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      1 //  (C) Copyright John Maddock 2006.
      2 //  (C) Copyright Johan Rade 2006.
      3 //  (C) Copyright Paul A. Bristow 2011 (added changesign).
      4 
      5 //  Use, modification and distribution are subject to the
      6 //  Boost Software License, Version 1.0. (See accompanying file
      7 //  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
      8 
      9 #ifndef BOOST_MATH_TOOLS_SIGN_HPP
     10 #define BOOST_MATH_TOOLS_SIGN_HPP
     11 
     12 #ifdef _MSC_VER
     13 #pragma once
     14 #endif
     15 
     16 #include <boost/math/tools/config.hpp>
     17 #include <boost/math/special_functions/math_fwd.hpp>
     18 #include <boost/math/special_functions/detail/fp_traits.hpp>
     19 
     20 namespace boost{ namespace math{
     21 
     22 namespace detail {
     23 
     24   // signbit
     25 
     26 #ifdef BOOST_MATH_USE_STD_FPCLASSIFY
     27     template<class T>
     28     inline int signbit_impl(T x, native_tag const&)
     29     {
     30         return (std::signbit)(x);
     31     }
     32 #endif
     33 
     34     template<class T>
     35     inline int signbit_impl(T x, generic_tag<true> const&)
     36     {
     37         return x < 0;
     38     }
     39 
     40     template<class T>
     41     inline int signbit_impl(T x, generic_tag<false> const&)
     42     {
     43         return x < 0;
     44     }
     45 
     46     template<class T>
     47     inline int signbit_impl(T x, ieee_copy_all_bits_tag const&)
     48     {
     49         typedef BOOST_DEDUCED_TYPENAME fp_traits<T>::type traits;
     50 
     51         BOOST_DEDUCED_TYPENAME traits::bits a;
     52         traits::get_bits(x,a);
     53         return a & traits::sign ? 1 : 0;
     54     }
     55 
     56     template<class T>
     57     inline int signbit_impl(T x, ieee_copy_leading_bits_tag const&)
     58     {
     59         typedef BOOST_DEDUCED_TYPENAME fp_traits<T>::type traits;
     60 
     61         BOOST_DEDUCED_TYPENAME traits::bits a;
     62         traits::get_bits(x,a);
     63 
     64         return a & traits::sign ? 1 : 0;
     65     }
     66 
     67     // Changesign
     68 
     69     template<class T>
     70     inline T (changesign_impl)(T x, generic_tag<true> const&)
     71     {
     72         return -x;
     73     }
     74 
     75     template<class T>
     76     inline T (changesign_impl)(T x, generic_tag<false> const&)
     77     {
     78         return -x;
     79     }
     80 
     81 
     82     template<class T>
     83     inline T changesign_impl(T x, ieee_copy_all_bits_tag const&)
     84     {
     85         typedef BOOST_DEDUCED_TYPENAME fp_traits<T>::sign_change_type traits;
     86 
     87         BOOST_DEDUCED_TYPENAME traits::bits a;
     88         traits::get_bits(x,a);
     89         a ^= traits::sign;
     90         traits::set_bits(x,a);
     91         return x;
     92     }
     93 
     94     template<class T>
     95     inline T (changesign_impl)(T x, ieee_copy_leading_bits_tag const&)
     96     {
     97         typedef BOOST_DEDUCED_TYPENAME fp_traits<T>::sign_change_type traits;
     98 
     99         BOOST_DEDUCED_TYPENAME traits::bits a;
    100         traits::get_bits(x,a);
    101         a ^= traits::sign;
    102         traits::set_bits(x,a);
    103         return x;
    104     }
    105 
    106 
    107 }   // namespace detail
    108 
    109 template<class T> int (signbit)(T x)
    110 {
    111    typedef typename detail::fp_traits<T>::type traits;
    112    typedef typename traits::method method;
    113    typedef typename boost::is_floating_point<T>::type fp_tag;
    114    return detail::signbit_impl(x, method());
    115 }
    116 
    117 template <class T>
    118 inline int sign BOOST_NO_MACRO_EXPAND(const T& z)
    119 {
    120    return (z == 0) ? 0 : (boost::math::signbit)(z) ? -1 : 1;
    121 }
    122 
    123 template<class T> T (changesign)(const T& x)
    124 { //!< \brief return unchanged binary pattern of x, except for change of sign bit.
    125    typedef typename detail::fp_traits<T>::sign_change_type traits;
    126    typedef typename traits::method method;
    127    typedef typename boost::is_floating_point<T>::type fp_tag;
    128 
    129    return detail::changesign_impl(x, method());
    130 }
    131 
    132 template <class T>
    133 inline T copysign BOOST_NO_MACRO_EXPAND(const T& x, const T& y)
    134 {
    135    BOOST_MATH_STD_USING
    136    return (boost::math::signbit)(x) != (boost::math::signbit)(y) ? (boost::math::changesign)(x) : x;
    137 }
    138 
    139 } // namespace math
    140 } // namespace boost
    141 
    142 
    143 #endif // BOOST_MATH_TOOLS_SIGN_HPP
    144 
    145 
    146