hash.h (2951B)
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 #include "base/strings/string_piece.h" 19 20 namespace base { 21 22 // WARNING: This hash functions should not be used for any cryptographic 23 // purpose. 24 25 // Deprecated: Computes a hash of a memory buffer, use FastHash() instead. 26 // If you need to persist a change on disk or between computers, use 27 // PersistentHash(). 28 // TODO(https://crbug.com/1025358): Migrate client code to new hash function. 29 BASE_EXPORT uint32_t Hash(const void* data, size_t length); 30 BASE_EXPORT uint32_t Hash(const std::string& str); 31 32 // Really *fast* and high quality hash. 33 // Recommended hash function for general use, we pick the best performant 34 // hash for each build target. 35 // It is prone to be updated whenever a newer/faster hash function is 36 // publicly available. 37 // May changed without warning, do not expect stability of outputs. 38 BASE_EXPORT size_t FastHash(base::span<const uint8_t> data); 39 inline size_t FastHash(StringPiece str) { 40 return FastHash(as_bytes(make_span(str))); 41 } 42 43 // Computes a hash of a memory buffer. This hash function must not change so 44 // that code can use the hashed values for persistent storage purposes or 45 // sending across the network. If a new persistent hash function is desired, a 46 // new version will have to be added in addition. 47 // 48 // WARNING: This hash function should not be used for any cryptographic purpose. 49 BASE_EXPORT uint32_t PersistentHash(base::span<const uint8_t> data); 50 BASE_EXPORT uint32_t PersistentHash(const void* data, size_t length); 51 BASE_EXPORT uint32_t PersistentHash(std::string_view str); 52 53 // Hash pairs of 32-bit or 64-bit numbers. 54 BASE_EXPORT size_t HashInts32(uint32_t value1, uint32_t value2); 55 BASE_EXPORT size_t HashInts64(uint64_t value1, uint64_t value2); 56 57 template <typename T1, typename T2> 58 inline size_t HashInts(T1 value1, T2 value2) { 59 // This condition is expected to be compile-time evaluated and optimised away 60 // in release builds. 61 if (sizeof(T1) > sizeof(uint32_t) || (sizeof(T2) > sizeof(uint32_t))) 62 return HashInts64(value1, value2); 63 64 return HashInts32(static_cast<uint32_t>(value1), 65 static_cast<uint32_t>(value2)); 66 } 67 68 // A templated hasher for pairs of integer types. Example: 69 // 70 // using MyPair = std::pair<int32_t, int32_t>; 71 // std::unordered_set<MyPair, base::IntPairHash<MyPair>> set; 72 template <typename T> 73 struct IntPairHash; 74 75 template <typename Type1, typename Type2> 76 struct IntPairHash<std::pair<Type1, Type2>> { 77 size_t operator()(std::pair<Type1, Type2> value) const { 78 return HashInts(value.first, value.second); 79 } 80 }; 81 82 } // namespace base 83 84 #endif // BASE_HASH_HASH_H_