Implement P0298R3: `std::byte`

[mclow.lists]

Summary

Implement std::byte from the paper http://wg21.link/P0298R3.

Split the implementation across two files; putting the stuff that needs enable_if into <type_traits> and the rest in <cstddef>, where it belongs. Sadly, this means that <cstddef> now includes <type_traits> (at the end).

[mclow.lists]

www/cxx1z_status.html

144

Note: the reason for the churn here is that I sorted them by paper number.
The only significant change in this file is the addition of P0298R3 and P0298R3.

[mclow.lists]

Put the std::byte type in the unadorned namespace std, rather than the versioned one. This matches the behavior of other types that the compiler "knows about", like initializer_list, type_info, bad_alloc and so on.

Thanks to @rsmith for the catch.

[EricWF]

I really dislike the circular dependencies between <cstddef> and <type_traits>. I suspect we can avoid this by only including <stddef.h> in <type_traits>, which would allow <cstddef> to depend on <type_traits>. @mclow.lists Does that sound good to you?

[EricWF]

I still think we can come up with a better include structure, but we have plenty of time to figure that out before the next release.
I see no reason to hold this up.

@mclow.lists is there a feature test macro we should be implementing?

[EricWF]

test/std/language.support/support.types/byteops/xor.assign.pass.cpp

13

Nit. These should be // UNSUPPORTED. XFAIL is for bugs we need to fix.

[mclow.lists]

Committed as revision 298689

[mehdi_amini]

test/std/language.support/support.types/byteops/xor.assign.pass.cpp

13

I have mixed feeling about this, in some case I have a test that I want to make sure works in some conditions and does not in other. Using UNSUPPORTED will "hide" such cases if they're unexpectingly passing.

Having to duplicate the test identically in a ".failed.cpp" with a REQUIRE: identical to the UNSUPPORTED in the .pass.cpp is adding some unnecessary overhead and maintenance burden as well.

[jyknight]

I believe this needs compiler support, too, in order to treat

namespace std { enum class byte : unsigned char {}; }

as directly having tbaa type "omnipotent char" instead of a subtype.

That is, given:

void foo(char* x, int *y) {
  x[1] = char(y[0] & 0xff);
  x[0] = char((y[0] & 0xff00) >> 8);
}

the compiler assumes that x and y might alias each-other, and thus must have two loads of y[0]. If you replace "char" with "std::byte", the same should happen, but as of now does not.

[jyknight]

Ping. I don't think this got resolved, and I really wouldn't like to see released in this state...can you either revert this from the library, or implement the compiler support, before the 5.0 release branch?

In D31022#716702, @jyknight wrote:

I believe this needs compiler support, too, in order to treat

namespace std { enum class byte : unsigned char {}; }

as directly having tbaa type "omnipotent char" instead of a subtype.

That is, given:

void foo(char* x, int *y) {
  x[1] = char(y[0] & 0xff);
  x[0] = char((y[0] & 0xff00) >> 8);
}

the compiler assumes that x and y might alias each-other, and thus must have two loads of y[0]. If you replace "char" with "std::byte", the same should happen, but as of now does not.

include/cstddef

     size_t
     max_align_t
     nullptr_t
+    byte // C++17
 
 }  // std
 

 
 _LIBCPP_END_NAMESPACE_STD
 
+#if _LIBCPP_STD_VER > 14
+namespace std  // purposefully not versioned
+{
+enum class byte : unsigned char {};
+
+constexpr byte& operator|=(byte& __lhs, byte __rhs) noexcept
+{ return __lhs = byte(static_cast<unsigned char>(__lhs) | static_cast<unsigned char>(__rhs)); }
+constexpr byte  operator| (byte  __lhs, byte __rhs) noexcept
+{ return         byte(static_cast<unsigned char>(__lhs) | static_cast<unsigned char>(__rhs)); }
+
+constexpr byte& operator&=(byte& __lhs, byte __rhs) noexcept
+{ return __lhs = byte(static_cast<unsigned char>(__lhs) & static_cast<unsigned char>(__rhs)); }
+constexpr byte  operator& (byte  __lhs, byte __rhs) noexcept
+{ return         byte(static_cast<unsigned char>(__lhs) & static_cast<unsigned char>(__rhs)); }
+
+constexpr byte& operator^=(byte& __lhs, byte __rhs) noexcept 
+{ return __lhs = byte(static_cast<unsigned char>(__lhs) ^ static_cast<unsigned char>(__rhs)); }
+constexpr byte  operator^ (byte  __lhs, byte __rhs) noexcept
+{ return         byte(static_cast<unsigned char>(__lhs) ^ static_cast<unsigned char>(__rhs)); }
+
+constexpr byte  operator~ (byte __b) noexcept
+{ return  byte(~static_cast<unsigned char>(__b)); }
+
+}
+
+#include <type_traits>  // rest of byte
+#endif
+
 #endif  // _LIBCPP_CSTDDEF

