text: // Copyright Kevlin Henney, 2000-2005.
  // Copyright Alexander Nasonov, 2006-2010.
  // Copyright Antony Polukhin, 2011-2014.
  //
  // 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 - 2014
  
  #ifndef BOOST_LEXICAL_CAST_DETAIL_LCAST_UNSIGNED_CONVERTERS_HPP
  #define BOOST_LEXICAL_CAST_DETAIL_LCAST_UNSIGNED_CONVERTERS_HPP
  
  #include <boost/config.hpp>
  #ifdef BOOST_HAS_PRAGMA_ONCE
  #   pragma once
  #endif
  
  #include <climits>
  #include <cstddef>
  #include <string>
  #include <cstring>
  #include <cstdio>
  #include <boost/limits.hpp>
  #include <boost/mpl/if.hpp>
  #include <boost/static_assert.hpp>
  #include <boost/detail/workaround.hpp>
  
  
  #ifndef BOOST_NO_STD_LOCALE
  #   include <locale>
  #else
  #   ifndef BOOST_LEXICAL_CAST_ASSUME_C_LOCALE
          // Getting error at this point means, that your STL library is old/lame/misconfigured.
          // If nothing can be done with STL library, define BOOST_LEXICAL_CAST_ASSUME_C_LOCALE,
          // but beware: lexical_cast will understand only 'C' locale delimeters and thousands
          // separators.
  #       error "Unable to use <locale> header. Define BOOST_LEXICAL_CAST_ASSUME_C_LOCALE to force "
  #       error "boost::lexical_cast to use only 'C' locale during conversions."
  #   endif
  #endif
  
  #include <boost/lexical_cast/detail/lcast_char_constants.hpp>
  #include <boost/type_traits/make_unsigned.hpp>
  #include <boost/type_traits/is_signed.hpp>
  #include <boost/noncopyable.hpp>
  
  namespace boost 
  {
      namespace detail // lcast_to_unsigned
      {
          template<class T>
          inline
          BOOST_DEDUCED_TYPENAME boost::make_unsigned<T>::type lcast_to_unsigned(const T value) BOOST_NOEXCEPT {
              typedef BOOST_DEDUCED_TYPENAME boost::make_unsigned<T>::type result_type;
              return value < 0 
                  ? static_cast<result_type>(0u - static_cast<result_type>(value)) 
                  : static_cast<result_type>(value);
          }
      }
  
      namespace detail // lcast_put_unsigned
      {
          template <class Traits, class T, class CharT>
          class lcast_put_unsigned: boost::noncopyable {
              typedef BOOST_DEDUCED_TYPENAME Traits::int_type int_type;
              BOOST_DEDUCED_TYPENAME boost::mpl::if_c<
                      (sizeof(int_type) > sizeof(T))
                      , int_type
                      , T
              >::type         m_value;
              CharT*          m_finish;
              CharT    const  m_czero;
              int_type const  m_zero;
  
          public:
              lcast_put_unsigned(const T n_param, CharT* finish) BOOST_NOEXCEPT 
                  : m_value(n_param), m_finish(finish)
                  , m_czero(lcast_char_constants<CharT>::zero), m_zero(Traits::to_int_type(m_czero))
              {
  #ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
                  BOOST_STATIC_ASSERT(!std::numeric_limits<T>::is_signed);
  #endif
              }
  
              CharT* convert() {
  #ifndef BOOST_LEXICAL_CAST_ASSUME_C_LOCALE
                  std::locale loc;
                  if (loc == std::locale::classic()) {
                      return main_convert_loop();
                  }
  
                  typedef std::numpunct<CharT> numpunct;
                  numpunct const& np = BOOST_USE_FACET(numpunct, loc);
                  std::string const grouping = np.grouping();
                  std::string::size_type const grouping_size = grouping.size();
  
                  if (!grouping_size || grouping[0] <= 0) {
                      return main_convert_loop();
                  }
  
  #ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
                  // Check that ulimited group is unreachable:
                  BOOST_STATIC_ASSERT(std::numeric_limits<T>::digits10 < CHAR_MAX);
  #endif
                  CharT const thousands_sep = np.thousands_sep();
                  std::string::size_type group = 0; // current group number
                  char last_grp_size = grouping[0];
                  char left = last_grp_size;
  
                  do {
                      if (left == 0) {
                          ++group;
                          if (group < grouping_size) {
                              char const grp_size = grouping[group];
                              last_grp_size = (grp_size <= 0 ? static_cast<char>(CHAR_MAX) : grp_size);
                          }
  
                          left = last_grp_size;
                          --m_finish;
                          Traits::assign(*m_finish, thousands_sep);
                      }
  
