CWG2836 Conversion rank of long double and extended floating-point types

Author: burblebee

source/basic.tex

@@ -5778,6 +5778,15 @@
 An extended floating-point type with the same set of values as
 more than one cv-unqualified standard floating-point type
 has a rank equal to the rank of \keyword{double}.
+\begin{tailnote}
+The treatment of \tcode{std::float64_t} differs from
+that of the analoguous \tcode{_Float64} in C,
+for example on platforms where all of
+\tcode{\keyword{long} \keyword{double}},
+\keyword{double}, and
+\tcode{std::float64_t}
+have the same set of values (see \IsoCUndated{}:2024 H.4.2).
+\end{tailnote}
 \end{itemize}
 \begin{note}
 The conversion ranks of floating-point types \tcode{T1} and \tcode{T2}