Implement P0463R1: 'Endian just Endian'. Reviewed as https://reviews.llvm.org/D35472

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@323296 91177308-0d34-0410-b5e6-96231b3b80d8

include/type_traits

@@ -4941,6 +4941,21 @@ struct __can_extract_map_key<_ValTy, _Key, _Key, _RawValTy>
 
 #endif
 
+#if _LIBCPP_STD_VER > 17
+enum class endian
+{
+    little = 0xDEAD,
+    big    = 0xFACE,
+#if defined(_LIBCPP_LITTLE_ENDIAN)
+    native = little
+#elif defined(_LIBCPP_BIG_ENDIAN)
+    native = big
+#else
+    native = 0xCAFE
+#endif
+};
+#endif
+
 _LIBCPP_END_NAMESPACE_STD
 
 #if _LIBCPP_STD_VER > 14

test/std/utilities/meta/meta.type.synop/endian.pass.cpp

@@ -0,0 +1,47 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
+
+// enum class endian;
+
+#include <type_traits>
+#include <cstring>
+#include <cassert>
+
+#include "test_macros.h"
+
+int main() {
+    typedef std::endian E;
+    static_assert(std::is_enum<std::endian>::value, "");
+
+// Check that E is a scoped enum by checking for conversions.
+    typedef std::underlying_type<std::endian>::type UT;
+    static_assert(!std::is_convertible<std::endian, UT>::value, "");
+
+// test that the enumeration values exist
+    static_assert( std::endian::little == std::endian::little );
+    static_assert( std::endian::big    == std::endian::big );
+    static_assert( std::endian::native == std::endian::native );
+    static_assert( std::endian::little != std::endian::big );
+
+//  Technically not required, but true on all existing machines
+    static_assert( std::endian::native == std::endian::little || 
+                   std::endian::native == std::endian::big );
+    
+//  Try to check at runtime
+    {
+    uint32_t i = 0x01020304;
+    char c[4];
+    static_assert(sizeof(i) == sizeof(c));
+    std::memcpy(c, &i, sizeof(c));
+
+    assert ((c[0] == 1) == (std::endian::native == std::endian::big));
+    }
+}