Index: libcxx/include/codecvt
===================================================================
--- libcxx/include/codecvt
+++ libcxx/include/codecvt
@@ -73,9 +73,10 @@
 // codecvt_utf8
 
 template <class _Elem> class __codecvt_utf8;
+template <class _Elem, size_t _ElemSize> class __codecvt_utf8_imp;
 
 template <>
-class _LIBCPP_TYPE_VIS __codecvt_utf8<wchar_t>
+class _LIBCPP_TYPE_VIS __codecvt_utf8_imp<wchar_t, 2>
     : public codecvt<wchar_t, char, mbstate_t>
 {
     unsigned long _Maxcode_;
@@ -86,7 +87,42 @@
     typedef mbstate_t state_type;
 
     _LIBCPP_INLINE_VISIBILITY
-    explicit __codecvt_utf8(size_t __refs, unsigned long _Maxcode,
+    explicit __codecvt_utf8_imp(size_t __refs, unsigned long _Maxcode,
+                            codecvt_mode _Mode)
+        : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
+          _Mode_(_Mode) {}
+protected:
+    virtual result
+        do_out(state_type& __st,
+               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
+    virtual result
+        do_in(state_type& __st,
+              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
+    virtual result
+        do_unshift(state_type& __st,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
+    virtual int do_encoding() const throw();
+    virtual bool do_always_noconv() const throw();
+    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
+                          size_t __mx) const;
+    virtual int do_max_length() const throw();
+};
+
+template <>
+class _LIBCPP_TYPE_VIS __codecvt_utf8_imp<wchar_t, 4>
+    : public codecvt<wchar_t, char, mbstate_t>
+{
+    unsigned long _Maxcode_;
+    codecvt_mode _Mode_;
+public:
+    typedef wchar_t   intern_type;
+    typedef char      extern_type;
+    typedef mbstate_t state_type;
+
+    _LIBCPP_INLINE_VISIBILITY
+    explicit __codecvt_utf8_imp(size_t __refs, unsigned long _Maxcode,
                             codecvt_mode _Mode)
         : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
           _Mode_(_Mode) {}
@@ -110,6 +146,19 @@
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
+template <>
+class _LIBCPP_TYPE_VIS __codecvt_utf8<wchar_t>
+    : public __codecvt_utf8_imp<wchar_t, sizeof(wchar_t)>
+{
+public:
+    _LIBCPP_INLINE_VISIBILITY
+    explicit __codecvt_utf8(size_t __refs, unsigned long _Maxcode, codecvt_mode _Mode)
+        : __codecvt_utf8_imp<wchar_t, sizeof(wchar_t)>(__refs, _Maxcode, _Mode) {}
+
+    _LIBCPP_INLINE_VISIBILITY
+    ~__codecvt_utf8() {}
+};
+
 template <>
 class _LIBCPP_TYPE_VIS __codecvt_utf8<char16_t>
     : public codecvt<char16_t, char, mbstate_t>
@@ -202,9 +251,10 @@
 // codecvt_utf16
 
 template <class _Elem, bool _LittleEndian> class __codecvt_utf16;
+template <class _Elem, bool _LittleEndian, size_t _ElemSize> class __codecvt_utf16_imp;
 
 template <>
-class _LIBCPP_TYPE_VIS __codecvt_utf16<wchar_t, false>
+class _LIBCPP_TYPE_VIS __codecvt_utf16_imp<wchar_t, false, 2>
     : public codecvt<wchar_t, char, mbstate_t>
 {
     unsigned long _Maxcode_;
@@ -215,7 +265,7 @@
     typedef mbstate_t state_type;
 
     _LIBCPP_INLINE_VISIBILITY
-    explicit __codecvt_utf16(size_t __refs, unsigned long _Maxcode,
+    explicit __codecvt_utf16_imp(size_t __refs, unsigned long _Maxcode,
                             codecvt_mode _Mode)
         : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
           _Mode_(_Mode) {}
@@ -239,7 +289,7 @@
 };
 
 template <>
-class _LIBCPP_TYPE_VIS __codecvt_utf16<wchar_t, true>
+class _LIBCPP_TYPE_VIS __codecvt_utf16_imp<wchar_t, true, 2>
     : public codecvt<wchar_t, char, mbstate_t>
 {
     unsigned long _Maxcode_;
@@ -250,7 +300,77 @@
     typedef mbstate_t state_type;
 
