hash.h

#pragma once

using fnv_t = unsigned;

class fnv_hash
{
	static constexpr fnv_t FNV_PRIME = 16777619u;
	static constexpr fnv_t OFFSET_BASIS = 2166136261u;

	template <unsigned int N>
	static constexpr fnv_t fnvHashConst( const char( &str )[N], unsigned int I = N )
	{
		return static_cast<fnv_t>( 1ULL * ( I == 1 ? ( OFFSET_BASIS ^ str[0] ) : ( fnvHashConst( str, I - 1 ) ^ str[I - 1] ) ) * FNV_PRIME );
	}

	static __forceinline fnv_t fnvHash( const char* str )
	{
		const auto length = strlen( str ) + 1;
		auto hash = OFFSET_BASIS;
		for ( size_t i = 0; i < length; ++i )
		{
			hash ^= *str++;
			hash *= FNV_PRIME;
		}
		return hash;
	}

	struct Wrapper
	{
		Wrapper( const char* str ) : str( str ) { }
		const char* str;
	};

	fnv_t hash_value;
public:
	fnv_hash( Wrapper wrapper ) : hash_value( fnvHash( wrapper.str ) ) { }

	template <unsigned int N>
	constexpr fnv_hash( const char( &str )[N] ) : hash_value( fnvHashConst( str ) ) { }

	constexpr operator fnv_t( ) const { return this->hash_value; }
};