C++20 constexpr _Copy_s and simplify char8_t compare

stl/inc/xstring

@@ -65,7 +65,8 @@ struct _Char_traits { // properties of a string or stream element
         return _First1;
     }
 
-    _Pre_satisfies_(_Dest_size >= _Count) static _Elem* _Copy_s(_Out_writes_all_(_Dest_size) _Elem* const _First1,
+    _Pre_satisfies_(_Dest_size >= _Count) static _CONSTEXPR20 _Elem* _Copy_s(_Out_writes_all_(_Dest_size)
+                                                                                 _Elem* const _First1,
         const size_t _Dest_size, _In_reads_(_Count) const _Elem* const _First2,
         const size_t _Count) noexcept { // copy [_First2, _First2 + _Count) to [_First1, _First1 + _Dest_size)
         _STL_VERIFY(_Count <= _Dest_size, "invalid argument");
@@ -363,14 +364,7 @@ public:
         _In_reads_(_Count) const _Elem* const _First2, const size_t _Count) noexcept /* strengthened */ {
         // compare [_First1, _First1 + _Count) with [_First2, ...)
 #if _HAS_CXX17
-#if _HAS_U8_INTRINSICS
-        if constexpr (is_same_v<_Elem, char8_t>) {
-            return __builtin_u8memcmp(_First1, _First2, _Count);
-        } else
-#endif // _HAS_U8_INTRINSICS
-        {
-            return __builtin_memcmp(_First1, _First2, _Count);
-        }
+        return __builtin_memcmp(_First1, _First2, _Count);
 #else // _HAS_CXX17
         return _CSTD memcmp(_First1, _First2, _Count);
 #endif // _HAS_CXX17
@@ -1372,8 +1366,9 @@ public:
         return _Count;
     }
 
-    _Pre_satisfies_(_Dest_size >= _Count) constexpr size_type _Copy_s(_Out_writes_all_(_Dest_size) _Elem* const _Dest,
-        const size_type _Dest_size, size_type _Count, const size_type _Off = 0) const {
+    _Pre_satisfies_(_Dest_size >= _Count) _CONSTEXPR20 size_type
+        _Copy_s(_Out_writes_all_(_Dest_size) _Elem* const _Dest, const size_type _Dest_size, size_type _Count,
+            const size_type _Off = 0) const {
         // copy [_Off, _Off + _Count) to [_Dest, _Dest + _Count)
         _Check_offset(_Off);
         _Count = _Clamp_suffix_size(_Off, _Count);

tests/std/tests/P0220R1_string_view/test.cpp

@@ -1034,11 +1034,11 @@ static_assert(test_case_iterators<char, constexpr_char_traits>());
 static_assert(test_case_prefix<char, constexpr_char_traits>());
 static_assert(test_case_suffix<char, constexpr_char_traits>());
 static_assert(test_case_swap<char, constexpr_char_traits>());
-static_assert(test_case_Copy_s<constexpr_char_traits>());
 static_assert(test_case_substr<constexpr_char_traits>());
 static_assert(test_case_compare<char, constexpr_char_traits>());
 #if _HAS_CXX20
 static_assert(test_case_copy<constexpr_char_traits>());
+static_assert(test_case_Copy_s<constexpr_char_traits>());
 static_assert(test_case_starts_with_ends_with<char, constexpr_char_traits, false>());
 #endif // _HAS_CXX20
 static_assert(test_case_operators<char, constexpr_char_traits>());

tests/std/tests/P1032R1_miscellaneous_constexpr/test.cpp

@@ -272,7 +272,7 @@ constexpr bool run_tests() {
         assert(last - first == static_cast<ptrdiff_t>(needle.size()));
     }
 
-    // test char_traits move/copy/assign and basic_string_view::copy
+    // test char_traits assign/copy/_Copy_s/move and basic_string_view::copy/_Copy_s
     {
         using Elem   = char;
         using Traits = char_traits<Elem>;
@@ -314,6 +314,15 @@ constexpr bool run_tests() {
 
         assert(Traits::move(buf + 5, buf + 3, 11) == buf + 5); // overlapping, dest after src
         assert(buf == "....a.ababcbabc.c.."sv);
+
+        assert(Traits::_Copy_s(buf, 20, src, 18) == buf);
+        assert(buf == "cute fluffy KITTEN."sv);
+
+        assert(sv._Copy_s(buf, 20, 4, 10) == 4);
+        assert(buf == "abc. fluffy KITTEN."sv);
+
+        assert(sv._Copy_s(buf, 20, 11) == 11);
+        assert(buf == "..........a KITTEN."sv);
     }
 
