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    CWG Issue 2864</TITLE>
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<P><EM>This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21
  Core Issues List revision 118b.
  See http://www.open-std.org/jtc1/sc22/wg21/ for the official
  list.</EM></P>
<P>2025-09-28</P>
<HR>
<A NAME="2864"></A><H4>2864.
  
Narrowing floating-point conversions
</H4>
<B>Section: </B>9.5.5&#160; [<A href="https://wg21.link/dcl.init.list">dcl.init.list</A>]
 &#160;&#160;&#160;

 <B>Status: </B>CD7
 &#160;&#160;&#160;

 <B>Submitter: </B>Brian Bi
 &#160;&#160;&#160;

 <B>Date: </B>2023-11-04<BR>


<P>[Accepted as a DR at the June, 2024 meeting.]</P>



<P>Consider:</P>

<PRE>
  float f = {1e100};
</PRE>

<P>This is rejected as narrowing on all implementations.
<A HREF="2723.html">Issue 2723</A> made the example non-narrowing,
which seems incorrect on an IEEE platform.</P>

<P><B>Proposed resolution (approved by CWG 2024-04-19):</B></P>

<P>Change in 9.5.5 [<A href="https://wg21.link/dcl.init.list#7">dcl.init.list</A>] paragraph 7 as follows:</P>

<BLOCKQUOTE>

A <I>narrowing conversion</I> is an implicit conversion
<UL>
<LI>from a floating-point type to an integer type, or</LI>
<LI>from a floating-point type T to another floating-point type whose
floating-point conversion rank is neither greater than nor equal to
that of T, except where the <DEL>source</DEL> <INS>result of the
conversion</INS> is a constant expression and <DEL>the
actual</DEL> <INS>either its</INS> value <DEL>after conversion</DEL>
is <INS>finite and</INS> <DEL>within the range of values that can be
represented (even if it cannot be represented exactly)</DEL> <INS>the
conversion did not overflow, or the values before and after the
conversion are not finite</INS>, or</LI>
<LI>from an integer type ...</LI>
</UL>

</BLOCKQUOTE>

<P><B>Additional notes (April, 2024)</B></P>

<P>According to the proposed wording, since NaNs are not finite,
conversion of NaNs is always non-narrowing.  However, the payload of
the NaN might not be preserved when converting to a smaller
floating-point type.</P>

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