1 // Copyright 2016 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 MOJO_PUBLIC_CPP_BINDINGS_LIB_HASH_UTIL_H_
6 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_HASH_UTIL_H_
7
8 #include <cstring>
9 #include <functional>
10 #include <type_traits>
11 #include <vector>
12
13 #include "base/optional.h"
14 #include "mojo/public/cpp/bindings/lib/template_util.h"
15
16 namespace mojo {
17 namespace internal {
18
19 template <typename T>
HashCombine(size_t seed,const T & value)20 size_t HashCombine(size_t seed, const T& value) {
21 // Based on proposal in:
22 // http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1756.pdf
23 return seed ^ (std::hash<T>()(value) + (seed << 6) + (seed >> 2));
24 }
25
26 template <typename T>
27 struct HasHashMethod {
28 template <typename U>
29 static char Test(decltype(&U::Hash));
30 template <typename U>
31 static int Test(...);
32 static const bool value = sizeof(Test<T>(0)) == sizeof(char);
33
34 private:
35 EnsureTypeIsComplete<T> check_t_;
36 };
37
38 template <typename T, bool has_hash_method = HasHashMethod<T>::value>
39 struct HashTraits;
40
41 template <typename T>
42 size_t Hash(size_t seed, const T& value);
43
44 template <typename T>
45 struct HashTraits<T, true> {
46 static size_t Hash(size_t seed, const T& value) { return value.Hash(seed); }
47 };
48
49 template <typename T>
50 struct HashTraits<T, false> {
51 static size_t Hash(size_t seed, const T& value) {
52 return HashCombine(seed, value);
53 }
54 };
55
56 template <typename T>
57 struct HashTraits<std::vector<T>, false> {
58 static size_t Hash(size_t seed, const std::vector<T>& value) {
59 for (const auto& element : value) {
60 seed = HashCombine(seed, element);
61 }
62 return seed;
63 }
64 };
65
66 template <typename T>
67 struct HashTraits<base::Optional<std::vector<T>>, false> {
68 static size_t Hash(size_t seed, const base::Optional<std::vector<T>>& value) {
69 if (!value)
70 return HashCombine(seed, 0);
71
72 return Hash(seed, *value);
73 }
74 };
75
76 template <typename T>
77 size_t Hash(size_t seed, const T& value) {
78 return HashTraits<T>::Hash(seed, value);
79 }
80
81 } // namespace internal
82 } // namespace mojo
83
84 #endif // MOJO_PUBLIC_CPP_BINDINGS_LIB_HASH_UTIL_H_
85