                      --left;
                  } while (main_convert_iteration());
  
                  return m_finish;
  #else
                  return main_convert_loop();
  #endif
              }
  
          private:
              inline bool main_convert_iteration() BOOST_NOEXCEPT {
                  --m_finish;
                  int_type const digit = static_cast<int_type>(m_value % 10U);
                  Traits::assign(*m_finish, Traits::to_char_type(m_zero + digit));
                  m_value /= 10;
                  return !!m_value; // suppressing warnings
              }
  
              inline CharT* main_convert_loop() BOOST_NOEXCEPT {
                  while (main_convert_iteration());
                  return m_finish;
              }
          };
      }
  
      namespace detail // lcast_ret_unsigned
      {
          template <class Traits, class T, class CharT>
          class lcast_ret_unsigned: boost::noncopyable {
              bool m_multiplier_overflowed;
              T m_multiplier;
              T& m_value;
              const CharT* const m_begin;
              const CharT* m_end;
      
          public:
              lcast_ret_unsigned(T& value, const CharT* const begin, const CharT* end) BOOST_NOEXCEPT
                  : m_multiplier_overflowed(false), m_multiplier(1), m_value(value), m_begin(begin), m_end(end)
              {
  #ifndef BOOST_NO_LIMITS_COMPILE_TIME_CONSTANTS
                  BOOST_STATIC_ASSERT(!std::numeric_limits<T>::is_signed);
  
                  // GCC when used with flag -std=c++0x may not have std::numeric_limits
                  // specializations for __int128 and unsigned __int128 types.
                  // Try compilation with -std=gnu++0x or -std=gnu++11.
                  //
                  // http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40856
                  BOOST_STATIC_ASSERT_MSG(std::numeric_limits<T>::is_specialized,
                      "std::numeric_limits are not specialized for integral type passed to boost::lexical_cast"
                  );
  #endif
              }
  
              inline bool convert() {
                  CharT const czero = lcast_char_constants<CharT>::zero;
                  --m_end;
                  m_value = static_cast<T>(0);
  
                  if (m_begin > m_end || *m_end < czero || *m_end >= czero + 10)
                      return false;
                  m_value = static_cast<T>(*m_end - czero);
                  --m_end;
  
  #ifdef BOOST_LEXICAL_CAST_ASSUME_C_LOCALE
                  return main_convert_loop();
  #else
                  std::locale loc;
                  if (loc == std::locale::classic()) {
                      return main_convert_loop();
                  }
  
                  typedef std::numpunct<CharT> numpunct;
                  numpunct const& np = BOOST_USE_FACET(numpunct, loc);
                  std::string const& grouping = np.grouping();
                  std::string::size_type const grouping_size = grouping.size();
  
                  /* According to Programming languages - C++
                   * we MUST check for correct grouping
                   */
                  if (!grouping_size || grouping[0] <= 0) {
                      return main_convert_loop();
                  }
  
                  unsigned char current_grouping = 0;
                  CharT const thousands_sep = np.thousands_sep();
                  char remained = static_cast<char>(grouping[current_grouping] - 1);
  
                  for (;m_end >= m_begin; --m_end)
                  {
                      if (remained) {
                          if (!main_convert_iteration()) {
                              return false;
                          }
                          --remained;
                      } else {
                          if ( !Traits::eq(*m_end, thousands_sep) ) //|| begin == end ) return false;
                          {
                              /*
                               * According to Programming languages - C++
                               * Digit grouping is checked. That is, the positions of discarded
                               * separators is examined for consistency with
                               * use_facet<numpunct<charT> >(loc ).grouping()
                               *
                               * BUT what if there is no separators at all and grouping()
                               * is not empty? Well, we have no extraced separators, so we
                               * won`t check them for consistency. This will allow us to
                               * work with "C" locale from other locales
                               */
                              return main_convert_loop();
                          } else {
                              if (m_begin == m_end) return false;
                              if (current_grouping < grouping_size - 1) ++current_grouping;
                              remained = grouping[current_grouping];
                          }
                      }
                  } /*for*/
  
                  return true;
  #endif
              }
  
          private:
              // Iteration that does not care about grouping/separators and assumes that all 
              // input characters are digits
              inline bool main_convert_iteration() BOOST_NOEXCEPT {
                  CharT const czero = lcast_char_constants<CharT>::zero;
                  T const maxv = (std::numeric_limits<T>::max)();
  
                  m_multiplier_overflowed = m_multiplier_overflowed || (maxv/10 < m_multiplier);
                  m_multiplier = static_cast<T>(m_multiplier * 10);
  
                  T const dig_value = static_cast<T>(*m_end - czero);
                  T const new_sub_value = static_cast<T>(m_multiplier * dig_value);
  
                  // We must correctly handle situations like `000000000000000000000000000001`.
                  // So we take care of overflow only if `dig_value` is not '0'.
                  if (*m_end < czero || *m_end >= czero + 10  // checking for correct digit
                      || (dig_value && (                      // checking for overflow of ... 
                          m_multiplier_overflowed                             // ... multiplier
                          || static_cast<T>(maxv / dig_value) < m_multiplier  // ... subvalue
                          || static_cast<T>(maxv - new_sub_value) < m_value   // ... whole expression
                      ))
                  ) return false;
  
                  m_value = static_cast<T>(m_value + new_sub_value);
                  
                  return true;
              }
  
              bool main_convert_loop() BOOST_NOEXCEPT {
                  for ( ; m_end >= m_begin; --m_end) {
                      if (!main_convert_iteration()) {
                          return false;
                      }
                  }
              
                  return true;
              }
          };
      }
  } // namespace boost
  
  #endif // BOOST_LEXICAL_CAST_DETAIL_LCAST_UNSIGNED_CONVERTERS_HPP
  
  