     _LIBCPP_INLINE_VISIBILITY
-    explicit __codecvt_utf16(size_t __refs, unsigned long _Maxcode,
+    explicit __codecvt_utf16_imp(size_t __refs, unsigned long _Maxcode,
+                            codecvt_mode _Mode)
+        : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
+          _Mode_(_Mode) {}
+protected:
+    virtual result
+        do_out(state_type& __st,
+               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
+    virtual result
+        do_in(state_type& __st,
+              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
+    virtual result
+        do_unshift(state_type& __st,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
+    virtual int do_encoding() const throw();
+    virtual bool do_always_noconv() const throw();
+    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
+                          size_t __mx) const;
+    virtual int do_max_length() const throw();
+};
+
+template <>
+class _LIBCPP_TYPE_VIS __codecvt_utf16_imp<wchar_t, false, 4>
+    : public codecvt<wchar_t, char, mbstate_t>
+{
+    unsigned long _Maxcode_;
+    codecvt_mode _Mode_;
+public:
+    typedef wchar_t   intern_type;
+    typedef char      extern_type;
+    typedef mbstate_t state_type;
+
+    _LIBCPP_INLINE_VISIBILITY
+    explicit __codecvt_utf16_imp(size_t __refs, unsigned long _Maxcode,
+                            codecvt_mode _Mode)
+        : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
+          _Mode_(_Mode) {}
+protected:
+    virtual result
+        do_out(state_type& __st,
+               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
+    virtual result
+        do_in(state_type& __st,
+              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
+    virtual result
+        do_unshift(state_type& __st,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
+    virtual int do_encoding() const throw();
+    virtual bool do_always_noconv() const throw();
+    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
+                          size_t __mx) const;
+    virtual int do_max_length() const throw();
+};
+
+template <>
+class _LIBCPP_TYPE_VIS __codecvt_utf16_imp<wchar_t, true, 4>
+    : public codecvt<wchar_t, char, mbstate_t>
+{
+    unsigned long _Maxcode_;
+    codecvt_mode _Mode_;
+public:
+    typedef wchar_t   intern_type;
+    typedef char      extern_type;
+    typedef mbstate_t state_type;
+
+    _LIBCPP_INLINE_VISIBILITY 
+    explicit __codecvt_utf16_imp(size_t __refs, unsigned long _Maxcode,
                             codecvt_mode _Mode)
         : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
           _Mode_(_Mode) {}
@@ -274,6 +394,36 @@
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
+template <>
+class _LIBCPP_TYPE_VIS __codecvt_utf16<wchar_t, false>
+    : public __codecvt_utf16_imp<wchar_t, false, sizeof(wchar_t)>
+{
+public:
+    _LIBCPP_INLINE_VISIBILITY
+    explicit __codecvt_utf16(size_t __refs, unsigned long _Maxcode, codecvt_mode
+ _Mode)
+        : __codecvt_utf16_imp<wchar_t, false, sizeof(wchar_t)>(__refs, _Maxcode, _Mode)
+ {}
+
+    _LIBCPP_INLINE_VISIBILITY
+    ~__codecvt_utf16() {}
+};
+
+template <>
+class _LIBCPP_TYPE_VIS __codecvt_utf16<wchar_t, true>
+    : public __codecvt_utf16_imp<wchar_t, true, sizeof(wchar_t)>
+{
+public:
+    _LIBCPP_INLINE_VISIBILITY
+    explicit __codecvt_utf16(size_t __refs, unsigned long _Maxcode, codecvt_mode
+ _Mode)
+        : __codecvt_utf16_imp<wchar_t, true, sizeof(wchar_t)>(__refs, _Maxcode, _Mode)
+ {}
+
+    _LIBCPP_INLINE_VISIBILITY
+    ~__codecvt_utf16() {}
+};
+
 template <>
 class _LIBCPP_TYPE_VIS __codecvt_utf16<char16_t, false>
     : public codecvt<char16_t, char, mbstate_t>
@@ -442,9 +592,10 @@
 // codecvt_utf8_utf16
 
 template <class _Elem> class __codecvt_utf8_utf16;
+template <class _Elem, size_t _ElemSize> class __codecvt_utf8_utf16_imp;
 
 template <>
-class _LIBCPP_TYPE_VIS __codecvt_utf8_utf16<wchar_t>
+class _LIBCPP_TYPE_VIS __codecvt_utf8_utf16_imp<wchar_t, 2>
     : public codecvt<wchar_t, char, mbstate_t>
 {
     unsigned long _Maxcode_;
@@ -455,7 +606,42 @@
     typedef mbstate_t state_type;
 
