<!DOCTYPE html><html><head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<div class="moz-cite-prefix">(One side note: I'm not seeing Jan's
messages to the list, only Rajan's replies, and the cfp-interest
numbering marks Rajan's messages as consecutive. Are non-members'
messages sent to some moderation queue?)</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">So my take here is that everything is
actually pretty clear if you understand how everything is supposed
to fit together. But to figure that out, you have to very
carefully read 2 different specifications (3, if you're looking at
C++), and proceed to look in all of the wrong places of those
specifications to figure out what anything even means.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">If we start in IEEE 754, Table 3.1 lays
out 4 different levels of understanding floating-point arithmetic.
Level 1 is extended real numbers, the mathematical system being
approximated. Level 2 refers to floating-point data, where 0 is
broken into -0 and +0, and a single NaN datum is added. Level 3
are floating-point representations, where finite numbers are
broken into (sign, exponent, significand) and NaN is broken into a
qNaN and sNaN. Level 4 is the final bit string layer (encodings).
And then it gets confusing because, having introduced these
layers, the standard then stops referring to them again, and you
have to very carefully parse the wording to work out what level
it's trying to apply semantics to. (In general, IEEE 754 is
largely implicitly describing semantics in terms of floating-point
representations [level 3], although there are some operations
where the standard intends to precisely describe the encoding
[level 4].)</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">As for C, where we need to start is in
fact section 5.3.5.3.3 (Characteristics of floating-point types).
Here we find the definition of floating-point numbers and some
discussion on values. p10 starts by saying "A NaN is a value
signifying Not-A-Number. A quiet NaN propagates..." (note that it
says "a quiet NaN" and not "a quiet NaN value"). Again, here we
start having to do some inference to figure out the intent. A
careful reading of this section indicates that perhaps the best
way to understand it is to map things to IEEE 754's definitions,
mapping non-IEEE 754 types to equivalent IEEE 754 concepts as
appropriate (e.g., NOTE 2).</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">So how do we do the mapping? Again,
careful reading illustrates that there is a difference between
"value" and "representation." The C "representation" corresponds
to level 4 in IEEE 754. The C "value" term is trickier to pin
down, but from 5.3.5.3.4 (Characteristics of decimal
floating-point type) and the discussion of quantum exponents
(particularly p9) lets you infer that "value" corresponds to IEEE
754 level 2: a value is a floating-point datum.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">It is arguable that you could map
"value" to IEEE 754's level 3 (which distinguishes a qNaN from a
sNaN "floating-point representation", annoyingly the same word
that C uses for something different). But arguing that NaNs having
different payloads are distinct values is pretty clearly wrong.
See e.g., EXAMPLE 5 in 6.7.2, where the code has a comment
explicitly saying "quiet NaNs in real floating types are
considered the same value, regardless of payloads," or footnote
453 in F.10.14.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">On 4/16/2026 17:33, RAJAN BHAKTA wrote:<br>
</div>
<blockquote type="cite" cite="mid:BYAPR15MB23263CCC1D3FD565EA96E8729C232@BYAPR15MB2326.namprd15.prod.outlook.com">
<div style="direction: ltr; font-family: Aptos, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Hi Jan,</div>
<div style="direction: ltr; font-family: Aptos, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="direction: ltr; font-family: Aptos, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
I was giving a specific case of value, but the general case I
believe holds: The value of a NaN (signaling or otherwise) is a
NaN (not a number). The signaling or quiet aspects are not a
part of the value. i.e. Section 6.3.2.5 “Real Floating Types" is
concerned with value preservation (e.g., 3.14 remains 3.14,
infinity remains infinity, NaN remains NaN), not with preserving
the signaling/quiet distinction. So the “precise meaning of an
object” is that it’s a NaN. Essentially this is similar to how
various non-canonical representations can all represent the same
value, including ones that provide additional information
outside of the value.</div>
<div style="direction: ltr; font-family: Aptos, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div style="direction: ltr; font-family: Aptos, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
I can see we disagree on this part, and hence it may make sense
to make a change to the standard to make it clear/explicit.</div>
<div style="direction: ltr; font-family: Aptos, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div id="ms-outlook-mobile-signature">
<p class="xxmsonormal" style="margin: 0in;"><span style="color: rgb(33, 33, 33);">Regards,<br>
<br>
<b>Rajan Bhakta</b><br>
CFP</span></p>
<p class="xxmsonormal" style="margin: 0in;"> </p>
</div>
<div id="mail-editor-reference-message-container">
<div class="ms-outlook-mobile-reference-message skipProofing" style="direction: ltr;">
</div>
