Non-cryptographic Hashing

Tools and functions to compute non-cryptographics hashes, for instance to use them in std::unordered_map. More...

Collaboration diagram for Non-cryptographic Hashing:

Detailed Description

Tools and functions to compute non-cryptographics hashes, for instance to use them in std::unordered_map.

Classes
struct	EigenHasher< T >
	STL-compatible hasher for dense Eigen types (matrices, vectors, arrays). More...
struct	GenericHasher< T, PointerToMember >
	STL-compatible hasher for custom classes where you list the members to be hashed as template parameters. More...

Functions
uint64_t	murmur64 (const ByteBufferView &buffer) noexcept
	Computes the non-cryptographic 64-bit MurmurHash2 on the input data.
uint64_t	djb2 (const ByteBufferView &data) noexcept
	Computes the djb2 hash value of the input data.
template<typename T>
uint64_t	combineHash (uint64_t seed, const T &object) noexcept
	Computes the hash of object using std::hash<T> and combines it with an already existing 64bit hash.
template<>
uint64_t	combineHash (uint64_t seed, const uint64_t &hashToAdd) noexcept
	Combines existing 64bit hashes.
template<typename... Ts>
uint64_t	genericHash (const Ts &... objects) noexcept
	Convenience function to compute the combined hash of an arbitrary number of inputs.

Function Documentation

murmur64()

uint64_t murmur64 ( const ByteBufferView & buffer )

noexcept

#include <ImFusion/Core/Hashing.h>

Computes the non-cryptographic 64-bit MurmurHash2 on the input data.

MurmurHash2 exhibits excellent performance in terms of both computation speed and collision robustness and can therefore serve as default choice for all non-cryptographic applications.

See also

https://github.com/aappleby/smhasher/wiki

djb2()

uint64_t djb2 ( const ByteBufferView & data )

noexcept

#include <ImFusion/Core/Hashing.h>

Computes the djb2 hash value of the input data.

Warning

This simplistic hashing algorithm is both slower and more prone to collisions than murmur64() and should not be used for new code.

See also

http://www.cse.yorku.ca/~oz/hash.html

combineHash() [1/2]

template<typename T>

uint64_t combineHash ( uint64_t seed, const T & object )

inlinenoexcept

#include <ImFusion/Core/Hashing.h>

Computes the hash of object using std::hash<T> and combines it with an already existing 64bit hash.

Example usage:

uint64_t hash = combineHash(0, object1);
hash = combineHash(hash, object2);
hash = combineHash(hash, object3);

combineHash() [2/2]

template<>

uint64_t combineHash ( uint64_t seed, const uint64_t & hashToAdd )

inlinenoexcept

#include <ImFusion/Core/Hashing.h>

Combines existing 64bit hashes.

Example usage:

uint64_t hash = combineHash(0, std::hash<...>()(...));
hash = combineHash(hash, std::hash<...>()(...));
hash = combineHash(hash, std::hash<...>()(...));

genericHash()

template<typename... Ts>

uint64_t genericHash ( const Ts &... objects )

inlinenoexcept

#include <ImFusion/Core/Hashing.h>

Convenience function to compute the combined hash of an arbitrary number of inputs.

Computes the individual hash of each argument using std::hash and combines them through combineHash(). Example usage:

int i = ...;
double d = ...;
std::string s = ...;
uint64_t hash = genericHash(i, d, s);

See also

GenericHasher