     _LIBCPP_INLINE_VISIBILITY
-    explicit __codecvt_utf8_utf16(size_t __refs, unsigned long _Maxcode,
+    explicit __codecvt_utf8_utf16_imp(size_t __refs, unsigned long _Maxcode,
+                            codecvt_mode _Mode)
+        : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
+          _Mode_(_Mode) {}
+protected:
+    virtual result
+        do_out(state_type& __st,
+               const intern_type* __frm, const intern_type* __frm_end, const intern_type*& __frm_nxt,
+               extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
+    virtual result
+        do_in(state_type& __st,
+              const extern_type* __frm, const extern_type* __frm_end, const extern_type*& __frm_nxt,
+              intern_type* __to, intern_type* __to_end, intern_type*& __to_nxt) const;
+    virtual result
+        do_unshift(state_type& __st,
+                   extern_type* __to, extern_type* __to_end, extern_type*& __to_nxt) const;
+    virtual int do_encoding() const throw();
+    virtual bool do_always_noconv() const throw();
+    virtual int do_length(state_type&, const extern_type* __frm, const extern_type* __end,
+                          size_t __mx) const;
+    virtual int do_max_length() const throw();
+};
+
+template <>
+class _LIBCPP_TYPE_VIS __codecvt_utf8_utf16_imp<wchar_t, 4>
+    : public codecvt<wchar_t, char, mbstate_t>
+{
+    unsigned long _Maxcode_;
+    codecvt_mode _Mode_;
+public:
+    typedef wchar_t   intern_type;
+    typedef char      extern_type;
+    typedef mbstate_t state_type;
+
+    _LIBCPP_INLINE_VISIBILITY
+    explicit __codecvt_utf8_utf16_imp(size_t __refs, unsigned long _Maxcode,
                             codecvt_mode _Mode)
         : codecvt<wchar_t, char, mbstate_t>(__refs), _Maxcode_(_Maxcode),
           _Mode_(_Mode) {}
@@ -479,6 +665,19 @@
 };
 
 _LIBCPP_SUPPRESS_DEPRECATED_PUSH
+template <>
+class _LIBCPP_TYPE_VIS __codecvt_utf8_utf16<wchar_t>
+    : public __codecvt_utf8_utf16_imp<wchar_t, sizeof(wchar_t)>
+{
+public:
+    _LIBCPP_INLINE_VISIBILITY
+    explicit __codecvt_utf8_utf16(size_t __refs, unsigned long _Maxcode, codecvt_mode _Mode)
+        : __codecvt_utf8_utf16_imp<wchar_t, sizeof(wchar_t)>(__refs, _Maxcode, _Mode) {}
+
+    _LIBCPP_INLINE_VISIBILITY
+    ~__codecvt_utf8_utf16() {}
+};
+
 template <>
 class _LIBCPP_TYPE_VIS __codecvt_utf8_utf16<char32_t>
     : public codecvt<char32_t, char, mbstate_t>
Index: libcxx/src/locale.cpp
===================================================================
--- libcxx/src/locale.cpp
+++ libcxx/src/locale.cpp
@@ -3434,65 +3434,121 @@
 
 #endif
 
-// __codecvt_utf8<wchar_t>
+// __codecvt_utf8_imp<wchar_t, 2>
 
-__codecvt_utf8<wchar_t>::result
-__codecvt_utf8<wchar_t>::do_out(state_type&,
+__codecvt_utf8_imp<wchar_t, 2>::result
+__codecvt_utf8_imp<wchar_t, 2>::do_out(state_type&,
     const intern_type* frm, const intern_type* frm_end, const intern_type*& frm_nxt,
     extern_type* to, extern_type* to_end, extern_type*& to_nxt) const
 {
-#if defined(_LIBCPP_SHORT_WCHAR)
     const uint16_t* _frm = reinterpret_cast<const uint16_t*>(frm);
     const uint16_t* _frm_end = reinterpret_cast<const uint16_t*>(frm_end);
     const uint16_t* _frm_nxt = _frm;
-#else
-    const uint32_t* _frm = reinterpret_cast<const uint32_t*>(frm);
-    const uint32_t* _frm_end = reinterpret_cast<const uint32_t*>(frm_end);
-    const uint32_t* _frm_nxt = _frm;
-#endif
     uint8_t* _to = reinterpret_cast<uint8_t*>(to);
     uint8_t* _to_end = reinterpret_cast<uint8_t*>(to_end);
     uint8_t* _to_nxt = _to;
-#if defined(_LIBCPP_SHORT_WCHAR)
     result r = ucs2_to_utf8(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
                             _Maxcode_, _Mode_);
-#else
-    result r = ucs4_to_utf8(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
-                            _Maxcode_, _Mode_);
-#endif
     frm_nxt = frm + (_frm_nxt - _frm);
     to_nxt = to + (_to_nxt - _to);
     return r;
 }
 
