hash2/example/hash_with_any_seed.cpp

// Copyright 2024 Peter Dimov
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt

#include <boost/hash2/siphash.hpp>
#include <boost/hash2/hash_append.hpp>
#include <boost/hash2/get_integral_result.hpp>
#include <boost/unordered/unordered_flat_map.hpp>
#include <string>

template<class T, class H> class hash
{
private:

    H h_;

public:

    hash(): h_()
    {
    }

    explicit hash( std::uint64_t seed ): h_( seed )
    {
    }

    hash( unsigned char const* p, std::size_t n ): h_( p, n )
    {
    }

    std::size_t operator()( T const& v ) const
    {
        H h( h_ );
        boost::hash2::hash_append( h, {}, v );
        return boost::hash2::get_integral_result<std::size_t>( h );
    }
};

int main()
{
    using hasher = hash<std::string, boost::hash2::siphash_64>;

    {
        boost::unordered_flat_map<std::string, int, hasher> map;

        map[ "foo" ] = 1;
        map[ "bar" ] = 2;
    }

    {
        std::uint64_t seed = 0x0102030405060708ull;

        boost::unordered_flat_map<std::string, int, hasher> map( 0, hasher( seed ) );

        map[ "foo" ] = 1;
        map[ "bar" ] = 2;
    }

    {
        unsigned char const seed[ 16 ] =
        {
            0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
            0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10
        };

        boost::unordered_flat_map<std::string, int, hasher> map( 0, hasher(seed, sizeof(seed)) );

        map[ "foo" ] = 1;
        map[ "bar" ] = 2;
    }
}