include/type_traits

 
 _LIBCPP_END_NAMESPACE_STD
 
+#if _LIBCPP_STD_VER > 14
+// std::byte
+namespace std  // purposefully not versioned
+{
+template <class _Integer>
+  constexpr typename enable_if<is_integral_v<_Integer>, byte>::type &
+  operator<<=(byte& __lhs, _Integer __shift) noexcept
+  { return __lhs = byte(static_cast<unsigned char>(__lhs) << __shift); }
+  
+template <class _Integer>
+  constexpr typename enable_if<is_integral_v<_Integer>, byte>::type
+  operator<< (byte  __lhs, _Integer __shift) noexcept
+  { return         byte(static_cast<unsigned char>(__lhs) << __shift); }
+
+template <class _Integer>
+  constexpr typename enable_if<is_integral_v<_Integer>, byte>::type &
+  operator>>=(byte& __lhs, _Integer __shift) noexcept
+  { return __lhs = byte(static_cast<unsigned char>(__lhs) >> __shift); }
+
+template <class _Integer>
+  constexpr typename enable_if<is_integral_v<_Integer>, byte>::type
+  operator>> (byte  __lhs, _Integer __shift) noexcept
+  { return         byte(static_cast<unsigned char>(__lhs) >> __shift); }
+  
+template <class _Integer>
+  constexpr typename enable_if<is_integral_v<_Integer>, _Integer>::type
+  to_integer(byte __b) noexcept { return _Integer(__b); }
+
+}
+#endif
+
 #endif  // _LIBCPP_TYPE_TRAITS

test/std/language.support/support.types/byte.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <type_traits>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// std::byte is not an integer type, nor a character type. 
+// It is a distinct type for accessing the bits that ultimately make up object storage.
+
+static_assert( std::is_pod<std::byte>::value, "" );
+static_assert(!std::is_arithmetic<std::byte>::value, "" );
+static_assert(!std::is_integral<std::byte>::value, "" );
+
+static_assert(!std::is_same<std::byte,          char>::value, "" );
+static_assert(!std::is_same<std::byte,   signed char>::value, "" );
+static_assert(!std::is_same<std::byte, unsigned char>::value, "" );
+
+// The standard doesn't outright say this, but it's pretty clear that it has to be true.
+static_assert(sizeof(std::byte) == 1, "" );
+
+int main () {}

test/std/language.support/support.types/byteops/and.assign.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// constexpr byte& operator &=(byte l, byte r) noexcept;
+
+
+constexpr std::byte test(std::byte b1, std::byte b2) {
+  std::byte bret = b1;
+  return bret &= b2;
+  }
+
+
+int main () {
+  std::byte b;  // not constexpr, just used in noexcept check
+  constexpr std::byte b1{1};
+  constexpr std::byte b8{8};
+  constexpr std::byte b9{9};
+
+  static_assert(noexcept(b &= b), "" );
+
+  static_assert(std::to_integer<int>(test(b1, b8)) == 0, "");
+  static_assert(std::to_integer<int>(test(b1, b9)) == 1, "");
+  static_assert(std::to_integer<int>(test(b8, b9)) == 8, "");
+
+  static_assert(std::to_integer<int>(test(b8, b1)) == 0, "");
+  static_assert(std::to_integer<int>(test(b9, b1)) == 1, "");
+  static_assert(std::to_integer<int>(test(b9, b8)) == 8, "");
+}

