text: // Copyright Kevlin Henney, 2000-2005.
  // Copyright Alexander Nasonov, 2006-2010.
  // Copyright Antony Polukhin, 2011-2016.
  //
  // 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)
  //
  // what:  lexical_cast custom keyword cast
  // who:   contributed by Kevlin Henney,
  //        enhanced with contributions from Terje Slettebo,
  //        with additional fixes and suggestions from Gennaro Prota,
  //        Beman Dawes, Dave Abrahams, Daryle Walker, Peter Dimov,
  //        Alexander Nasonov, Antony Polukhin, Justin Viiret, Michael Hofmann,
  //        Cheng Yang, Matthew Bradbury, David W. Birdsall, Pavel Korzh and other Boosters
  // when:  November 2000, March 2003, June 2005, June 2006, March 2011 - 2016
  
  #ifndef BOOST_LEXICAL_CAST_DETAIL_CONVERTER_NUMERIC_HPP
  #define BOOST_LEXICAL_CAST_DETAIL_CONVERTER_NUMERIC_HPP
  
  #include <boost/config.hpp>
  #ifdef BOOST_HAS_PRAGMA_ONCE
  #   pragma once
  #endif
  
  #include <boost/limits.hpp>
  #include <boost/mpl/eval_if.hpp>
  #include <boost/mpl/identity.hpp>
  #include <boost/mpl/if.hpp>
  #include <boost/type_traits/make_unsigned.hpp>
  #include <boost/type_traits/is_signed.hpp>
  #include <boost/type_traits/is_integral.hpp>
  #include <boost/type_traits/is_arithmetic.hpp>
  #include <boost/type_traits/is_base_of.hpp>
  #include <boost/type_traits/is_float.hpp>
  
  #include <boost/numeric/conversion/cast.hpp>
  
  namespace boost { namespace detail {
  
  template <class Source >
  struct detect_precision_loss
  {
      typedef Source source_type;
      typedef boost::numeric::Trunc<Source> Rounder;
      typedef BOOST_DEDUCED_TYPENAME mpl::if_<
          boost::is_arithmetic<Source>, Source, Source const&
      >::type argument_type ;
  
      static inline source_type nearbyint(argument_type s, bool& is_ok) BOOST_NOEXCEPT {
          const source_type near_int = Rounder::nearbyint(s);
          if (near_int && is_ok) {
              const source_type orig_div_round = s / near_int;
              const source_type eps = std::numeric_limits<source_type>::epsilon();
  
              is_ok = !((orig_div_round > 1 ? orig_div_round - 1 : 1 - orig_div_round) > eps);
          }
  
          return s;
      }
  
      typedef typename Rounder::round_style round_style;
  };
  
  template <typename Base, class Source>
  struct fake_precision_loss: public Base
  {
      typedef Source source_type ;
      typedef BOOST_DEDUCED_TYPENAME mpl::if_<
          boost::is_arithmetic<Source>, Source, Source const&
      >::type argument_type ;
  
      static inline source_type nearbyint(argument_type s, bool& /*is_ok*/) BOOST_NOEXCEPT {
          return s;
      }
  };
  
  struct nothrow_overflow_handler
  {
      inline bool operator() ( boost::numeric::range_check_result r ) const BOOST_NOEXCEPT {
          return (r == boost::numeric::cInRange);
      }
  };
  
  template <typename Target, typename Source>
  inline bool noexcept_numeric_convert(const Source& arg, Target& result) BOOST_NOEXCEPT {
      typedef boost::numeric::converter<
              Target,
              Source,
              boost::numeric::conversion_traits<Target, Source >,
              nothrow_overflow_handler,
              detect_precision_loss<Source >
      > converter_orig_t;
  
      typedef BOOST_DEDUCED_TYPENAME boost::mpl::if_c<
          boost::is_base_of< detect_precision_loss<Source >, converter_orig_t >::value,
          converter_orig_t,
          fake_precision_loss<converter_orig_t, Source>
      >::type converter_t;
  
      bool res = nothrow_overflow_handler()(converter_t::out_of_range(arg));
      result = converter_t::low_level_convert(converter_t::nearbyint(arg, res));
      return res;
  }
  
  template <typename Target, typename Source>
  struct lexical_cast_dynamic_num_not_ignoring_minus
  {
      static inline bool try_convert(const Source &arg, Target& result) BOOST_NOEXCEPT {
          return noexcept_numeric_convert<Target, Source >(arg, result);
      }
  };
  
  template <typename Target, typename Source>
  struct lexical_cast_dynamic_num_ignoring_minus
  {
      static inline bool try_convert(const Source &arg, Target& result) BOOST_NOEXCEPT {
          typedef BOOST_DEDUCED_TYPENAME boost::mpl::eval_if_c<
                  boost::is_float<Source>::value,
                  boost::mpl::identity<Source>,
                  boost::make_unsigned<Source>
          >::type usource_t;
  
          if (arg < 0) {
              const bool res = noexcept_numeric_convert<Target, usource_t>(0u - arg, result);
              result = static_cast<Target>(0u - result);
              return res;
          } else {
              return noexcept_numeric_convert<Target, usource_t>(arg, result);
          }
      }
  };
  
  /*
   * lexical_cast_dynamic_num follows the rules:
   * 1) If Source can be converted to Target without precision loss and
   * without overflows, then assign Source to Target and return
   *
   * 2) If Source is less than 0 and Target is an unsigned integer,
   * then negate Source, check the requirements of rule 1) and if
   * successful, assign static_casted Source to Target and return
   *
   * 3) Otherwise throw a bad_lexical_cast exception
   *
   *
   * Rule 2) required because boost::lexical_cast has the behavior of
   * stringstream, which uses the rules of scanf for conversions. And
   * in the C99 standard for unsigned input value minus sign is
   * optional, so if a negative number is read, no errors will arise
   * and the result will be the two's complement.
   */
  template <typename Target, typename Source>
  struct dynamic_num_converter_impl
  {
      static inline bool try_convert(const Source &arg, Target& result) BOOST_NOEXCEPT {
          typedef BOOST_DEDUCED_TYPENAME boost::mpl::if_c<
              boost::is_unsigned<Target>::value &&
              (boost::is_signed<Source>::value || boost::is_float<Source>::value) &&
              !(boost::is_same<Source, bool>::value) &&
              !(boost::is_same<Target, bool>::value),
              lexical_cast_dynamic_num_ignoring_minus<Target, Source>,
              lexical_cast_dynamic_num_not_ignoring_minus<Target, Source>
          >::type caster_type;
  
          return caster_type::try_convert(arg, result);
      }
  };
  
  }} // namespace boost::detail
  
  #endif // BOOST_LEXICAL_CAST_DETAIL_CONVERTER_NUMERIC_HPP
  
  