generic_codecvt.hpp

//
// Copyright (c) 2015 Artyom Beilis (Tonkikh)
//
// Distributed under the Boost Software License, Version 1.0.
// https://www.boost.org/LICENSE_1_0.txt

#ifndef BOOST_LOCALE_GENERIC_CODECVT_HPP
#define BOOST_LOCALE_GENERIC_CODECVT_HPP

#include <boost/locale/utf.hpp>
#include <boost/cstdint.hpp>
#include <locale>

namespace boost { namespace locale {

#ifndef BOOST_LOCALE_DOXYGEN
    //
    // Make sure that mbstate can keep 16 bit of UTF-16 sequence
    //
    static_assert(sizeof(std::mbstate_t) >= 2, "std::mbstate_t is to small");
#endif

#if defined(_MSC_VER) && _MSC_VER < 1700
// up to MSVC 11 (2012) do_length is non-standard it counts wide characters instead of narrow and does not change
// mbstate
#    define BOOST_LOCALE_DO_LENGTH_MBSTATE_CONST
#endif

    class generic_codecvt_base {
    public:
        enum initial_convertion_state {
            to_unicode_state,  
            from_unicode_state 
        };
    };

    template<typename CharType, typename CodecvtImpl, int CharSize = sizeof(CharType)>
    class generic_codecvt;

    template<typename CharType, typename CodecvtImpl>
    class generic_codecvt<CharType, CodecvtImpl, 2> : public std::codecvt<CharType, char, std::mbstate_t>,
                                                      public generic_codecvt_base {
    public:
        typedef CharType uchar;

        generic_codecvt(size_t refs = 0) : std::codecvt<CharType, char, std::mbstate_t>(refs) {}
        const CodecvtImpl& implementation() const { return *static_cast<const CodecvtImpl*>(this); }

    protected:
        std::codecvt_base::result do_unshift(std::mbstate_t& s, char* from, char* /*to*/, char*& next) const override
        {
            boost::uint16_t& state = *reinterpret_cast<boost::uint16_t*>(&s);
            if(state != 0)
                return std::codecvt_base::error;
            next = from;
            return std::codecvt_base::ok;
        }
        int do_encoding() const noexcept override { return 0; }
        int do_max_length() const noexcept override { return implementation().max_encoding_length(); }
        bool do_always_noconv() const noexcept override { return false; }

        int do_length(
#ifdef BOOST_LOCALE_DO_LENGTH_MBSTATE_CONST
          const
#endif
          std::mbstate_t& std_state,
          const char* from,
          const char* from_end,
          size_t max) const override
        {
#ifndef BOOST_LOCALE_DO_LENGTH_MBSTATE_CONST
            const char* save_from = from;
            boost::uint16_t& state = *reinterpret_cast<boost::uint16_t*>(&std_state);
#else
            const size_t start_max = max;
            boost::uint16_t state = *reinterpret_cast<const boost::uint16_t*>(&std_state);
#endif

            typename CodecvtImpl::state_type cvt_state =
              implementation().initial_state(generic_codecvt_base::to_unicode_state);
            while(max > 0 && from < from_end) {
                const char* prev_from = from;
                boost::uint32_t ch = implementation().to_unicode(cvt_state, from, from_end);
                if(ch == boost::locale::utf::incomplete || ch == boost::locale::utf::illegal) {
                    from = prev_from;
                    break;
                }
                max--;
                if(ch > 0xFFFF) {
                    if(state == 0) {
                        from = prev_from;
                        state = 1;
                    } else {
                        state = 0;
                    }
                }
            }
#ifndef BOOST_LOCALE_DO_LENGTH_MBSTATE_CONST
            return static_cast<int>(from - save_from);
#else
            return static_cast<int>(start_max - max);
#endif
        }

        std::codecvt_base::result do_in(std::mbstate_t& std_state,
                                        const char* from,
                                        const char* from_end,
                                        const char*& from_next,
                                        uchar* to,
                                        uchar* to_end,
                                        uchar*& to_next) const override
        {
            std::codecvt_base::result r = std::codecvt_base::ok;