test/std/language.support/support.types/byteops/and.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// constexpr byte operator&(byte l, byte r) noexcept;
+
+int main () {
+  constexpr std::byte b1{1};
+  constexpr std::byte b8{8};
+  constexpr std::byte b9{9};
+
+  static_assert(noexcept(b1 & b8), "" );
+
+  static_assert(std::to_integer<int>(b1 & b8) ==  0, "");
+  static_assert(std::to_integer<int>(b1 & b9) ==  1, "");
+  static_assert(std::to_integer<int>(b8 & b9) ==  8, "");
+
+  static_assert(std::to_integer<int>(b8 & b1) ==  0, "");
+  static_assert(std::to_integer<int>(b9 & b1) ==  1, "");
+  static_assert(std::to_integer<int>(b9 & b8) ==  8, "");
+}

test/std/language.support/support.types/byteops/lshift.assign.fail.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// template <class IntegerType>
+//   constexpr byte& operator<<=(byte& b, IntegerType shift) noexcept;
+// This function shall not participate in overload resolution unless 
+//   is_integral_v<IntegerType> is true.
+
+
+constexpr std::byte test(std::byte b) {
+  return b <<= 2.0;
+  }
+
+
+int main () {
+  constexpr std::byte b1 = test(std::byte{1});
+}

test/std/language.support/support.types/byteops/lshift.assign.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// template <class IntegerType>
+//   constexpr byte& operator<<=(byte& b, IntegerType shift) noexcept;
+// This function shall not participate in overload resolution unless 
+//   is_integral_v<IntegerType> is true.
+
+
+constexpr std::byte test(std::byte b) {
+  return b <<= 2;
+  }
+
+
+int main () {
+  std::byte b;  // not constexpr, just used in noexcept check
+  constexpr std::byte b2{2};
+  constexpr std::byte b3{3};
+
+  static_assert(noexcept(b <<= 2), "" );
+  
+  static_assert(std::to_integer<int>(test(b2)) ==  8, "" );
+  static_assert(std::to_integer<int>(test(b3)) == 12, "" );
+
+}

test/std/language.support/support.types/byteops/lshift.fail.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// template <class IntegerType>
+//    constexpr byte operator <<(byte b, IntegerType shift) noexcept;
+// These functions shall not participate in overload resolution unless 
+//   is_integral_v<IntegerType> is true.
+
+int main () {
+  constexpr std::byte b1{1};
+  constexpr std::byte b2 = b1 << 2.0f;
+}

test/std/language.support/support.types/byteops/lshift.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// template <class IntegerType>
+//    constexpr byte operator <<(byte b, IntegerType shift) noexcept;
+// These functions shall not participate in overload resolution unless 
+//   is_integral_v<IntegerType> is true.
+
+int main () {
+  constexpr std::byte b1{1};
+  constexpr std::byte b3{3};
+  
+  static_assert(noexcept(b3 << 2), "" );
+
+  static_assert(std::to_integer<int>(b1 << 1) ==   2, "");
+  static_assert(std::to_integer<int>(b1 << 2) ==   4, "");
+  static_assert(std::to_integer<int>(b3 << 4) ==  48, "");
+  static_assert(std::to_integer<int>(b3 << 6) == 192, "");  
+}

test/std/language.support/support.types/byteops/not.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// constexpr byte operator~(byte b) noexcept;
+
+int main () {
+  constexpr std::byte b1{1};
+  constexpr std::byte b2{2};
+  constexpr std::byte b8{8};
+
+  static_assert(noexcept(~b1), "" );
+
+  static_assert(std::to_integer<int>(~b1) == 254, "");
+  static_assert(std::to_integer<int>(~b2) == 253, "");
+  static_assert(std::to_integer<int>(~b8) == 247, "");
+}

test/std/language.support/support.types/byteops/or.assign.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// constexpr byte& operator |=(byte l, byte r) noexcept;
+
+
+constexpr std::byte test(std::byte b1, std::byte b2) {
+  std::byte bret = b1;
+  return bret |= b2;
+  }
+
+
+int main () {
+  std::byte b;  // not constexpr, just used in noexcept check
+  constexpr std::byte b1{1};
+  constexpr std::byte b2{2};
+  constexpr std::byte b8{8};
+
+  static_assert(noexcept(b |= b), "" );
+
+  static_assert(std::to_integer<int>(test(b1, b2)) ==  3, "");
+  static_assert(std::to_integer<int>(test(b1, b8)) ==  9, "");
+  static_assert(std::to_integer<int>(test(b2, b8)) == 10, "");
+
+  static_assert(std::to_integer<int>(test(b2, b1)) ==  3, "");
+  static_assert(std::to_integer<int>(test(b8, b1)) ==  9, "");
+  static_assert(std::to_integer<int>(test(b8, b2)) == 10, "");
+
+}