-__codecvt_utf8<wchar_t>::result
-__codecvt_utf8<wchar_t>::do_in(state_type&,
+__codecvt_utf8_imp<wchar_t, 2>::result
+__codecvt_utf8_imp<wchar_t, 2>::do_in(state_type&,
     const extern_type* frm, const extern_type* frm_end, const extern_type*& frm_nxt,
     intern_type* to, intern_type* to_end, intern_type*& to_nxt) const
 {
     const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
     const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
     const uint8_t* _frm_nxt = _frm;
-#if defined(_LIBCPP_SHORT_WCHAR)
     uint16_t* _to = reinterpret_cast<uint16_t*>(to);
     uint16_t* _to_end = reinterpret_cast<uint16_t*>(to_end);
     uint16_t* _to_nxt = _to;
     result r = utf8_to_ucs2(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
                             _Maxcode_, _Mode_);
-#else
+    frm_nxt = frm + (_frm_nxt - _frm);
+    to_nxt = to + (_to_nxt - _to);
+    return r;
+}
+
+__codecvt_utf8_imp<wchar_t, 2>::result
+__codecvt_utf8_imp<wchar_t, 2>::do_unshift(state_type&,
+    extern_type* to, extern_type*, extern_type*& to_nxt) const
+{
+    to_nxt = to;
+    return noconv;
+}
+
+int
+__codecvt_utf8_imp<wchar_t, 2>::do_encoding() const  noexcept
+{
+    return 0;
+}
+
+bool
+__codecvt_utf8_imp<wchar_t, 2>::do_always_noconv() const  noexcept
+{
+    return false;
+}
+
+int
+__codecvt_utf8_imp<wchar_t, 2>::do_length(state_type&,
+    const extern_type* frm, const extern_type* frm_end, size_t mx) const
+{
+    const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
+    const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
+    return utf8_to_ucs2_length(_frm, _frm_end, mx, _Maxcode_, _Mode_);
+}
+
+int
+__codecvt_utf8_imp<wchar_t, 2>::do_max_length() const  noexcept
+{
+    if (_Mode_ & consume_header)
+        return 6;
+    return 3;
+}
+
+// __codecvt_utf8_imp<wchar_t, 4>
+
+__codecvt_utf8_imp<wchar_t, 4>::result
+__codecvt_utf8_imp<wchar_t, 4>::do_out(state_type&,
+    const intern_type* frm, const intern_type* frm_end, const intern_type*& frm_nxt,
+    extern_type* to, extern_type* to_end, extern_type*& to_nxt) const
+{
+    const uint32_t* _frm = reinterpret_cast<const uint32_t*>(frm);
+    const uint32_t* _frm_end = reinterpret_cast<const uint32_t*>(frm_end);
+    const uint32_t* _frm_nxt = _frm;
+    uint8_t* _to = reinterpret_cast<uint8_t*>(to);
+    uint8_t* _to_end = reinterpret_cast<uint8_t*>(to_end);
+    uint8_t* _to_nxt = _to;
+    result r = ucs4_to_utf8(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
+                            _Maxcode_, _Mode_);
+    frm_nxt = frm + (_frm_nxt - _frm);
+    to_nxt = to + (_to_nxt - _to);
+    return r;
+}
+
+__codecvt_utf8_imp<wchar_t, 4>::result
+__codecvt_utf8_imp<wchar_t, 4>::do_in(state_type&,
+    const extern_type* frm, const extern_type* frm_end, const extern_type*& frm_nxt,
+    intern_type* to, intern_type* to_end, intern_type*& to_nxt) const
+{
+    const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
+    const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
+    const uint8_t* _frm_nxt = _frm;
     uint32_t* _to = reinterpret_cast<uint32_t*>(to);
     uint32_t* _to_end = reinterpret_cast<uint32_t*>(to_end);
     uint32_t* _to_nxt = _to;
     result r = utf8_to_ucs4(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
                             _Maxcode_, _Mode_);
-#endif
     frm_nxt = frm + (_frm_nxt - _frm);
     to_nxt = to + (_to_nxt - _to);
     return r;
 }
 
-__codecvt_utf8<wchar_t>::result
-__codecvt_utf8<wchar_t>::do_unshift(state_type&,
+__codecvt_utf8_imp<wchar_t, 4>::result
+__codecvt_utf8_imp<wchar_t, 4>::do_unshift(state_type&,
     extern_type* to, extern_type*, extern_type*& to_nxt) const
 {
     to_nxt = to;
@@ -3500,19 +3556,19 @@
 }
 
 int
-__codecvt_utf8<wchar_t>::do_encoding() const noexcept
+__codecvt_utf8_imp<wchar_t, 4>::do_encoding() const  noexcept
 {
     return 0;
 }
 