<div class="ms-outlook-mobile-reference-message skipProofing" style="text-align: left; padding: 3pt 0in 0in; border-width: 1pt medium medium; border-style: solid none none; border-color: rgb(181, 196, 223) currentcolor currentcolor; font-family: Aptos; font-size: 12pt; color: black;">
<b>From: </b>Jan Schultke <a class="moz-txt-link-rfc2396E" href="mailto:janschultke@googlemail.com"><janschultke@googlemail.com></a><br>
<b>Date: </b>Thursday, April 16, 2026 at 2:36 PM<br>
<b>To: </b>RAJAN BHAKTA <a class="moz-txt-link-rfc2396E" href="mailto:rbhakta@us.ibm.com"><rbhakta@us.ibm.com></a><br>
<b>Cc: </b><a class="moz-txt-link-abbreviated" href="mailto:cfp-interest@oakapple.net">cfp-interest@oakapple.net</a>
<a class="moz-txt-link-rfc2396E" href="mailto:cfp-interest@oakapple.net"><cfp-interest@oakapple.net></a><br>
<b>Subject: </b>[EXTERNAL] Re: convertFrom and signaling NaNs<br>
<br>
</div>
<div dir="ltr" lang="en" id="pfptBannerk79hxk1" style="visibility: visible !important; opacity: 1 !important; max-width: none !important; max-height: none !important; display: block !important; text-align: left !important; margin: 0px 0px 10px !important; padding: 7px 16px 8px !important; border-radius: 4px !important; min-width: 200px !important; background-color: rgb(208, 216, 220); border-top-width: 4px !important; border-top-style: solid !important; border-top-color: rgb(144, 164, 174) !important;">
<div id="pfptBannerk79hxk1" style="visibility: visible !important; opacity: 1 !important; background-color: rgb(208, 216, 220); max-height: none !important; float: left !important; display: block !important; margin: 1px 0px !important; max-width: 600px !important;">
<div id="pfptBannerk79hxk1" style="opacity: 1 !important; max-width: none !important; max-height: none !important; display: block !important; visibility: visible !important; background-color: rgb(208, 216, 220); color: rgb(0, 0, 0); font-family: Arial, sans-serif !important; font-weight: bold !important; font-size: 14px !important; line-height: 1.29 !important;">
This Message Is From an Untrusted Sender</div>
<div id="pfptBannerk79hxk1" style="font-weight: normal; opacity: 1 !important; max-width: none !important; max-height: none !important; display: block !important; visibility: visible !important; background-color: rgb(208, 216, 220); color: rgb(0, 0, 0); font-family: Arial, sans-serif !important; font-size: 12px !important; line-height: 1.5 !important; margin-top: 2px !important;">
You have not previously corresponded with this sender.</div>
</div>
<div id="pfptBannerk79hxk1" style="visibility: visible !important; opacity: 1 !important; background-color: rgb(208, 216, 220); max-width: none !important; max-height: none !important; float: right !important; display: block !important; margin-left: 16px !important; margin-top: 1px !important; text-align: right !important; width: fit-content !important; font-size: 12px !important;">
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div style="margin-top: 3px; margin-bottom: 3px; margin-left: 16px; padding: 7.5px 16px; border-width: 1px; border-style: solid; border-color: rgb(102, 102, 102); border-radius: 2px; width: fit-content; display: inline-block;">
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="direction: ltr; white-space: nowrap;">
</div>
<span style="background-color: rgb(208, 216, 220);">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div id="pfptBannerk79hxk1" style="background-color: rgb(208, 216, 220); max-width: none; max-height: none; display: inline-block;">
<div class="pfptPrimaryButtonk79hxk1" style="white-space: nowrap;"><span style="font-family: Arial, sans-serif; font-size: 14px; color: rgb(0, 0, 0);"><a href="https://us-phishalarm-ewt.proofpoint.com/EWT/v1/AdhS1Rd-!-XFVHHo80mE1PTx5QApOe0MNwyUrt8VlzhzyXnGn4Y8_94nA7bR9HcQ1oehNyiAE3Gw7otUUz_hDMhyC04yy7R0Sd-8A4pRdkMHubMqr580uF4xrI1ioZLjfiA$" id="pfptBannerk79hxk1" data-outlook-id="b7349dd2-0696-4010-81ae-bd337d77383e" style="text-decoration: none; display: inline-block; background-color: rgb(208, 216, 220); max-width: none; max-height: none;" moz-do-not-send="true">Report Suspicious</a></span></div>
</div>
</div>
</span></div>
</span></div>
</span></div>
</span></div>
</span></div>
</span></div>
</span></div>
</span></div>
</span></div>
</span></div>
</span></div>
</span></div>
</span></div>
</span></div>
</div>
</span></div>
<div style="line-height: 0; height: 0px; display: block; font-size: 0.01px;"> </div>
</div>
<div class="gmail_default" style="direction: ltr; font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">
<br>
</div>
<blockquote style="margin: 0px 0px 0px 0.8ex; padding-left: 1ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204);">
<div class="gmail_quote" style="direction: ltr; font-family: Aptos, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
Hi,</div>
<div class="gmail_quote" style="direction: ltr; font-family: Aptos, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="gmail_quote" style="direction: ltr; font-family: Aptos, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
How to handle issues for C (WG14) are given at <a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__www.open-2Dstd.org_jtc1_sc22_wg14_issues_&d=DwMFaQ&c=BSDicqBQBDjDI9RkVyTcHQ&r=XTIN0AwPKAf2bIKNxlzdeqggAytE5h-JEusWpx9MXwc&m=Q07maytVJxXWrqyVGB6sEg51yjqEWSF2wU7ccFJXUClAAvfsz6thR6JHnA7eKU3N&s=tNvLT0zA5tU8F2RRX6RwWm3s91cp_o_OPU-YGZEcT84&e=" target="_blank" data-outlook-id="56823feb-9b2d-4af9-bf02-79cfa0fe5212" moz-do-not-send="true">
https://www.open-std.org/jtc1/sc22/wg14/issues/</a>.
