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30 
31 // Author: kenton@google.com (Kenton Varda)
32 
33 #ifndef GOOGLE_PROTOBUF_STUBS_HASH_H__
34 #define GOOGLE_PROTOBUF_STUBS_HASH_H__
35 
36 #include <string.h>
37 #include <google/protobuf/stubs/common.h>
38 
39 #include <unordered_map>
40 #include <unordered_set>
41 
42 # define GOOGLE_PROTOBUF_HASH_NAMESPACE_DECLARATION_START \
43   namespace google {                                      \
44   namespace protobuf {
45 # define GOOGLE_PROTOBUF_HASH_NAMESPACE_DECLARATION_END }}
46 
47 namespace google {
48 namespace protobuf {
49 
50 template <typename Key>
51 struct hash : public std::hash<Key> {};
52 
53 template <typename Key>
54 struct hash<const Key*> {
55   inline size_t operator()(const Key* key) const {
56     return reinterpret_cast<size_t>(key);
57   }
58 };
59 
60 // Unlike the old SGI version, the TR1 "hash" does not special-case char*.  So,
61 // we go ahead and provide our own implementation.
62 template <>
63 struct hash<const char*> {
64   inline size_t operator()(const char* str) const {
65     size_t result = 0;
66     for (; *str != '\0'; str++) {
67       result = 5 * result + static_cast<size_t>(*str);
68     }
69     return result;
70   }
71 };
72 
73 template<>
74 struct hash<bool> {
75   size_t operator()(bool x) const {
76     return static_cast<size_t>(x);
77   }
78 };
79 
80 template <>
81 struct hash<string> {
82   inline size_t operator()(const string& key) const {
83     return hash<const char*>()(key.c_str());
84   }
85 
86   static const size_t bucket_size = 4;
87   static const size_t min_buckets = 8;
88   inline bool operator()(const string& a, const string& b) const {
89     return a < b;
90   }
91 };
92 
93 template <typename First, typename Second>
94 struct hash<std::pair<First, Second> > {
95   inline size_t operator()(const std::pair<First, Second>& key) const {
96     size_t first_hash = hash<First>()(key.first);
97     size_t second_hash = hash<Second>()(key.second);
98 
99     // FIXME(kenton):  What is the best way to compute this hash?  I have
100     // no idea!  This seems a bit better than an XOR.
101     return first_hash * ((1 << 16) - 1) + second_hash;
102   }
103 
104   static const size_t bucket_size = 4;
105   static const size_t min_buckets = 8;
106   inline bool operator()(const std::pair<First, Second>& a,
107                            const std::pair<First, Second>& b) const {
108     return a < b;
109   }
110 };
111 
112 // Used by GCC/SGI STL only.  (Why isn't this provided by the standard
113 // library?  :( )
114 struct streq {
115   inline bool operator()(const char* a, const char* b) const {
116     return strcmp(a, b) == 0;
117   }
118 };
119 
120 }  // namespace protobuf
121 }  // namespace google
122 
123 #endif  // GOOGLE_PROTOBUF_STUBS_HASH_H__
124