HashCombine.h File Reference

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Classes
struct	Hash< T >
	Fallback hash function that calls T::GetHash() More...
struct	Hash< float >
	A hash function for floats. More...
struct	Hash< double >
	A hash function for doubles. More...
struct	Hash< const char * >
	A hash function for character pointers. More...
struct	Hash< std::string_view >
	A hash function for std::string_view. More...
struct	Hash< String >
	A hash function for String. More...
struct	Hash< T * >
	A fallback function for generic pointers. More...

Macros
#define	JPH_DEFINE_TRIVIAL_HASH(type)
	Helper macro to define a hash function for trivial types.
#define	JPH_MAKE_HASH_STRUCT(type, name, ...)
#define	JPH_MAKE_HASHABLE(type, ...)

Functions
JPH_NAMESPACE_BEGIN uint64	HashBytes (const void *inData, uint inSize, uint64 inSeed=0xcbf29ce484222325UL)
constexpr uint64	HashString (const char *inString, uint64 inSeed=0xcbf29ce484222325UL)
uint64	Hash64 (uint64 inValue)
template<typename T >
void	HashCombine (uint64 &ioSeed, const T &inValue)
	Commonly used types.
template<typename FirstValue , typename... Values>
uint64	HashCombineArgs (const FirstValue &inFirstValue, Values... inValues)

Macro Definition Documentation

JPH_DEFINE_TRIVIAL_HASH

#define JPH_DEFINE_TRIVIAL_HASH

(

type

)

Value:

template <>                                                 \
struct Hash<type>                                           \
{                                                           \
    uint64      operator () (const type &inValue) const     \
    {                                                       \
        return HashBytes(&inValue, sizeof(inValue));        \
    }                                                       \
};

Helper macro to define a hash function for trivial types.

JPH_MAKE_HASH_STRUCT

#define JPH_MAKE_HASH_STRUCT	(		type,
			name,
			...
	)

Value:

    struct [[nodiscard]] name                               \
    {                                                       \
        ::JPH::uint64 operator()(const type &t) const       \
        {                                                   \
            return ::JPH::HashCombineArgs(__VA_ARGS__);     \
        }                                                   \
    };

JPH_MAKE_HASHABLE

#define JPH_MAKE_HASHABLE	(		type,
			...
	)

Value:

    JPH_SUPPRESS_WARNING_PUSH                               \
    JPH_SUPPRESS_WARNINGS                                   \
    namespace JPH                                           \
    {                                                       \
        template<>                                          \
        JPH_MAKE_HASH_STRUCT(type, Hash<type>, __VA_ARGS__) \
    }                                                       \
    namespace std                                           \
    {                                                       \
        template<>                                          \
        struct [[nodiscard]] hash<type>                     \
        {                                                   \
            std::size_t operator()(const type &t) const     \
            {                                               \
                return std::size_t(::JPH::Hash<type>{ }(t));\
            }                                               \
        };                                                  \
    }                                                       \
    JPH_SUPPRESS_WARNING_POP

Function Documentation

Hash64()

uint64 Hash64 ( uint64  inValue )

inline

A 64 bit hash function by Thomas Wang, Jan 1997 See: http://web.archive.org/web/20071223173210/http://www.concentric.net/~Ttwang/tech/inthash.htm

Parameters

inValue

Value to hash

Returns

Hash

HashBytes()

JPH_NAMESPACE_BEGIN uint64 HashBytes ( const void *  inData, uint  inSize, uint64  inSeed = 0xcbf29ce484222325UL  )

inline

Implements the FNV-1a hash algorithm

See also

https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function

Parameters

inData	Data block of bytes
inSize	Number of bytes
inSeed	Seed of the hash (can be used to pass in the hash of a previous operation, otherwise leave default)

Returns

Hash

HashCombine()

template<typename T >

void HashCombine ( uint64 &  ioSeed, const T &  inValue  )

inline

Commonly used types.

Helper function that hashes a single value into ioSeed Taken from: https://stackoverflow.com/questions/2590677/how-do-i-combine-hash-values-in-c0x

HashCombineArgs()

template<typename FirstValue , typename... Values>

uint64 HashCombineArgs ( const FirstValue &  inFirstValue, Values...  inValues  )

inline

Hash combiner to use a custom struct in an unordered map or set

Usage:

struct SomeHashKey
{
    std::string key1;
    std::string key2;
    bool key3;
};

JPH_MAKE_HASHABLE(SomeHashKey, t.key1, t.key2, t.key3) 

HashString()

constexpr uint64 HashString ( const char *  inString, uint64  inSeed = 0xcbf29ce484222325UL  )

constexpr

Calculate the FNV-1a hash of inString.

See also

https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function