Essentially you need to email the issue to
<a href="mailto:c-issues@open-std.org" target="_blank" data-outlook-id="44dc4dc1-a175-4fd9-83a9-230568621882" moz-do-not-send="true" class="moz-txt-link-freetext">
c-issues@open-std.org</a>.</div>
</blockquote>
<div class="gmail_quote gmail_quote_container" style="direction: ltr;"><br>
</div>
<div class="gmail_default" style="direction: ltr; font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">
Thanks, I can do that, but first let's make sure we're on the
same page.</div>
<blockquote style="margin: 0px 0px 0px 0.8ex; padding-left: 1ex; border-left-width: 1px; border-left-style: solid; border-left-color: rgb(204, 204, 204);">
<div class="gmail_quote" style="direction: ltr; font-family: Aptos, Arial, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);">
For this particular issue, I believe the value for the SNaN
is the payload and that is unchanged. The operation still
raises “invalid” as expected from any operation (including
conversion) other than the very small set that explicitly do
not do so (ex. The issignaling macro).</div>
</blockquote>
<div class="gmail_quote gmail_quote_container" style="direction: ltr;"><br>
</div>
<div class="gmail_quote gmail_quote_container" style="direction: ltr;">F<span style="font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">irstly,
ISO/IEC 60559 merely recommends that NaN payloads are
propagated. §6.2.3 is full of "should". It would be
extremely surprising if the C requirement EVEN for
implementations that don't conform to Annex F was stricter
than ISO/IEC 60559. That can't be right, but the wording
says the value is unchanged, and you're reading "value" as
synonymous with NaN payload.</span></div>
<div class="gmail_quote gmail_quote_container" style="direction: ltr; font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">
<br>
</div>
<div class="gmail_quote gmail_quote_container" style="direction: ltr;"><span style="font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">Secondly,
I don't know why you would read that as being synonymous
here. "value" as defined in §3.24 is the "</span>precise
meaning of the contents of an object when interpreted as
having a specific type<span style="font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">".
It's a C construct derived from contents of an object, so
when the C wording requires that a "value" is unchanged, I'm
reading that as an sNaN not turning into a qNaN since those
are two different values. However, the underlying hardware
operation does turn sNaNs into qNaNs, and so does the
convertFormat operation in ISO/IEC 60559, so I'm not finding
any way to read the C wording as non-defective.</span></div>
<div class="gmail_quote gmail_quote_container" style="direction: ltr; font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">
<br>
</div>
<div class="gmail_quote gmail_quote_container" style="direction: ltr; font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">
Anyway, I'm not really an expert, so I'd be happy if you could
elaborate on this before I go and report to someone else :)</div>
<div class="gmail_quote gmail_quote_container" style="direction: ltr; font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">
<br>
</div>
<div class="gmail_quote gmail_quote_container" style="direction: ltr; font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">
<br>
</div>
<div class="gmail_quote gmail_quote_container" style="direction: ltr; font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">
Yours</div>
<div class="gmail_quote gmail_quote_container" style="direction: ltr; font-family: arial, helvetica, sans-serif; color: rgb(0, 0, 0);">
Jan</div>
</div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
<pre wrap="" class="moz-quote-pre">_______________________________________________
cfp-interest mailing list
<a class="moz-txt-link-abbreviated" href="mailto:cfp-interest@oakapple.net">cfp-interest@oakapple.net</a>
<a class="moz-txt-link-freetext" href="http://mailman.oakapple.net/mailman/listinfo/cfp-interest">http://mailman.oakapple.net/mailman/listinfo/cfp-interest</a>
</pre>
</blockquote>
<p><br>
</p>
</body>
</html>