 bool
-__codecvt_utf8<wchar_t>::do_always_noconv() const noexcept
+__codecvt_utf8_imp<wchar_t, 4>::do_always_noconv() const  noexcept
 {
     return false;
 }
 
 int
-__codecvt_utf8<wchar_t>::do_length(state_type&,
+__codecvt_utf8_imp<wchar_t, 4>::do_length(state_type&,
     const extern_type* frm, const extern_type* frm_end, size_t mx) const
 {
     const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
@@ -3521,7 +3577,7 @@
 }
 
 int
-__codecvt_utf8<wchar_t>::do_max_length() const noexcept
+__codecvt_utf8_imp<wchar_t, 4>::do_max_length() const  noexcept
 {
     if (_Mode_ & consume_header)
         return 7;
@@ -3678,10 +3734,161 @@
     return 4;
 }
 
-// __codecvt_utf16<wchar_t, false>
+// __codecvt_utf16_imp<wchar_t, false, 2>
+
+
+__codecvt_utf16_imp<wchar_t, false, 2>::result
+__codecvt_utf16_imp<wchar_t, false, 2>::do_out(state_type&,
+    const intern_type* frm, const intern_type* frm_end, const intern_type*& frm_nxt,
+    extern_type* to, extern_type* to_end, extern_type*& to_nxt) const
+{
+    const uint16_t* _frm = reinterpret_cast<const uint16_t*>(frm);
+    const uint16_t* _frm_end = reinterpret_cast<const uint16_t*>(frm_end);
+    const uint16_t* _frm_nxt = _frm;
+    uint8_t* _to = reinterpret_cast<uint8_t*>(to);
+    uint8_t* _to_end = reinterpret_cast<uint8_t*>(to_end);
+    uint8_t* _to_nxt = _to;
+    result r = ucs2_to_utf16be(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
+                               _Maxcode_, _Mode_);
+    frm_nxt = frm + (_frm_nxt - _frm);
+    to_nxt = to + (_to_nxt - _to);
+    return r;
+}
+
+__codecvt_utf16_imp<wchar_t, false, 2>::result
+__codecvt_utf16_imp<wchar_t, false, 2>::do_in(state_type&,
+    const extern_type* frm, const extern_type* frm_end, const extern_type*& frm_nxt,
+    intern_type* to, intern_type* to_end, intern_type*& to_nxt) const
+{
+    const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
+    const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
+    const uint8_t* _frm_nxt = _frm;
+    uint16_t* _to = reinterpret_cast<uint16_t*>(to);
+    uint16_t* _to_end = reinterpret_cast<uint16_t*>(to_end);
+    uint16_t* _to_nxt = _to;
+    result r = utf16be_to_ucs2(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
+                               _Maxcode_, _Mode_);
+    frm_nxt = frm + (_frm_nxt - _frm);
+    to_nxt = to + (_to_nxt - _to);
+    return r;
+}
+
+__codecvt_utf16_imp<wchar_t, false, 2>::result
+__codecvt_utf16_imp<wchar_t, false, 2>::do_unshift(state_type&,
+    extern_type* to, extern_type*, extern_type*& to_nxt) const
+{
+    to_nxt = to;
+    return noconv;
+}
+
+int
+__codecvt_utf16_imp<wchar_t, false, 2>::do_encoding() const  noexcept
+{
+    return 0;
+}
+
+bool
+__codecvt_utf16_imp<wchar_t, false, 2>::do_always_noconv() const  noexcept
+{
+    return false;
+}
+
+int
+__codecvt_utf16_imp<wchar_t, false, 2>::do_length(state_type&,
+    const extern_type* frm, const extern_type* frm_end, size_t mx) const
+{
+    const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
+    const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
+    return utf16be_to_ucs2_length(_frm, _frm_end, mx, _Maxcode_, _Mode_);
+}
+
+int
+__codecvt_utf16_imp<wchar_t, false, 2>::do_max_length() const  noexcept
+{
+    if (_Mode_ & consume_header)
+        return 4;
+    return 2;
+}
+
+// __codecvt_utf16_imp<wchar_t, true, 2>
+
+__codecvt_utf16_imp<wchar_t, true, 2>::result
+__codecvt_utf16_imp<wchar_t, true, 2>::do_out(state_type&,
+    const intern_type* frm, const intern_type* frm_end, const intern_type*& frm_nxt,
+    extern_type* to, extern_type* to_end, extern_type*& to_nxt) const
+{
+    const uint16_t* _frm = reinterpret_cast<const uint16_t*>(frm);
+    const uint16_t* _frm_end = reinterpret_cast<const uint16_t*>(frm_end);
+    const uint16_t* _frm_nxt = _frm;
+    uint8_t* _to = reinterpret_cast<uint8_t*>(to);
+    uint8_t* _to_end = reinterpret_cast<uint8_t*>(to_end);
+    uint8_t* _to_nxt = _to;
+    result r = ucs2_to_utf16le(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
+                               _Maxcode_, _Mode_);
+    frm_nxt = frm + (_frm_nxt - _frm);
+    to_nxt = to + (_to_nxt - _to);
+    return r;
+}
+
+__codecvt_utf16_imp<wchar_t, true, 2>::result
+__codecvt_utf16_imp<wchar_t, true, 2>::do_in(state_type&,
+    const extern_type* frm, const extern_type* frm_end, const extern_type*& frm_nxt,
+    intern_type* to, intern_type* to_end, intern_type*& to_nxt) const
+{
+    const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
+    const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
+    const uint8_t* _frm_nxt = _frm;
+    uint16_t* _to = reinterpret_cast<uint16_t*>(to);
+    uint16_t* _to_end = reinterpret_cast<uint16_t*>(to_end);
+    uint16_t* _to_nxt = _to;
+    result r = utf16le_to_ucs2(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
+                               _Maxcode_, _Mode_);
+    frm_nxt = frm + (_frm_nxt - _frm);
+    to_nxt = to + (_to_nxt - _to);
+    return r;
+}
+
+__codecvt_utf16_imp<wchar_t, true, 2>::result
+__codecvt_utf16_imp<wchar_t, true, 2>::do_unshift(state_type&,
+    extern_type* to, extern_type*, extern_type*& to_nxt) const
+{
+    to_nxt = to;
+    return noconv;
+}
+
+int
+__codecvt_utf16_imp<wchar_t, true, 2>::do_encoding() const  noexcept
+{
+    return 0;
+}
+
+bool
+__codecvt_utf16_imp<wchar_t, true, 2>::do_always_noconv() const  noexcept
+{
+    return false;
+}
+
+int
+__codecvt_utf16_imp<wchar_t, true, 2>::do_length(state_type&,
+    const extern_type* frm, const extern_type* frm_end, size_t mx) const
+{
+    const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
+    const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
+    return utf16le_to_ucs2_length(_frm, _frm_end, mx, _Maxcode_, _Mode_);
+}
+
+int
+__codecvt_utf16_imp<wchar_t, true, 2>::do_max_length() const  noexcept
+{
+    if (_Mode_ & consume_header)
+        return 4;
+    return 2;
+}
+
+// __codecvt_utf16_imp<wchar_t, false, 4>
 
