source: downloads/boost_1_34_1/boost/functional/detail/hash_float.hpp @ 29

//  Copyright Daniel James 2005-2006. Use, modification, and distribution are
//  subject to 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)

//  Based on Peter Dimov's proposal
//  http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1756.pdf
//  issue 6.18. 

#if !defined(BOOST_FUNCTIONAL_DETAIL_HASH_FLOAT_HEADER)
#define BOOST_FUNCTIONAL_DETAIL_HASH_FLOAT_HEADER

#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once
#endif

#include <boost/functional/detail/float_functions.hpp>
#include <boost/limits.hpp>
#include <boost/assert.hpp>
#include <errno.h>

// Don't use fpclassify or _fpclass for stlport.
#if !defined(__SGI_STL_PORT) && !defined(_STLPORT_VERSION)
#  if defined(__GLIBCPP__) || defined(__GLIBCXX__)
// GNU libstdc++ 3
#    if (defined(__USE_ISOC99) || defined(_GLIBCXX_USE_C99_MATH)) && \
        !(defined(macintosh) || defined(__APPLE__) || defined(__APPLE_CC__))
#      define BOOST_HASH_USE_FPCLASSIFY
#    endif
#  elif (defined(_YVALS) && !defined(__IBMCPP__)) || defined(_CPPLIB_VER)
// Dinkumware Library, on Visual C++ 
#    if defined(BOOST_MSVC)
#      define BOOST_HASH_USE_FPCLASS
#    endif
#  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_impl(T v)
        {
            int exp = 0;
            errno = 0;
            v = boost::hash_detail::call_frexp(v, &exp);
            if(errno) return 0;

            std::size_t seed = 0;

            std::size_t const length
                = (std::numeric_limits<T>::digits +
                        std::numeric_limits<int>::digits - 1)
                / std::numeric_limits<int>::digits;

            for(std::size_t i = 0; i < length; ++i)
            {
                v = boost::hash_detail::call_ldexp(v, std::numeric_limits<int>::digits);
                int const part = static_cast<int>(v);
                v -= part;
                hash_float_combine(seed, part);
            }

            hash_float_combine(seed, exp);

            return seed;
        }

        template <class T>
        inline std::size_t float_hash_value(T v)
        {
#if defined(BOOST_HASH_USE_FPCLASSIFY)
            using namespace std;
            switch (fpclassify(v)) {
            case FP_ZERO:
                return 0;
            case FP_INFINITE:
                return (std::size_t)(v > 0 ? -1 : -2);
            case FP_NAN:
                return (std::size_t)(-3);
            case FP_NORMAL:
            case FP_SUBNORMAL:
                return float_hash_impl(v);
            default:
                BOOST_ASSERT(0);
                return 0;
            }
#elif defined(BOOST_HASH_USE_FPCLASS)
            switch(_fpclass(v)) {
            case _FPCLASS_NZ:
            case _FPCLASS_PZ:
                return 0;
            case _FPCLASS_PINF:
                return (std::size_t)(-1);
            case _FPCLASS_NINF:
                return (std::size_t)(-2);
            case _FPCLASS_SNAN:
            case _FPCLASS_QNAN:
                return (std::size_t)(-3);
            case _FPCLASS_NN:
            case _FPCLASS_ND:
                return float_hash_impl(v);
            case _FPCLASS_PD:
            case _FPCLASS_PN:
                return float_hash_impl(v);
            default:
                BOOST_ASSERT(0);
                return 0;
            }
#else
            return float_hash_impl(v);
#endif
        }
    }
}

#endif