hashing Namespace Reference

This namespace provides efficient algorithms for quickly hashing different types for checking identity with a very low collision probability. More...

Typedefs
typedef std::size_t	HashValue

Functions
void	hashCombine (HashValue &)
	Final iteration of the variadic template with no additional arguments. More...
template<class T , class... Rest>
void	hashCombine (HashValue &seed, const T &value, Rest... rest)
	Variadic template to hashing a combination with finite size see: https://stackoverflow.com/a/38140932. More...
template<class Container >
HashValue	hashLargeContainer (Container const &container)
	Hash function for sampling 10 points from a large container and hashing see: https://stackoverflow.com/a/37007715. More...
HashValue	hashCombine (const libMesh::Point &point)
	Hashing for Point. More...
HashValue	hashCombine (Real time, const libMesh::Point &point)
	Hashing for Point and time, useful for Functions. More...

Detailed Description

This namespace provides efficient algorithms for quickly hashing different types for checking identity with a very low collision probability.

Typedef Documentation

HashValue

typedef std::size_t hashing::HashValue

Definition at line 22 of file Hashing.h.

Function Documentation

hashCombine() [1/4]

void hashing::hashCombine ( HashValue &  )

inline

Final iteration of the variadic template with no additional arguments.

Definition at line 28 of file Hashing.h.

Referenced by hashCombine(), hashLargeContainer(), TEST(), and MemoizedFunctionInterface::value().

{
}

hashCombine() [2/4]

template<class T , class... Rest>

void hashing::hashCombine ( HashValue &  seed, const T &  value, Rest...  rest  )

inline

Variadic template to hashing a combination with finite size see: https://stackoverflow.com/a/38140932.

Definition at line 38 of file Hashing.h.

{
  std::hash<T> hasher;

  seed ^= hasher(value) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
  hashCombine(seed, rest...);
}

hashCombine() [3/4]

HashValue hashing::hashCombine ( const libMesh::Point &  point )

inline

Hashing for Point.

Definition at line 70 of file Hashing.h.

{
  // 'Magic seed' seed that provides entropy against the other hashCombine() seed
  HashValue seed = 3;

  hashCombine(seed, point(0), point(1), point(2));

  return seed;
}

hashCombine() [4/4]

HashValue hashing::hashCombine ( Real  time, const libMesh::Point &  point  )

inline

Hashing for Point and time, useful for Functions.

Definition at line 84 of file Hashing.h.

{
  // 'Magic seed' seed that provides entropy against the other hashCombine() seed
  HashValue seed = 42;

  hashCombine(seed, time, point(0), point(1), point(2));

  return seed;
}

hashLargeContainer()

template<class Container >

HashValue hashing::hashLargeContainer

(

Container const &

container

)

Hash function for sampling 10 points from a large container and hashing see: https://stackoverflow.com/a/37007715.

Definition at line 52 of file Hashing.h.

Referenced by TEST().

{
  std::size_t size = container.size();
  std::size_t stride = 1 + size / 10;
  HashValue seed = size;

  for (std::size_t i = 0; i < size; i += stride)
  {
    hashCombine(seed, container.data()[i]);
  }

  return seed;
}