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Make hash constexpr

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Probably doesn't add much directly, but it documents and
enforces the implied contract that the hash is fixed,
and could be used for, say, compile time hash tables.
This commit is contained in:
John Beard 2024-09-10 11:04:12 +01:00
parent 2815c99a2a
commit 80abdee90d
1 changed files with 6 additions and 8 deletions

14
libs/kimath/include/hash.h
View File

@ -22,8 +22,6 @@
*/
#pragma once
#ifndef LIBS_KIMATH_INCLUDE_HASH_H_
#define LIBS_KIMATH_INCLUDE_HASH_H_
#include <functional>
@ -31,7 +29,9 @@
* This is a dummy function to take the final case of hash_combine below
* @param seed
*/
static inline void hash_combine( std::size_t &seed ) {}
static inline constexpr void hash_combine( std::size_t& seed )
{
}
/**
* Combine multiple hashes utilizing previous hash result.
@ -40,19 +40,17 @@ static inline void hash_combine( std::size_t &seed ) {}
* @param seed A seed value input and output for the result.
* @param val A hashable object of type T
*/
template< typename T, typename ... Types >
static inline void hash_combine( std::size_t &seed, const T &val, const Types &... args )
template <typename T, typename... Types>
static inline constexpr void hash_combine( std::size_t& seed, const T& val, const Types&... args )
{
seed ^= std::hash<T>()( val ) + 0x9e3779b9 + ( seed << 6 ) + ( seed >> 2 );
hash_combine( seed, args... );
}
template <typename... Types>
static inline std::size_t hash_val( const Types &... args )
static inline constexpr std::size_t hash_val( const Types&... args )
{
std::size_t seed = 0xa82de1c0;
hash_combine( seed, args... );
return seed;
}
#endif /* LIBS_KIMATH_INCLUDE_HASH_H_ */