| |
| // 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 -= 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 -= 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 |