mclow.lists created this revision.
Implement the C++2a feature "A compile time endian-ness detection idiom"
Howard's suggested implementation is:
enum class endian
{
#ifdef _WIN32
little = 0,
big = 1,
native = little
#else
little = __ORDER_LITTLE_ENDIAN__,
big = __ORDER_BIG_ENDIAN__
native = __BYTE_ORDER__,
#endif
};
but libc++ has it's own macros that have done the work to detect this.
The other option would be to rip out `_LIBCPP_LITTLE_ENDIAN` and
`_LIBCPP_BIG_ENDIAN`, which is tempting, but that would entail changes in code
that has to compile for earlier C++ language versions.
https://reviews.llvm.org/D35472
Files:
include/type_traits
test/std/utilities/meta/meta.type.synop/endian.pass.cpp
Index: test/std/utilities/meta/meta.type.synop/endian.pass.cpp
===================================================================
--- test/std/utilities/meta/meta.type.synop/endian.pass.cpp
+++ test/std/utilities/meta/meta.type.synop/endian.pass.cpp
@@ -0,0 +1,46 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++14, c++17
+
+// enum class endian;
+
+#include <type_traits>
+#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
+ {
+ union {
+ uint32_t i;
+ char c[4];
+ } u = {0x01020304};
+
+ assert ((u.c[0] == 1) == (std::endian::native == std::endian::big));
+ }
+}
Index: include/type_traits
===================================================================
--- include/type_traits
+++ include/type_traits
@@ -4737,6 +4737,21 @@
#endif
+#if _LIBCPP_STD_VER > 14
+enum class endian
+{
+ little = 0xDEAD,
+ big = 0xFACE,
+#if _LIBCPP_LITTLE_ENDIAN
+ native = little
+#elif _LIBCPP_BIG_ENDIAN
+ native = big
+#else
+ native = 0xCAFE
+#endif
+};
+#endif
+
_LIBCPP_END_NAMESPACE_STD
#if _LIBCPP_STD_VER > 14
Index: test/std/utilities/meta/meta.type.synop/endian.pass.cpp
===================================================================
--- test/std/utilities/meta/meta.type.synop/endian.pass.cpp
+++ test/std/utilities/meta/meta.type.synop/endian.pass.cpp
@@ -0,0 +1,46 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++14, c++17
+
+// enum class endian;
+
+#include <type_traits>
+#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
+ {
+ union {
+ uint32_t i;
+ char c[4];
+ } u = {0x01020304};
+
+ assert ((u.c[0] == 1) == (std::endian::native == std::endian::big));
+ }
+}
Index: include/type_traits
===================================================================
--- include/type_traits
+++ include/type_traits
@@ -4737,6 +4737,21 @@
#endif
+#if _LIBCPP_STD_VER > 14
+enum class endian
+{
+ little = 0xDEAD,
+ big = 0xFACE,
+#if _LIBCPP_LITTLE_ENDIAN
+ native = little
+#elif _LIBCPP_BIG_ENDIAN
+ native = big
+#else
+ native = 0xCAFE
+#endif
+};
+#endif
+
_LIBCPP_END_NAMESPACE_STD
#if _LIBCPP_STD_VER > 14
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