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 /////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8
 // utf8_codecvt_facet.ipp
 
 // Copyright (c) 2001 Ronald Garcia, Indiana University (garcia@osl.iu.edu)
 // Andrew Lumsdaine, Indiana University (lums@osl.iu.edu).
 // Use, modification and distribution is 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)
 
 // Please see the comments in <boost/detail/utf8_codecvt_facet.hpp> to
 // learn how this file should be used.
 
 #include <boost/detail/utf8_codecvt_facet.hpp>
 
 #include <cstdlib> // for multi-byte converson routines
 #include <cassert>
 
 #include <boost/limits.hpp>
 #include <boost/config.hpp>
 
 // If we don't have wstring, then Unicode support
 // is not available anyway, so we don't need to even
 // compiler this file. This also fixes the problem
 // with mingw, which can compile this file, but will
 // generate link error when building DLL.
 #ifndef BOOST_NO_STD_WSTRING
 
 BOOST_UTF8_BEGIN_NAMESPACE
 
 /////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8
 // implementation for wchar_t
 
 namespace detail {
 
 inline const wchar_t * get_octet1_modifier_table() BOOST_NOEXCEPT
 {
     static const wchar_t octet1_modifier_table[] = {
         0x00, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc
     };
     return octet1_modifier_table;
 }
 
 } // namespace detail
 
 
 BOOST_UTF8_DECL utf8_codecvt_facet::utf8_codecvt_facet(
     std::size_t no_locale_manage
 ) :
     std::codecvt<wchar_t, char, std::mbstate_t>(no_locale_manage)
 {}
 
 BOOST_UTF8_DECL utf8_codecvt_facet::~utf8_codecvt_facet()
 {}
 
 // Translate incoming UTF-8 into UCS-4
 BOOST_UTF8_DECL std::codecvt_base::result utf8_codecvt_facet::do_in(
     std::mbstate_t& /*state*/,
     const char * from,
     const char * from_end,
     const char * & from_next,
     wchar_t * to,
     wchar_t * to_end,
     wchar_t * & to_next
 ) const {
     // Basic algorithm: The first octet determines how many
     // octets total make up the UCS-4 character. The remaining
     // "continuing octets" all begin with "10". To convert, subtract
     // the amount that specifies the number of octets from the first
     // octet. Subtract 0x80 (1000 0000) from each continuing octet,
     // then mash the whole lot together. Note that each continuing
     // octet only uses 6 bits as unique values, so only shift by
     // multiples of 6 to combine.
     const wchar_t * const octet1_modifier_table = detail::get_octet1_modifier_table();
     while (from != from_end && to != to_end) {
 
         // Error checking on the first octet
         if (invalid_leading_octet(*from)) {
             from_next = from;
             to_next = to;
             return std::codecvt_base::error;
         }
 
         // The first octet is adjusted by a value dependent upon
         // the number of "continuing octets" encoding the character
         const int cont_octet_count = get_cont_octet_count(*from);
 
         // The unsigned char conversion is necessary in case char is
         // signed (I learned this the hard way)
         wchar_t ucs_result =
             (unsigned char)(*from++) - octet1_modifier_table[cont_octet_count];
 
         // Invariants:
         //   1) At the start of the loop, 'i' continuing characters have been
         //      processed
         //   2) *from points to the next continuing character to be processed.
         int i = 0;
         while (i != cont_octet_count && from != from_end) {
 
             // Error checking on continuing characters
             if (invalid_continuing_octet(*from)) {
                 from_next = from;
                 to_next = to;
                 return std::codecvt_base::error;
             }
 
             ucs_result *= (1 << 6);
 
             // each continuing character has an extra (10xxxxxx)b attached to
             // it that must be removed.
             ucs_result += (unsigned char)(*from++) - 0x80;
             ++i;
         }
 
         // If the buffer ends with an incomplete unicode character...
         if (from == from_end && i != cont_octet_count) {
             // rewind "from" to before the current character translation
             from_next = from - (i + 1);
             to_next = to;
             return std::codecvt_base::partial;
         }
         *to++ = ucs_result;
     }
     from_next = from;
     to_next = to;
 
     // Were we done converting or did we run out of destination space?
     if (from == from_end)
         return std::codecvt_base::ok;
     else
         return std::codecvt_base::partial;
 }
 
 BOOST_UTF8_DECL std::codecvt_base::result utf8_codecvt_facet::do_out(
     std::mbstate_t& /*state*/,
     const wchar_t * from,
     const wchar_t * from_end,
     const wchar_t * & from_next,
     char * to,
     char * to_end,
     char * & to_next
 ) const
 {
     const wchar_t * const octet1_modifier_table = detail::get_octet1_modifier_table();
     wchar_t max_wchar = (std::numeric_limits<wchar_t>::max)();
     while (from != from_end && to != to_end) {
 