-__codecvt_utf16<wchar_t, false>::result
-__codecvt_utf16<wchar_t, false>::do_out(state_type&,
+__codecvt_utf16_imp<wchar_t, false, 4>::result
+__codecvt_utf16_imp<wchar_t, false, 4>::do_out(state_type&,
     const intern_type* frm, const intern_type* frm_end, const intern_type*& frm_nxt,
     extern_type* to, extern_type* to_end, extern_type*& to_nxt) const
 {
@@ -3698,8 +3905,8 @@
     return r;
 }
 
-__codecvt_utf16<wchar_t, false>::result
-__codecvt_utf16<wchar_t, false>::do_in(state_type&,
+__codecvt_utf16_imp<wchar_t, false, 4>::result
+__codecvt_utf16_imp<wchar_t, false, 4>::do_in(state_type&,
     const extern_type* frm, const extern_type* frm_end, const extern_type*& frm_nxt,
     intern_type* to, intern_type* to_end, intern_type*& to_nxt) const
 {
@@ -3716,8 +3923,8 @@
     return r;
 }
 
-__codecvt_utf16<wchar_t, false>::result
-__codecvt_utf16<wchar_t, false>::do_unshift(state_type&,
+__codecvt_utf16_imp<wchar_t, false, 4>::result
+__codecvt_utf16_imp<wchar_t, false, 4>::do_unshift(state_type&,
     extern_type* to, extern_type*, extern_type*& to_nxt) const
 {
     to_nxt = to;
@@ -3725,19 +3932,19 @@
 }
 
 int
-__codecvt_utf16<wchar_t, false>::do_encoding() const noexcept
+__codecvt_utf16_imp<wchar_t, false, 4>::do_encoding() const  noexcept
 {
     return 0;
 }
 
 bool
-__codecvt_utf16<wchar_t, false>::do_always_noconv() const noexcept
+__codecvt_utf16_imp<wchar_t, false, 4>::do_always_noconv() const  noexcept
 {
     return false;
 }
 
 int
-__codecvt_utf16<wchar_t, false>::do_length(state_type&,
+__codecvt_utf16_imp<wchar_t, false, 4>::do_length(state_type&,
     const extern_type* frm, const extern_type* frm_end, size_t mx) const
 {
     const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
@@ -3746,17 +3953,17 @@
 }
 
 int
-__codecvt_utf16<wchar_t, false>::do_max_length() const noexcept
+__codecvt_utf16_imp<wchar_t, false, 4>::do_max_length() const  noexcept
 {
     if (_Mode_ & consume_header)
         return 6;
     return 4;
 }
 