            // mbstate_t is POD type and should be initialized to 0 (i.a. state = stateT())
            // according to standard. We use it to keep a flag 0/1 for surrogate pair writing
            //
            // if 0 no code above >0xFFFF observed, of 1 a code above 0xFFFF observed
            // and first pair is written, but no input consumed
            boost::uint16_t& state = *reinterpret_cast<boost::uint16_t*>(&std_state);
            typename CodecvtImpl::state_type cvt_state =
              implementation().initial_state(generic_codecvt_base::to_unicode_state);
            while(to < to_end && from < from_end) {
                const char* from_saved = from;

                uint32_t ch = implementation().to_unicode(cvt_state, from, from_end);

                if(ch == boost::locale::utf::illegal) {
                    from = from_saved;
                    r = std::codecvt_base::error;
                    break;
                }
                if(ch == boost::locale::utf::incomplete) {
                    from = from_saved;
                    r = std::codecvt_base::partial;
                    break;
                }
                // Normal codepoints go directly to stream
                if(ch <= 0xFFFF) {
                    *to++ = static_cast<uchar>(ch);
                } else {
                    // For other codepoints we do the following
                    //
                    // 1. We can't consume our input as we may find ourselves
                    //    in state where all input consumed but not all output written,i.e. only
                    //    1st pair is written
                    // 2. We only write first pair and mark this in the state, we also revert back
                    //    the from pointer in order to make sure this codepoint would be read
                    //    once again and then we would consume our input together with writing
                    //    second surrogate pair
                    ch -= 0x10000;
                    boost::uint16_t w1 = static_cast<boost::uint16_t>(0xD800 | (ch >> 10));
                    boost::uint16_t w2 = static_cast<boost::uint16_t>(0xDC00 | (ch & 0x3FF));
                    if(state == 0) {
                        from = from_saved;
                        *to++ = w1;
                        state = 1;
                    } else {
                        *to++ = w2;
                        state = 0;
                    }
                }
            }
            from_next = from;
            to_next = to;
            if(r == std::codecvt_base::ok && (from != from_end || state != 0))
                r = std::codecvt_base::partial;
            return r;
        }

        std::codecvt_base::result do_out(std::mbstate_t& std_state,
                                         const uchar* from,
                                         const uchar* from_end,
                                         const uchar*& from_next,
                                         char* to,
                                         char* to_end,
                                         char*& to_next) const override
        {
            std::codecvt_base::result r = std::codecvt_base::ok;
            // mbstate_t is POD type and should be initialized to 0 (i.a. state = stateT())
            // according to standard. We assume that sizeof(mbstate_t) >=2 in order
            // to be able to store first observed surrogate pair
            //
            // State: state!=0 - a first surrogate pair was observed (state = first pair),
            // we expect the second one to come and then zero the state
            boost::uint16_t& state = *reinterpret_cast<boost::uint16_t*>(&std_state);
            typename CodecvtImpl::state_type cvt_state =
              implementation().initial_state(generic_codecvt_base::from_unicode_state);
            while(to < to_end && from < from_end) {
                boost::uint32_t ch = 0;
                if(state != 0) {
                    // if the state indicates that 1st surrogate pair was written
                    // we should make sure that the second one that comes is actually
                    // second surrogate
                    boost::uint16_t w1 = state;
                    boost::uint16_t w2 = *from;
                    // we don't forward from as writing may fail to incomplete or
                    // partial conversion
                    if(0xDC00 <= w2 && w2 <= 0xDFFF) {
                        boost::uint16_t vh = w1 - 0xD800;
                        boost::uint16_t vl = w2 - 0xDC00;
                        ch = ((uint32_t(vh) << 10) | vl) + 0x10000;
                    } else {
                        // Invalid surrogate
                        r = std::codecvt_base::error;
                        break;
                    }
                } else {
                    ch = *from;
                    if(0xD800 <= ch && ch <= 0xDBFF) {
                        // if this is a first surrogate pair we put
                        // it into the state and consume it, note we don't
                        // go forward as it should be illegal so we increase
                        // the from pointer manually
                        state = static_cast<uint16_t>(ch);
                        from++;
                        continue;
                    } else if(0xDC00 <= ch && ch <= 0xDFFF) {
                        // if we observe second surrogate pair and
                        // first only may be expected we should break from the loop with error
                        // as it is illegal input
                        r = std::codecvt_base::error;
                        break;
                    }
                }
                if(!boost::locale::utf::is_valid_codepoint(ch)) {
                    r = std::codecvt_base::error;
                    break;
                }
                boost::uint32_t len = implementation().from_unicode(cvt_state, ch, to, to_end);
                if(len == boost::locale::utf::incomplete) {
                    r = std::codecvt_base::partial;
                    break;
                } else if(len == boost::locale::utf::illegal) {
                    r = std::codecvt_base::error;
                    break;
                } else
                    to += len;
                state = 0;
                from++;
            }
            from_next = from;
            to_next = to;
            if(r == std::codecvt_base::ok && (from != from_end || state != 0))
                r = std::codecvt_base::partial;
            return r;
        }
    };

    template<typename CharType, typename CodecvtImpl>
    class generic_codecvt<CharType, CodecvtImpl, 4> : public std::codecvt<CharType, char, std::mbstate_t>,
                                                      public generic_codecvt_base {
    public:
        typedef CharType uchar;