     {
@@ -357,6 +366,15 @@ constexpr bool run_tests() {
 
         assert(Traits::move(buf + 5, buf + 3, 11) == buf + 5); // overlapping, dest after src
         assert(buf == u"....a.ababcbabc.c.."sv);
+
+        assert(Traits::_Copy_s(buf, 20, src, 18) == buf);
+        assert(buf == u"cute fluffy KITTEN."sv);
+
+        assert(sv._Copy_s(buf, 20, 4, 10) == 4);
+        assert(buf == u"abc. fluffy KITTEN."sv);
+
+        assert(sv._Copy_s(buf, 20, 11) == 11);
+        assert(buf == u"..........a KITTEN."sv);
     }
 
     {
@@ -400,6 +418,15 @@ constexpr bool run_tests() {
 
         assert(Traits::move(buf + 5, buf + 3, 11) == buf + 5); // overlapping, dest after src
         assert(buf == U"....a.ababcbabc.c.."sv);
+
+        assert(Traits::_Copy_s(buf, 20, src, 18) == buf);
+        assert(buf == U"cute fluffy KITTEN."sv);
+
+        assert(sv._Copy_s(buf, 20, 4, 10) == 4);
+        assert(buf == U"abc. fluffy KITTEN."sv);
+
+        assert(sv._Copy_s(buf, 20, 11) == 11);
+        assert(buf == U"..........a KITTEN."sv);
     }
 
     {
@@ -443,6 +470,15 @@ constexpr bool run_tests() {
 
         assert(Traits::move(buf + 5, buf + 3, 11) == buf + 5); // overlapping, dest after src
         assert(buf == L"....a.ababcbabc.c.."sv);
+
+        assert(Traits::_Copy_s(buf, 20, src, 18) == buf);
+        assert(buf == L"cute fluffy KITTEN."sv);
+
+        assert(sv._Copy_s(buf, 20, 4, 10) == 4);
+        assert(buf == L"abc. fluffy KITTEN."sv);
+
+        assert(sv._Copy_s(buf, 20, 11) == 11);
+        assert(buf == L"..........a KITTEN."sv);
     }
 
 #ifdef __cpp_lib_char8_t
@@ -487,9 +523,51 @@ constexpr bool run_tests() {
 
         assert(Traits::move(buf + 5, buf + 3, 11) == buf + 5); // overlapping, dest after src
         assert(buf == u8"....a.ababcbabc.c.."sv);
+
+        assert(Traits::_Copy_s(buf, 20, src, 18) == buf);
+        assert(buf == u8"cute fluffy KITTEN."sv);
+
+        assert(sv._Copy_s(buf, 20, 4, 10) == 4);
+        assert(buf == u8"abc. fluffy KITTEN."sv);
+
+        assert(sv._Copy_s(buf, 20, 11) == 11);
+        assert(buf == u8"..........a KITTEN."sv);
     }
 #endif // __cpp_lib_char8_t
 
+    // test char_traits::compare refactoring through basic_string_view (not part of P1032R1)
+    {
+        assert("cat"sv == "cat"sv);
+        assert("cat"sv < "category"sv);
+        assert("catastrophe"sv > "cat"sv);
+        assert("catch"sv < "category"sv);
+        assert("catenary"sv > "catapult"sv);
+
+        assert(u"cat"sv == u"cat"sv);
+        assert(u"cat"sv < u"category"sv);
+        assert(u"catastrophe"sv > u"cat"sv);
+        assert(u"catch"sv < u"category"sv);
+        assert(u"catenary"sv > u"catapult"sv);
+
+        assert(U"cat"sv == U"cat"sv);
+        assert(U"cat"sv < U"category"sv);
+        assert(U"catastrophe"sv > U"cat"sv);
+        assert(U"catch"sv < U"category"sv);
+        assert(U"catenary"sv > U"catapult"sv);
+
+        assert(L"cat"sv == L"cat"sv);
+        assert(L"cat"sv < L"category"sv);
+        assert(L"catastrophe"sv > L"cat"sv);
+        assert(L"catch"sv < L"category"sv);
+        assert(L"catenary"sv > L"catapult"sv);
+
+        assert(u8"cat"sv == u8"cat"sv);
+        assert(u8"cat"sv < u8"category"sv);
+        assert(u8"catastrophe"sv > u8"cat"sv);
+        assert(u8"catch"sv < u8"category"sv);
+        assert(u8"catenary"sv > u8"catapult"sv);
+    }
+
     return true;
 }