-// __codecvt_utf16<wchar_t, true>
+// __codecvt_utf16_imp<wchar_t, true, 4>
 
-__codecvt_utf16<wchar_t, true>::result
-__codecvt_utf16<wchar_t, true>::do_out(state_type&,
+__codecvt_utf16_imp<wchar_t, true, 4>::result
+__codecvt_utf16_imp<wchar_t, true, 4>::do_out(state_type&,
     const intern_type* frm, const intern_type* frm_end, const intern_type*& frm_nxt,
     extern_type* to, extern_type* to_end, extern_type*& to_nxt) const
 {
@@ -3773,8 +3980,8 @@
     return r;
 }
 
-__codecvt_utf16<wchar_t, true>::result
-__codecvt_utf16<wchar_t, true>::do_in(state_type&,
+__codecvt_utf16_imp<wchar_t, true, 4>::result
+__codecvt_utf16_imp<wchar_t, true, 4>::do_in(state_type&,
     const extern_type* frm, const extern_type* frm_end, const extern_type*& frm_nxt,
     intern_type* to, intern_type* to_end, intern_type*& to_nxt) const
 {
@@ -3791,8 +3998,8 @@
     return r;
 }
 
-__codecvt_utf16<wchar_t, true>::result
-__codecvt_utf16<wchar_t, true>::do_unshift(state_type&,
+__codecvt_utf16_imp<wchar_t, true, 4>::result
+__codecvt_utf16_imp<wchar_t, true, 4>::do_unshift(state_type&,
     extern_type* to, extern_type*, extern_type*& to_nxt) const
 {
     to_nxt = to;
@@ -3800,19 +4007,19 @@
 }
 
 int
-__codecvt_utf16<wchar_t, true>::do_encoding() const noexcept
+__codecvt_utf16_imp<wchar_t, true, 4>::do_encoding() const  noexcept
 {
     return 0;
 }
 
 bool
-__codecvt_utf16<wchar_t, true>::do_always_noconv() const noexcept
+__codecvt_utf16_imp<wchar_t, true, 4>::do_always_noconv() const  noexcept
 {
     return false;
 }
 
 int
-__codecvt_utf16<wchar_t, true>::do_length(state_type&,
+__codecvt_utf16_imp<wchar_t, true, 4>::do_length(state_type&,
     const extern_type* frm, const extern_type* frm_end, size_t mx) const
 {
     const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
@@ -3821,7 +4028,7 @@
 }
 
 int
-__codecvt_utf16<wchar_t, true>::do_max_length() const noexcept
+__codecvt_utf16_imp<wchar_t, true, 4>::do_max_length() const  noexcept
 {
     if (_Mode_ & consume_header)
         return 6;
@@ -4128,10 +4335,86 @@
     return 4;
 }
 