test/std/language.support/support.types/byteops/or.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// constexpr byte operator|(byte l, byte r) noexcept;
+
+int main () {
+  constexpr std::byte b1{1};
+  constexpr std::byte b2{2};
+  constexpr std::byte b8{8};
+
+  static_assert(noexcept(b1 | b2), "" );
+
+  static_assert(std::to_integer<int>(b1 | b2) ==  3, "");
+  static_assert(std::to_integer<int>(b1 | b8) ==  9, "");
+  static_assert(std::to_integer<int>(b2 | b8) == 10, "");
+
+  static_assert(std::to_integer<int>(b2 | b1) ==  3, "");
+  static_assert(std::to_integer<int>(b8 | b1) ==  9, "");
+  static_assert(std::to_integer<int>(b8 | b2) == 10, "");
+}

test/std/language.support/support.types/byteops/rshift.assign.fail.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// template <class IntegerType>
+//   constexpr byte operator>>(byte& b, IntegerType shift) noexcept;
+// This function shall not participate in overload resolution unless 
+//   is_integral_v<IntegerType> is true.
+
+
+constexpr std::byte test(std::byte b) {
+  return b >>= 2.0;
+  }
+
+
+int main () {
+  constexpr std::byte b1 = test(std::byte{1});
+}

test/std/language.support/support.types/byteops/rshift.assign.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// template <class IntegerType>
+//   constexpr byte& operator>>=(byte& b, IntegerType shift) noexcept;
+// This function shall not participate in overload resolution unless 
+//   is_integral_v<IntegerType> is true.
+
+
+constexpr std::byte test(std::byte b) {
+  return b >>= 2;
+  }
+
+
+int main () {
+  std::byte b;  // not constexpr, just used in noexcept check
+  constexpr std::byte b16{16};
+  constexpr std::byte b192{192};
+
+  static_assert(noexcept(b >>= 2), "" );
+
+  static_assert(std::to_integer<int>(test(b16))  ==  4, "" );
+  static_assert(std::to_integer<int>(test(b192)) == 48, "" );
+}

test/std/language.support/support.types/byteops/rshift.fail.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// template <class IntegerType>
+//    constexpr byte operator >>(byte b, IntegerType shift) noexcept;
+// These functions shall not participate in overload resolution unless 
+//   is_integral_v<IntegerType> is true.
+
+int main () {
+  constexpr std::byte b1{1};
+  constexpr std::byte b2 = b1 >> 2.0f;
+}

test/std/language.support/support.types/byteops/rshift.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// template <class IntegerType>
+//    constexpr byte operator <<(byte b, IntegerType shift) noexcept;
+// These functions shall not participate in overload resolution unless 
+//   is_integral_v<IntegerType> is true.
+
+
+constexpr std::byte test(std::byte b) {
+  return b <<= 2;
+  }
+
+
+int main () {
+  constexpr std::byte b100{100};
+  constexpr std::byte b115{115};
+  
+  static_assert(noexcept(b100 << 2), "" );
+
+  static_assert(std::to_integer<int>(b100 >> 1) ==  50, "");
+  static_assert(std::to_integer<int>(b100 >> 2) ==  25, "");
+  static_assert(std::to_integer<int>(b115 >> 3) ==  14, "");
+  static_assert(std::to_integer<int>(b115 >> 6) ==   1, "");  
+
+}

test/std/language.support/support.types/byteops/to_integer.fail.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+
+// template <class IntegerType>
+//    constexpr IntegerType to_integer(byte b) noexcept;
+// This function shall not participate in overload resolution unless 
+//   is_integral_v<IntegerType> is true.
+
+int main () {
+  constexpr std::byte b1{1};
+  auto f = std::to_integer<float>(b1);
+}