         // Check for invalid UCS-4 character
         if (*from  > max_wchar) {
             from_next = from;
             to_next = to;
             return std::codecvt_base::error;
         }
 
         int cont_octet_count = get_cont_octet_out_count(*from);
 
         // RG - comment this formula better
         int shift_exponent = cont_octet_count * 6;
 
         // Process the first character
         *to++ = static_cast<char>(octet1_modifier_table[cont_octet_count] +
             (unsigned char)(*from / (1 << shift_exponent)));
 
         // Process the continuation characters
         // Invariants: At the start of the loop:
         //   1) 'i' continuing octets have been generated
         //   2) '*to' points to the next location to place an octet
         //   3) shift_exponent is 6 more than needed for the next octet
         int i = 0;
         while (i != cont_octet_count && to != to_end) {
             shift_exponent -= 6;
             *to++ = static_cast<char>(0x80 + ((*from / (1 << shift_exponent)) % (1 << 6)));
             ++i;
         }
         // If we filled up the out buffer before encoding the character
         if (to == to_end && i != cont_octet_count) {
             from_next = from;
             to_next = to - (i + 1);
             return std::codecvt_base::partial;
         }
         ++from;
     }
     from_next = from;
     to_next = to;
 
     // Were we done or did we run out of destination space
     if (from == from_end)
         return std::codecvt_base::ok;
     else
         return std::codecvt_base::partial;
 }
 
 // How many char objects can I process to get <= max_limit
 // wchar_t objects?
 BOOST_UTF8_DECL int utf8_codecvt_facet::do_length(
     std::mbstate_t &,
     const char * from,
     const char * from_end,
     std::size_t max_limit
 ) const
 #if BOOST_WORKAROUND(__IBMCPP__, BOOST_TESTED_AT(600))
         throw()
 #endif
 {
     const char * from_next = from;
     for (std::size_t char_count = 0u; char_count < max_limit && from_next < from_end; ++char_count) {
         unsigned int octet_count = get_octet_count(*from_next);
         // The buffer may represent incomplete characters, so terminate early if one is found
         if (octet_count > static_cast<std::size_t>(from_end - from_next))
             break;
         from_next += octet_count;
     }
 
     return static_cast<int>(from_next - from);
 }
 
 BOOST_UTF8_DECL unsigned int utf8_codecvt_facet::get_octet_count(
     unsigned char lead_octet
 ) {
     // if the 0-bit (MSB) is 0, then 1 character
     if (lead_octet <= 0x7f) return 1;
 
     // Otherwise the count number of consecutive 1 bits starting at MSB
 //    assert(0xc0 <= lead_octet && lead_octet <= 0xfd);
 
     if (0xc0 <= lead_octet && lead_octet <= 0xdf) return 2;
     else if (0xe0 <= lead_octet && lead_octet <= 0xef) return 3;
     else if (0xf0 <= lead_octet && lead_octet <= 0xf7) return 4;
     else if (0xf8 <= lead_octet && lead_octet <= 0xfb) return 5;
     else return 6;
 }
 
 namespace detail {
 
 template<std::size_t s>
 inline int get_cont_octet_out_count_impl(wchar_t word) {
     if (word < 0x80) {
         return 0;
     }
     if (word < 0x800) {
         return 1;
     }
     return 2;
 }
 
 template<>
 inline int get_cont_octet_out_count_impl<4>(wchar_t word) {
     if (word < 0x80) {
         return 0;
     }
     if (word < 0x800) {
         return 1;
     }
 
     // Note that the following code will generate warnings on some platforms
     // where wchar_t is defined as UCS2.  The warnings are superfluous as the
     // specialization is never instantitiated with such compilers, but this
     // can cause problems if warnings are being treated as errors, so we guard
     // against that. Including <boost/detail/utf8_codecvt_facet.hpp> as we do
     // should be enough to get WCHAR_MAX defined.
 #if !defined(WCHAR_MAX)
 #   error WCHAR_MAX not defined!
 #endif
     // cope with VC++ 7.1 or earlier having invalid WCHAR_MAX
 #if defined(_MSC_VER) && _MSC_VER <= 1310 // 7.1 or earlier
     return 2;
 #elif WCHAR_MAX > 0x10000
 
     if (word < 0x10000) {
         return 2;
     }
     if (word < 0x200000) {
         return 3;
     }
     if (word < 0x4000000) {
         return 4;
     }
     return 5;
 
 #else
     return 2;
 #endif
 }
 
 } // namespace detail
 
 // How many "continuing octets" will be needed for this word
 // ==   total octets - 1.
 BOOST_UTF8_DECL int utf8_codecvt_facet::get_cont_octet_out_count(
     wchar_t word
 ) {
     return detail::get_cont_octet_out_count_impl<sizeof(wchar_t)>(word);
 }
 
 BOOST_UTF8_END_NAMESPACE
 
 #endif

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