_H_
82