test/std/language.support/support.types/byteops/to_integer.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// template <class IntegerType>
+//    constexpr IntegerType to_integer(byte b) noexcept;
+// This function shall not participate in overload resolution unless 
+//   is_integral_v<IntegerType> is true.
+
+int main () {
+  constexpr std::byte b1{1};
+  constexpr std::byte b3{3};
+  
+  static_assert(noexcept(std::to_integer<int>(b1)), "" );
+  static_assert(std::is_same<int, decltype(std::to_integer<int>(b1))>::value, "" );
+  static_assert(std::is_same<long, decltype(std::to_integer<long>(b1))>::value, "" );
+  static_assert(std::is_same<unsigned short, decltype(std::to_integer<unsigned short>(b1))>::value, "" );
+
+  static_assert(std::to_integer<int>(b1) == 1, "");
+  static_assert(std::to_integer<int>(b3) == 3, "");
+}

test/std/language.support/support.types/byteops/xor.assign.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// constexpr byte& operator ^=(byte l, byte r) noexcept;
+
+
+constexpr std::byte test(std::byte b1, std::byte b2) {
+  std::byte bret = b1;
+  return bret ^= b2;
+  }
+
+
+int main () {
+  std::byte b;  // not constexpr, just used in noexcept check
+  constexpr std::byte b1{1};
+  constexpr std::byte b8{8};
+  constexpr std::byte b9{9};
+
+  static_assert(noexcept(b ^= b), "" );
+
+  static_assert(std::to_integer<int>(test(b1, b8)) == 9, "");
+  static_assert(std::to_integer<int>(test(b1, b9)) == 8, "");
+  static_assert(std::to_integer<int>(test(b8, b9)) == 1, "");
+
+  static_assert(std::to_integer<int>(test(b8, b1)) == 9, "");
+  static_assert(std::to_integer<int>(test(b9, b1)) == 8, "");
+  static_assert(std::to_integer<int>(test(b9, b8)) == 1, "");
+}

test/std/language.support/support.types/byteops/xor.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+#include <cstddef>
+#include <test_macros.h>
+
+// XFAIL: c++98, c++03, c++11, c++14
+
+// constexpr byte operator^(byte l, byte r) noexcept;
+
+int main () {
+  constexpr std::byte b1{1};
+  constexpr std::byte b8{8};
+  constexpr std::byte b9{9};
+
+  static_assert(noexcept(b1 ^ b8), "" );
+
+  static_assert(std::to_integer<int>(b1 ^ b8) == 9, "");
+  static_assert(std::to_integer<int>(b1 ^ b9) == 8, "");
+  static_assert(std::to_integer<int>(b8 ^ b9) == 1, "");
+
+  static_assert(std::to_integer<int>(b8 ^ b1) == 9, "");
+  static_assert(std::to_integer<int>(b9 ^ b1) == 8, "");
+  static_assert(std::to_integer<int>(b9 ^ b8) == 1, "");
+}

www/cxx1z_status.html

     <tr><td></td><td></td><td></td><td></td><td></td><td></td></tr>
   <tr><td><a href="http://wg21.link/P0156R2">P0156R2</a></td><td>LWG</td><td>Variadic Lock guard</td><td>Kona</td><td></td><td></td></tr>
   <tr><td><a href="http://wg21.link/P0270R3">P0270R3</a></td><td>CWG</td><td>Removing C dependencies from signal handler wording</td><td>Kona</td><td></td><td></td></tr>
-  <tr><td><a href="http://wg21.link/P0298R3">P0298R3</a></td><td>CWG</td><td>A byte type definition</td><td>Kona</td><td></td><td></td></tr>
+  <tr><td><a href="http://wg21.link/P0298R3">P0298R3</a></td><td>CWG</td><td>A byte type definition</td><td>Kona</td><td>Complete</td><td>5.0</td></tr>
   <tr><td><a href="http://wg21.link/P0317R1">P0317R1</a></td><td>LWG</td><td>Directory Entry Caching for Filesystem</td><td>Kona</td><td></td><td></td></tr>
   <tr><td><a href="http://wg21.link/P0430R2">P0430R2</a></td><td>LWG</td><td>File system library on non-POSIX-like operating systems</td><td>Kona</td><td></td><td></td></tr>
   <tr><td><a href="http://wg21.link/P0433R2">P0433R2</a></td><td>LWG</td><td>Toward a resolution of US7 and US14: Integrating template deduction for class templates into the standard library</td><td>Kona</td><td></td><td></td></tr>