Merge "Revert "Remove std::char_traits for non-standard types"" into main

1 files changed, 119 insertions, 30 deletions

diff --git a/include/__string b/include/__string
index b7c0767f9..1ddeec714 100644
--- a/include/__string
+++ b/include/__string
@@ -73,37 +73,126 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 // char_traits
 
 template <class _CharT>
-struct char_traits;
-/*
-The Standard does not define the base template for char_traits because it is impossible to provide
-a correct definition for arbitrary character types. Instead, it requires implementations to provide
-specializations for predefined character types like `char`, `wchar_t` and others. We provide this as
-exposition-only to document what members a char_traits specialization should provide:
-{
-    using char_type  = _CharT;
-    using int_type   = ...;
-    using off_type   = ...;
-    using pos_type   = ...;
-    using state_type = ...;
-
-    static void assign(char_type&, const char_type&);
-    static bool eq(char_type, char_type);
-    static bool lt(char_type, char_type);
-
-    static int              compare(const char_type*, const char_type*, size_t);
-    static size_t           length(const char_type*);
-    static const char_type* find(const char_type*, size_t, const char_type&);
-    static char_type*       move(char_type*, const char_type*, size_t);
-    static char_type*       copy(char_type*, const char_type*, size_t);
-    static char_type*       assign(char_type*, size_t, char_type);
-
-    static int_type  not_eof(int_type);
-    static char_type to_char_type(int_type);
-    static int_type  to_int_type(char_type);
-    static bool      eq_int_type(int_type, int_type);
-    static int_type  eof();
+struct _LIBCPP_TEMPLATE_VIS char_traits
+{
+    typedef _CharT    char_type;
+    typedef int       int_type;
+    typedef streamoff off_type;
+    typedef streampos pos_type;
+    typedef mbstate_t state_type;
+
+    static inline void _LIBCPP_CONSTEXPR_AFTER_CXX14
+        assign(char_type& __c1, const char_type& __c2) _NOEXCEPT {__c1 = __c2;}
+    static inline _LIBCPP_CONSTEXPR bool eq(char_type __c1, char_type __c2) _NOEXCEPT
+        {return __c1 == __c2;}
+    static inline _LIBCPP_CONSTEXPR bool lt(char_type __c1, char_type __c2) _NOEXCEPT
+        {return __c1 < __c2;}
+
+    static _LIBCPP_CONSTEXPR_AFTER_CXX14
+    int compare(const char_type* __s1, const char_type* __s2, size_t __n);
+    _LIBCPP_INLINE_VISIBILITY static _LIBCPP_CONSTEXPR_AFTER_CXX14
+    size_t length(const char_type* __s);
+    _LIBCPP_INLINE_VISIBILITY static _LIBCPP_CONSTEXPR_AFTER_CXX14
+    const char_type* find(const char_type* __s, size_t __n, const char_type& __a);
+    static char_type*       move(char_type* __s1, const char_type* __s2, size_t __n);
+    _LIBCPP_INLINE_VISIBILITY
+    static char_type*       copy(char_type* __s1, const char_type* __s2, size_t __n);
+    _LIBCPP_INLINE_VISIBILITY
+    static char_type*       assign(char_type* __s, size_t __n, char_type __a);
+
+    static inline _LIBCPP_CONSTEXPR int_type  not_eof(int_type __c) _NOEXCEPT
+        {return eq_int_type(__c, eof()) ? ~eof() : __c;}
+    static inline _LIBCPP_CONSTEXPR char_type to_char_type(int_type __c) _NOEXCEPT
+        {return char_type(__c);}
+    static inline _LIBCPP_CONSTEXPR int_type  to_int_type(char_type __c) _NOEXCEPT
+        {return int_type(__c);}
+    static inline _LIBCPP_CONSTEXPR bool      eq_int_type(int_type __c1, int_type __c2) _NOEXCEPT
+        {return __c1 == __c2;}
+    static inline _LIBCPP_CONSTEXPR int_type  eof() _NOEXCEPT
+        {return int_type(EOF);}
 };
-*/
+
+template <class _CharT>
+_LIBCPP_CONSTEXPR_AFTER_CXX14 int
+char_traits<_CharT>::compare(const char_type* __s1, const char_type* __s2, size_t __n)
+{
+    for (; __n; --__n, ++__s1, ++__s2)
+    {
+        if (lt(*__s1, *__s2))
+            return -1;
+        if (lt(*__s2, *__s1))
+            return 1;
+    }
+    return 0;
+}
+
+template <class _CharT>
+inline
+_LIBCPP_CONSTEXPR_AFTER_CXX14 size_t
+char_traits<_CharT>::length(const char_type* __s)
+{
+    size_t __len = 0;
+    for (; !eq(*__s, char_type(0)); ++__s)
+        ++__len;
+    return __len;
+}
+
+template <class _CharT>
+inline
+_LIBCPP_CONSTEXPR_AFTER_CXX14 const _CharT*
+char_traits<_CharT>::find(const char_type* __s, size_t __n, const char_type& __a)
+{
+    for (; __n; --__n)
+    {
+        if (eq(*__s, __a))
+            return __s;
+        ++__s;
+    }
+    return 0;
+}
+
+template <class _CharT>
+_CharT*
+char_traits<_CharT>::move(char_type* __s1, const char_type* __s2, size_t __n)
+{
+    char_type* __r = __s1;
+    if (__s1 < __s2)
+    {
+        for (; __n; --__n, ++__s1, ++__s2)
+            assign(*__s1, *__s2);
+    }
+    else if (__s2 < __s1)
+    {
+        __s1 += __n;
+        __s2 += __n;
+        for (; __n; --__n)
+            assign(*--__s1, *--__s2);
+    }
+    return __r;
+}
+
+template <class _CharT>
+inline
+_CharT*
+char_traits<_CharT>::copy(char_type* __s1, const char_type* __s2, size_t __n)
+{
+    _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
+    char_type* __r = __s1;
+    for (; __n; --__n, ++__s1, ++__s2)
+        assign(*__s1, *__s2);
+    return __r;
+}
+
+template <class _CharT>
+inline
+_CharT*
+char_traits<_CharT>::assign(char_type* __s, size_t __n, char_type __a)
+{
+    char_type* __r = __s;
+    for (; __n; --__n, ++__s)
+        assign(*__s, __a);
+    return __r;
+}
 
 // char_traits<char>