-// __codecvt_utf8_utf16<wchar_t>
+// __codecvt_utf8_utf16_imp<wchar_t, 2>
+
+__codecvt_utf8_utf16_imp<wchar_t, 2>::result
+__codecvt_utf8_utf16_imp<wchar_t, 2>::do_out(state_type&,
+    const intern_type* frm, const intern_type* frm_end, const intern_type*& frm_nxt,
+    extern_type* to, extern_type* to_end, extern_type*& to_nxt) const
+{
+    const uint16_t* _frm = reinterpret_cast<const uint16_t*>(frm);
+    const uint16_t* _frm_end = reinterpret_cast<const uint16_t*>(frm_end);
+    const uint16_t* _frm_nxt = _frm;
+    uint8_t* _to = reinterpret_cast<uint8_t*>(to);
+    uint8_t* _to_end = reinterpret_cast<uint8_t*>(to_end);
+    uint8_t* _to_nxt = _to;
+    result r = utf16_to_utf8(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
+                             _Maxcode_, _Mode_);
+    frm_nxt = frm + (_frm_nxt - _frm);
+    to_nxt = to + (_to_nxt - _to);
+    return r;
+}
+
+__codecvt_utf8_utf16_imp<wchar_t, 2>::result
+__codecvt_utf8_utf16_imp<wchar_t, 2>::do_in(state_type&,
+    const extern_type* frm, const extern_type* frm_end, const extern_type*& frm_nxt,
+    intern_type* to, intern_type* to_end, intern_type*& to_nxt) const
+{
+    const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
+    const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
+    const uint8_t* _frm_nxt = _frm;
+    uint16_t* _to = reinterpret_cast<uint16_t*>(to);
+    uint16_t* _to_end = reinterpret_cast<uint16_t*>(to_end);
+    uint16_t* _to_nxt = _to;
+    result r = utf8_to_utf16(_frm, _frm_end, _frm_nxt, _to, _to_end, _to_nxt,
+                             _Maxcode_, _Mode_);
+    frm_nxt = frm + (_frm_nxt - _frm);
+    to_nxt = to + (_to_nxt - _to);
+    return r;
+}
+
+__codecvt_utf8_utf16_imp<wchar_t, 2>::result
+__codecvt_utf8_utf16_imp<wchar_t, 2>::do_unshift(state_type&,
+    extern_type* to, extern_type*, extern_type*& to_nxt) const
+{
+    to_nxt = to;
+    return noconv;
+}
+
+int
+__codecvt_utf8_utf16_imp<wchar_t, 2>::do_encoding() const  noexcept
+{
+    return 0;
+}
+
+bool
+__codecvt_utf8_utf16_imp<wchar_t, 2>::do_always_noconv() const  noexcept
+{
+    return false;
+}
+
+int
+__codecvt_utf8_utf16_imp<wchar_t, 2>::do_length(state_type&,
+    const extern_type* frm, const extern_type* frm_end, size_t mx) const
+{
+    const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
+    const uint8_t* _frm_end = reinterpret_cast<const uint8_t*>(frm_end);
+    return utf8_to_utf16_length(_frm, _frm_end, mx, _Maxcode_, _Mode_);
+}
+
+int
+__codecvt_utf8_utf16_imp<wchar_t, 2>::do_max_length() const  noexcept
+{
+    if (_Mode_ & consume_header)
+        return 7;
+    return 4;
+}
+
+// __codecvt_utf8_utf16_imp<wchar_t, 4>
+
 
-__codecvt_utf8_utf16<wchar_t>::result
-__codecvt_utf8_utf16<wchar_t>::do_out(state_type&,
+__codecvt_utf8_utf16_imp<wchar_t, 4>::result
+__codecvt_utf8_utf16_imp<wchar_t, 4>::do_out(state_type&,
     const intern_type* frm, const intern_type* frm_end, const intern_type*& frm_nxt,
     extern_type* to, extern_type* to_end, extern_type*& to_nxt) const
 {
@@ -4148,8 +4431,8 @@
     return r;
 }
 
-__codecvt_utf8_utf16<wchar_t>::result
-__codecvt_utf8_utf16<wchar_t>::do_in(state_type&,
+__codecvt_utf8_utf16_imp<wchar_t, 4>::result
+__codecvt_utf8_utf16_imp<wchar_t, 4>::do_in(state_type&,
     const extern_type* frm, const extern_type* frm_end, const extern_type*& frm_nxt,
     intern_type* to, intern_type* to_end, intern_type*& to_nxt) const
 {
@@ -4166,8 +4449,8 @@
     return r;
 }
 
-__codecvt_utf8_utf16<wchar_t>::result
-__codecvt_utf8_utf16<wchar_t>::do_unshift(state_type&,
+__codecvt_utf8_utf16_imp<wchar_t, 4>::result
+__codecvt_utf8_utf16_imp<wchar_t, 4>::do_unshift(state_type&,
     extern_type* to, extern_type*, extern_type*& to_nxt) const
 {
     to_nxt = to;
@@ -4175,19 +4458,19 @@
 }
 
 int
-__codecvt_utf8_utf16<wchar_t>::do_encoding() const noexcept
+__codecvt_utf8_utf16_imp<wchar_t, 4>::do_encoding() const  noexcept
 {
     return 0;
 }
 
 bool
-__codecvt_utf8_utf16<wchar_t>::do_always_noconv() const noexcept
+__codecvt_utf8_utf16_imp<wchar_t, 4>::do_always_noconv() const  noexcept
 {
     return false;
 }
 
 int
-__codecvt_utf8_utf16<wchar_t>::do_length(state_type&,
+__codecvt_utf8_utf16_imp<wchar_t, 4>::do_length(state_type&,
     const extern_type* frm, const extern_type* frm_end, size_t mx) const
 {
     const uint8_t* _frm = reinterpret_cast<const uint8_t*>(frm);
@@ -4196,7 +4479,7 @@
 }
 
 int
-__codecvt_utf8_utf16<wchar_t>::do_max_length() const noexcept
+__codecvt_utf8_utf16_imp<wchar_t, 4>::do_max_length() const  noexcept
 {
     if (_Mode_ & consume_header)
         return 7;