libs/core/src/eu/core/hash.h
| Line | Branch | Exec | Source |
|---|---|---|---|
| 1 | #pragma once | ||
| 2 | |||
| 3 | namespace eu::core | ||
| 4 | { | ||
| 5 | |||
| 6 | /** \addtogroup hash Hash-util | ||
| 7 | * \brief Helper macros for specializing the std::hash. | ||
| 8 | * This group provides a util \ref HashCombiner to simplify the creation of hash functions | ||
| 9 | * for user-defined types (using std::hash) and macros for specialization of std::hash for custom types. | ||
| 10 | * | ||
| 11 | * Example usage: | ||
| 12 | * ``` | ||
| 13 | * HASH_DEF_BEGIN(MyType) | ||
| 14 | * HASH_DEF(member1) | ||
| 15 | * HASH_DEF(member2) | ||
| 16 | * HASH_DEF_END() | ||
| 17 | * ``` | ||
| 18 | * @{ | ||
| 19 | */ | ||
| 20 | |||
| 21 | |||
| 22 | /// A utility for combining hash values of multiple objects into a single hash value. | ||
| 23 | /// \note | ||
| 24 | /// Do not use when hashing is critical. | ||
| 25 | struct HashCombiner | ||
| 26 | { | ||
| 27 | std::size_t result = 17; | ||
| 28 | |||
| 29 | /// Combines the hash of the given object with the current result. | ||
| 30 | /// | ||
| 31 | /// src: https://stackoverflow.com/a/17017281/180307 | ||
| 32 | /// numbers from: https://stackoverflow.com/a/1646913/180307 | ||
| 33 | /// \note | ||
| 34 | /// A word of warning, this is (a variation of) the Berstein hash, and because nobody | ||
| 35 | /// knows why it does well in tests it is not advisable when hashing is critical. | ||
| 36 | /// See https://github.com/mignon-p/jsw-libs/blob/master/Tutorials/jsw_tut_hashing.md | ||
| 37 | template<typename T> | ||
| 38 | ✗ | HashCombiner& combine(const T& t) | |
| 39 | { | ||
| 40 | ✗ | result = result * 31 + std::hash<T>{}(t); | |
| 41 | ✗ | return *this; | |
| 42 | } | ||
| 43 | }; | ||
| 44 | |||
| 45 | |||
| 46 | /** Begins the definition of a specialization of std::hash for the given TYPE. | ||
| 47 | * Should be closed by the \ref HASH_DEF_END macro | ||
| 48 | * @param TYPE The user-defined type for which the hash specialization is being created. | ||
| 49 | * \hideinlinesource | ||
| 50 | */ | ||
| 51 | #define HASH_DEF_BEGIN(TYPE) \ | ||
| 52 | template<> \ | ||
| 53 | struct std::hash<TYPE> \ | ||
| 54 | { \ | ||
| 55 | std::size_t operator()(const TYPE& x) const \ | ||
| 56 | { \ | ||
| 57 | return eu::core::HashCombiner \ | ||
| 58 | { \ | ||
| 59 | } | ||
| 60 | |||
| 61 | /** Adds the hash of a member variable to the hash combination. | ||
| 62 | * \hideinlinesource | ||
| 63 | * | ||
| 64 | * This macro should be used within a \ref HASH_DEF_BEGIN and \ref HASH_DEF_END block to combine | ||
| 65 | * the hash of a specific member variable of the type. | ||
| 66 | * | ||
| 67 | * | ||
| 68 | * @param NAME The name of the member variable to include in the hash. | ||
| 69 | */ | ||
| 70 | #define HASH_DEF(NAME) .combine(x.NAME) | ||
| 71 | |||
| 72 | /** Ends the definition of the std::hash specialization. | ||
| 73 | * | ||
| 74 | * This macro should be used to close the hash function definition started with | ||
| 75 | * \ref HASH_DEF_BEGIN. It returns the final combined hash value. | ||
| 76 | * | ||
| 77 | * \hideinlinesource | ||
| 78 | */ | ||
| 79 | #define HASH_DEF_END() \ | ||
| 80 | .result; \ | ||
| 81 | } \ | ||
| 82 | } \ | ||
| 83 | ; | ||
| 84 | |||
| 85 | /** | ||
| 86 | * @} | ||
| 87 | */ | ||
| 88 | |||
| 89 | } // namespace klotter | ||
| 90 | |||
| 91 |