forked from boostorg/functional
Daniel James
534d526c90
1. hash_float is no longer dependent on the main hash header. 2. hash_float(0) == 0 which makes it easier to implement hash<complex>(), although this might lead to users assuming that it can be expected even though it isn't part of the documented interface. [SVN r32780]
62 lines
1.6 KiB
C++
62 lines
1.6 KiB
C++
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// (C) Copyright Daniel James 2005.
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// Use, modification and distribution are subject to the
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// Boost Software License, Version 1.0. (See accompanying file
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// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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// Based on Peter Dimov's proposal
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// http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1756.pdf
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// issue 6.18.
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#if !defined(BOOST_FUNCTIONAL_DETAIL_HASH_FLOAT_HEADER)
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#define BOOST_FUNCTIONAL_DETAIL_HASH_FLOAT_HEADER
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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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#include <boost/functional/detail/float_functions.hpp>
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#include <errno.h>
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#include <boost/limits.hpp>
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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_value(T v)
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{
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int exp = 0;
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errno = 0;
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v = boost::hash_detail::call_frexp(v, &exp);
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if(errno) return 0;
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std::size_t seed = 0;
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std::size_t const length
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= (std::numeric_limits<T>::digits +
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std::numeric_limits<int>::digits - 1)
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/ std::numeric_limits<int>::digits;
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for(std::size_t i = 0; i < length; ++i)
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{
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v = boost::hash_detail::call_ldexp(v, std::numeric_limits<int>::digits);
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int const part = static_cast<int>(v);
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v -= 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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}
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}
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#endif
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