1 /*
2  * Copyright 2015 Google Inc. All rights reserved.
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *     http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef FLATBUFFERS_HASH_H_
18 #define FLATBUFFERS_HASH_H_
19 
20 #include <cstdint>
21 #include <cstring>
22 
23 #include "flatbuffers/flatbuffers.h"
24 
25 namespace flatbuffers {
26 
27 template<typename T> struct FnvTraits {
28   static const T kFnvPrime;
29   static const T kOffsetBasis;
30 };
31 
32 template<> struct FnvTraits<uint32_t> {
33   static const uint32_t kFnvPrime = 0x01000193;
34   static const uint32_t kOffsetBasis = 0x811C9DC5;
35 };
36 
37 template<> struct FnvTraits<uint64_t> {
38   static const uint64_t kFnvPrime = 0x00000100000001b3ULL;
39   static const uint64_t kOffsetBasis = 0xcbf29ce484222645ULL;
40 };
41 
42 template<typename T> T HashFnv1(const char *input) {
43   T hash = FnvTraits<T>::kOffsetBasis;
44   for (const char *c = input; *c; ++c) {
45     hash *= FnvTraits<T>::kFnvPrime;
46     hash ^= static_cast<unsigned char>(*c);
47   }
48   return hash;
49 }
50 
51 template<typename T> T HashFnv1a(const char *input) {
52   T hash = FnvTraits<T>::kOffsetBasis;
53   for (const char *c = input; *c; ++c) {
54     hash ^= static_cast<unsigned char>(*c);
55     hash *= FnvTraits<T>::kFnvPrime;
56   }
57   return hash;
58 }
59 
60 template<> inline uint16_t HashFnv1<uint16_t>(const char *input) {
61   uint32_t hash = HashFnv1<uint32_t>(input);
62   return (hash >> 16) ^ (hash & 0xffff);
63 }
64 
65 template<> inline uint16_t HashFnv1a<uint16_t>(const char *input) {
66   uint32_t hash = HashFnv1a<uint32_t>(input);
67   return (hash >> 16) ^ (hash & 0xffff);
68 }
69 
70 template<typename T> struct NamedHashFunction {
71   const char *name;
72 
73   typedef T (*HashFunction)(const char *);
74   HashFunction function;
75 };
76 
77 const NamedHashFunction<uint16_t> kHashFunctions16[] = {
78   { "fnv1_16", HashFnv1<uint16_t> },
79   { "fnv1a_16", HashFnv1a<uint16_t> },
80 };
81 
82 const NamedHashFunction<uint32_t> kHashFunctions32[] = {
83   { "fnv1_32", HashFnv1<uint32_t> },
84   { "fnv1a_32", HashFnv1a<uint32_t> },
85 };
86 
87 const NamedHashFunction<uint64_t> kHashFunctions64[] = {
88   { "fnv1_64", HashFnv1<uint64_t> },
89   { "fnv1a_64", HashFnv1a<uint64_t> },
90 };
91 
92 inline NamedHashFunction<uint16_t>::HashFunction FindHashFunction16(
93     const char *name) {
94   std::size_t size = sizeof(kHashFunctions16) / sizeof(kHashFunctions16[0]);
95   for (std::size_t i = 0; i < size; ++i) {
96     if (std::strcmp(name, kHashFunctions16[i].name) == 0) {
97       return kHashFunctions16[i].function;
98     }
99   }
100   return nullptr;
101 }
102 
103 inline NamedHashFunction<uint32_t>::HashFunction FindHashFunction32(
104     const char *name) {
105   std::size_t size = sizeof(kHashFunctions32) / sizeof(kHashFunctions32[0]);
106   for (std::size_t i = 0; i < size; ++i) {
107     if (std::strcmp(name, kHashFunctions32[i].name) == 0) {
108       return kHashFunctions32[i].function;
109     }
110   }
111   return nullptr;
112 }
113 
114 inline NamedHashFunction<uint64_t>::HashFunction FindHashFunction64(
115     const char *name) {
116   std::size_t size = sizeof(kHashFunctions64) / sizeof(kHashFunctions64[0]);
117   for (std::size_t i = 0; i < size; ++i) {
118     if (std::strcmp(name, kHashFunctions64[i].name) == 0) {
119       return kHashFunctions64[i].function;
120     }
121   }
122   return nullptr;
123 }
124 
125 }  // namespace flatbuffers
126 
127 #endif  // FLATBUFFERS_HASH_H_
128