// 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 |