        generic_codecvt(size_t refs = 0) : std::codecvt<CharType, char, std::mbstate_t>(refs) {}

        const CodecvtImpl& implementation() const { return *static_cast<const CodecvtImpl*>(this); }

    protected:
        std::codecvt_base::result
        do_unshift(std::mbstate_t& /*s*/, char* from, char* /*to*/, char*& next) const override
        {
            next = from;
            return std::codecvt_base::ok;
        }
        int do_encoding() const noexcept override { return 0; }
        int do_max_length() const noexcept override { return implementation().max_encoding_length(); }
        bool do_always_noconv() const noexcept override { return false; }

        int do_length(
#ifdef BOOST_LOCALE_DO_LENGTH_MBSTATE_CONST
          const
#endif
          std::mbstate_t& /*state*/,
          const char* from,
          const char* from_end,
          size_t max) const override
        {
#ifndef BOOST_LOCALE_DO_LENGTH_MBSTATE_CONST
            const char* start_from = from;
#else
            const size_t start_max = max;
#endif
            typename CodecvtImpl::state_type cvt_state =
              implementation().initial_state(generic_codecvt_base::to_unicode_state);
            while(max > 0 && from < from_end) {
                const char* save_from = from;
                boost::uint32_t ch = implementation().to_unicode(cvt_state, from, from_end);
                if(ch == boost::locale::utf::incomplete || ch == boost::locale::utf::illegal) {
                    from = save_from;
                    break;
                }
                max--;
            }

#ifndef BOOST_LOCALE_DO_LENGTH_MBSTATE_CONST
            return static_cast<int>(from - start_from);
#else
            return static_cast<int>(start_max - max);
#endif
        }

        std::codecvt_base::result do_in(std::mbstate_t& /*state*/,
                                        const char* from,
                                        const char* from_end,
                                        const char*& from_next,
                                        uchar* to,
                                        uchar* to_end,
                                        uchar*& to_next) const override
        {
            std::codecvt_base::result r = std::codecvt_base::ok;

            // mbstate_t is POD type and should be initialized to 0 (i.a. state = stateT())
            // according to standard. We use it to keep a flag 0/1 for surrogate pair writing
            //
            // if 0 no code above >0xFFFF observed, of 1 a code above 0xFFFF observed
            // and first pair is written, but no input consumed
            auto cvt_state = implementation().initial_state(generic_codecvt_base::to_unicode_state);
            while(to < to_end && from < from_end) {
                const char* from_saved = from;

                uint32_t ch = implementation().to_unicode(cvt_state, from, from_end);

                if(ch == boost::locale::utf::illegal) {
                    r = std::codecvt_base::error;
                    from = from_saved;
                    break;
                }
                if(ch == boost::locale::utf::incomplete) {
                    r = std::codecvt_base::partial;
                    from = from_saved;
                    break;
                }
                *to++ = ch;
            }
            from_next = from;
            to_next = to;
            if(r == std::codecvt_base::ok && from != from_end)
                r = std::codecvt_base::partial;
            return r;
        }

        std::codecvt_base::result do_out(std::mbstate_t& /*std_state*/,
                                         const uchar* from,
                                         const uchar* from_end,
                                         const uchar*& from_next,
                                         char* to,
                                         char* to_end,
                                         char*& to_next) const override
        {
            std::codecvt_base::result r = std::codecvt_base::ok;
            auto cvt_state = implementation().initial_state(generic_codecvt_base::from_unicode_state);
            while(to < to_end && from < from_end) {
                boost::uint32_t ch = 0;
                ch = *from;
                if(!boost::locale::utf::is_valid_codepoint(ch)) {
                    r = std::codecvt_base::error;
                    break;
                }
                boost::uint32_t len = implementation().from_unicode(cvt_state, ch, to, to_end);
                if(len == boost::locale::utf::incomplete) {
                    r = std::codecvt_base::partial;
                    break;
                } else if(len == boost::locale::utf::illegal) {
                    r = std::codecvt_base::error;
                    break;
                }
                to += len;
                from++;
            }
            from_next = from;
            to_next = to;
            if(r == std::codecvt_base::ok && from != from_end)
                r = std::codecvt_base::partial;
            return r;
        }
    };

    template<typename CharType, typename CodecvtImpl>
    class generic_codecvt<CharType, CodecvtImpl, 1> : public std::codecvt<CharType, char, std::mbstate_t>,
                                                      public generic_codecvt_base {
    public:
        typedef CharType uchar;

        const CodecvtImpl& implementation() const { return *static_cast<const CodecvtImpl*>(this); }

        generic_codecvt(size_t refs = 0) : std::codecvt<char, char, std::mbstate_t>(refs) {}
    };

}} // namespace boost::locale

#endif