P0463R1 Endian, just endian

Editorial changes: Added section comment in the synopsis, changed "either ... nor" to "either ... or" in the new paragraph 2.

Author: tkoeppe

source/utilities.tex

@@ -15478,6 +15478,13 @@
   template<class... B> struct disjunction;
   template<class B> struct negation;
 
+  // \ref{meta.endian}, endian
+  enum class endian {
+    little = @\seebelow@,
+    big    = @\seebelow@,
+    native = @\seebelow@
+  };
+
   // \ref{meta.unary.cat}, primary type categories
   template <class T> inline constexpr bool is_void_v
     = is_void<T>::value;
@@ -17096,6 +17103,42 @@
 is a \tcode{UnaryTypeTrait} with a base characteristic of \tcode{bool_constant<!bool(B::value)>}.
 \end{itemdescr}
 
+\rSec2[meta.endian]{Endian}
+
+\pnum
+Two common methods of byte ordering in multibyte scalar types are big-endian
+and little-endian in the execution environment. Big-endian is a format for
+storage of binary data in which the most significant byte is placed first,
+with the rest in descending order. Little-endian is a format for storage of
+binary data in which the least significant byte is placed first, with the rest
+in ascending order. This subclause describes the endianness of the scalar types
+of the execution environment.
+
+\indexlibrary{\idxcode{endian}}%
+\indexlibrarymember{little}{endian}%
+\indexlibrarymember{big}{endian}%
+\indexlibrarymember{native}{endian}%
+\begin{itemdecl}
+enum class endian {
+  little = @\seebelow@,
+  big    = @\seebelow@,
+  native = @\seebelow@
+};
+\end{itemdecl}
+
+\begin{itemdescr}
+\pnum
+If all scalar types have size \tcode{1}, then all of \tcode{endian::little},
+\tcode{endian::big}, and \tcode{endian::native} have the same value.
+Otherwise \tcode{endian::little} shall not be equal to \tcode{endian::big}.
+If all scalar types are big-endian, \tcode{endian::native} shall be
+equal to \tcode{endian::big}.
+If all scalar types are little-endian, \tcode{endian::native} shall be
+equal to \tcode{endian::little}.
+Otherwise \tcode{endian::native} shall have a value that is not equal
+to either of \tcode{endian::big} or \tcode{endian::little}.
+\end{itemdescr}
+
 \rSec1[ratio]{Compile-time rational arithmetic}
 
 \rSec2[ratio.general]{In general}