92 lines
2.7 KiB
C++
92 lines
2.7 KiB
C++
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// Copyright 2005-2009 Daniel James.
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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// A general purpose hash function for non-zero floating point values.
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#if !defined(BOOST_FUNCTIONAL_HASH_DETAIL_HASH_FLOAT_GENERIC_HEADER)
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#define BOOST_FUNCTIONAL_HASH_DETAIL_HASH_FLOAT_GENERIC_HEADER
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#include <boost/functional/hash/detail/float_functions.hpp>
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#include <boost/integer/static_log2.hpp>
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#include <boost/functional/hash/detail/limits.hpp>
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#if defined(_MSC_VER) && (_MSC_VER >= 1020)
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# pragma once
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#endif
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#if defined(BOOST_MSVC)
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#pragma warning(push)
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#if BOOST_MSVC >= 1400
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#pragma warning(disable:6294) // Ill-defined for-loop: initial condition does
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// not satisfy test. Loop body not executed
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#endif
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#endif
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namespace boost
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{
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namespace hash_detail
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{
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inline void hash_float_combine(std::size_t& seed, std::size_t value)
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{
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seed ^= value + (seed<<6) + (seed>>2);
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}
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template <class T>
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inline std::size_t float_hash_impl2(T v)
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{
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boost::hash_detail::call_frexp<T> frexp;
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boost::hash_detail::call_ldexp<T> ldexp;
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int exp = 0;
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v = frexp(v, &exp);
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// A postive value is easier to hash, so combine the
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// sign with the exponent and use the absolute value.
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if(v < 0) {
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v = -v;
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exp += limits<T>::max_exponent -
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limits<T>::min_exponent;
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}
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v = ldexp(v, limits<std::size_t>::digits);
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std::size_t seed = static_cast<std::size_t>(v);
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v -= static_cast<T>(seed);
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// ceiling(digits(T) * log2(radix(T))/ digits(size_t)) - 1;
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std::size_t const length
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= (limits<T>::digits *
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boost::static_log2<limits<T>::radix>::value
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+ limits<std::size_t>::digits - 1)
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/ limits<std::size_t>::digits;
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for(std::size_t i = 0; i != length; ++i)
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{
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v = ldexp(v, limits<std::size_t>::digits);
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std::size_t part = static_cast<std::size_t>(v);
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v -= static_cast<T>(part);
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hash_float_combine(seed, part);
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}
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hash_float_combine(seed, exp);
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return seed;
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}
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template <class T>
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inline std::size_t float_hash_impl(T v)
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{
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typedef BOOST_DEDUCED_TYPENAME select_hash_type<T>::type type;
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return float_hash_impl2(static_cast<type>(v));
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}
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}
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}
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#if defined(BOOST_MSVC)
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#pragma warning(pop)
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#endif
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#endif
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