libs/unordered/examples/fnv1.hpp
// Copyright 2008 Daniel James.
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
// This code is also released into the public domain.
// Algorithm from: http://www.isthe.com/chongo/tech/comp/fnv/
#include <string>
namespace hash
{
template <std::size_t FnvPrime, std::size_t OffsetBasis>
struct basic_fnv_1
{
std::size_t operator()(std::string const& text) const
{
std::size_t hash = OffsetBasis;
for(std::string::const_iterator it = text.begin(), end = text.end();
it != end; ++it)
{
hash *= FnvPrime;
hash ^= *it;
}
return hash;
}
};
template <std::size_t FnvPrime, std::size_t OffsetBasis>
struct basic_fnv_1a
{
std::size_t operator()(std::string const& text) const
{
std::size_t hash = OffsetBasis;
for(std::string::const_iterator it = text.begin(), end = text.end();
it != end; ++it)
{
hash ^= *it;
hash *= FnvPrime;
}
return hash;
}
};
// For 32 bit machines:
const std::size_t fnv_prime = 16777619u;
const std::size_t fnv_offset_basis = 2166136261u;
// For 64 bit machines:
// const std::size_t fnv_prime = 1099511628211u;
// const std::size_t fnv_offset_basis = 14695981039346656037u;
// For 128 bit machines:
// const std::size_t fnv_prime = 309485009821345068724781401u;
// const std::size_t fnv_offset_basis = 275519064689413815358837431229664493455u;
// For 256 bit machines:
// const std::size_t fnv_prime = 374144419156711147060143317175368453031918731002211u;
// const std::size_t fnv_offset_basis = 100029257958052580907070968620625704837092796014241193945225284501741471925557u;
typedef basic_fnv_1<fnv_prime, fnv_offset_basis> fnv_1;
typedef basic_fnv_1a<fnv_prime, fnv_offset_basis> fnv_1a;
}