P0533R9 constexpr for <cmath> and <cstdlib>

Author: jensmaurer

source/expressions.tex

@@ -7362,7 +7362,11 @@
 an \grammarterm{asm-declaration}\iref{dcl.asm};
 
 \item
-an invocation of the \tcode{va_arg} macro\iref{cstdarg.syn}; or
+an invocation of the \tcode{va_arg} macro\iref{cstdarg.syn};
+
+\item
+a non-constant library call\iref{defns.nonconst.libcall};
+or
 
 \item
 a \keyword{goto} statement\iref{stmt.goto}.

source/intro.tex

@@ -423,6 +423,12 @@
 sequence of one or more bytes representing
 the code unit sequence for an encoded character of the execution character set
 
+\indexdefn{library call!non-constant}%
+\definition{non-constant library call}{defns.nonconst.libcall}
+invocation of a library function that,
+as part of evaluating any expression \tcode{E},
+prevents \tcode{E} from being a core constant expression
+
 \definition{NTCTS}{defns.ntcts}
 \defncontext{library}
 \indexdefn{NTCTS}%

source/lib-intro.tex

@@ -136,6 +136,30 @@
 ISO C \tcode{restrict} qualifier)
 are the same unless otherwise stated.
 
+\pnum
+A call to a C standard library function is
+a non-constant library call\iref{defns.nonconst.libcall}
+if it raises a floating-point exception other than \tcode{FE_INEXACT}.
+The semantics of a call to a C standard library function
+evaluated as a core constant expression
+are those specified in Annex F of the C standard
+\begin{footnote}
+See also ISO/IEC 9899:2018 section 7.6.
+\end{footnote}
+to the extent applicable to the floating-point types\iref{basic.fundamental}
+that are parameter types of the called function.
+\begin{note}
+Annex F specifies
+the conditions under which floating-point exceptions are raised and
+the behavior when NaNs and/or infinities are passed as arguments.
+\end{note}
+\begin{note}
+Equivalently, a call to a C standard library function is
+a non-constant library call
+if \tcode{errno} is set
+when math \tcode{errhandling \& MATH ERRNO} is \tcode{true}.
+\end{note}
+
 \rSec1[description]{Method of description}
 
 \rSec2[description.general]{General}