92 lines
2.7 KiB
C++
92 lines
2.7 KiB
C++
|
|
// Copyright 2005-2009 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)
|
|
|
|
// A general purpose hash function for non-zero floating point values.
|
|
|
|
#if !defined(BOOST_FUNCTIONAL_HASH_DETAIL_HASH_FLOAT_GENERIC_HEADER)
|
|
#define BOOST_FUNCTIONAL_HASH_DETAIL_HASH_FLOAT_GENERIC_HEADER
|
|
|
|
#include <boost/functional/hash/detail/float_functions.hpp>
|
|
#include <boost/integer/static_log2.hpp>
|
|
#include <boost/functional/hash/detail/limits.hpp>
|
|
|
|
#if defined(_MSC_VER) && (_MSC_VER >= 1020)
|
|
# pragma once
|
|
#endif
|
|
|
|
#if defined(BOOST_MSVC)
|
|
#pragma warning(push)
|
|
#if BOOST_MSVC >= 1400
|
|
#pragma warning(disable:6294) // Ill-defined for-loop: initial condition does
|
|
// not satisfy test. Loop body not executed
|
|
#endif
|
|
#endif
|
|
|
|
namespace boost
|
|
{
|
|
namespace hash_detail
|
|
{
|
|
inline void hash_float_combine(std::size_t& seed, std::size_t value)
|
|
{
|
|
seed ^= value + (seed<<6) + (seed>>2);
|
|
}
|
|
|
|
template <class T>
|
|
inline std::size_t float_hash_impl2(T v)
|
|
{
|
|
boost::hash_detail::call_frexp<T> frexp;
|
|
boost::hash_detail::call_ldexp<T> ldexp;
|
|
|
|
int exp = 0;
|
|
|
|
v = frexp(v, &exp);
|
|
|
|
// A postive value is easier to hash, so combine the
|
|
// sign with the exponent and use the absolute value.
|
|
if(v < 0) {
|
|
v = -v;
|
|
exp += limits<T>::max_exponent -
|
|
limits<T>::min_exponent;
|
|
}
|
|
|
|
v = ldexp(v, limits<std::size_t>::digits);
|
|
std::size_t seed = static_cast<std::size_t>(v);
|
|
v -= static_cast<T>(seed);
|
|
|
|
// ceiling(digits(T) * log2(radix(T))/ digits(size_t)) - 1;
|
|
std::size_t const length
|
|
= (limits<T>::digits *
|
|
boost::static_log2<limits<T>::radix>::value
|
|
+ limits<std::size_t>::digits - 1)
|
|
/ limits<std::size_t>::digits;
|
|
|
|
for(std::size_t i = 0; i != length; ++i)
|
|
{
|
|
v = ldexp(v, limits<std::size_t>::digits);
|
|
std::size_t part = static_cast<std::size_t>(v);
|
|
v -= static_cast<T>(part);
|
|
hash_float_combine(seed, part);
|
|
}
|
|
|
|
hash_float_combine(seed, exp);
|
|
|
|
return seed;
|
|
}
|
|
|
|
template <class T>
|
|
inline std::size_t float_hash_impl(T v)
|
|
{
|
|
typedef BOOST_DEDUCED_TYPENAME select_hash_type<T>::type type;
|
|
return float_hash_impl2(static_cast<type>(v));
|
|
}
|
|
}
|
|
}
|
|
|
|
#if defined(BOOST_MSVC)
|
|
#pragma warning(pop)
|
|
#endif
|
|
|
|
#endif
|