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    <body><span class="vcard"><a class="email" href="mailto:mclow.lists@gmail.com" title="Marshall Clow (home) <mclow.lists@gmail.com>"> <span class="fn">Marshall Clow (home)</span></a>
</span> changed
              <a class="bz_bug_link 
          bz_status_RESOLVED  bz_closed"
   title="RESOLVED INVALID - incorrect implementation of isnan and similar functions"
   href="https://llvm.org/bugs/show_bug.cgi?id=18218">bug 18218</a>
        <br>
             <table border="1" cellspacing="0" cellpadding="8">
          <tr>
            <th>What</th>
            <th>Removed</th>
            <th>Added</th>
          </tr>

         <tr>
           <td style="text-align:right;">Status</td>
           <td>ASSIGNED
           </td>
           <td>RESOLVED
           </td>
         </tr>

         <tr>
           <td style="text-align:right;">Resolution</td>
           <td>---
           </td>
           <td>INVALID
           </td>
         </tr></table>
      <p>
        <div>
            <b><a class="bz_bug_link 
          bz_status_RESOLVED  bz_closed"
   title="RESOLVED INVALID - incorrect implementation of isnan and similar functions"
   href="https://llvm.org/bugs/show_bug.cgi?id=18218#c7">Comment # 7</a>
              on <a class="bz_bug_link 
          bz_status_RESOLVED  bz_closed"
   title="RESOLVED INVALID - incorrect implementation of isnan and similar functions"
   href="https://llvm.org/bugs/show_bug.cgi?id=18218">bug 18218</a>
              from <span class="vcard"><a class="email" href="mailto:mclow.lists@gmail.com" title="Marshall Clow (home) <mclow.lists@gmail.com>"> <span class="fn">Marshall Clow (home)</span></a>
</span></b>
        <pre>(In reply to <a href="show_bug.cgi?id=18218#c0">comment #0</a>)

<span class="quote">> The template should be enabled for every type that is convertible to an
> arithmetic type, to make the implementation indistinguishable from what is
> specified in the standard.</span >

After some research, and talking to a bunch of people, I have come to the
conclusion that this is incorrect.

This is LWG issue #2086 - <a href="http://cplusplus.github.io/LWG/lwg-defects.html#2086">http://cplusplus.github.io/LWG/lwg-defects.html#2086</a>,
and the discussion there is quite clear: 

      The only valid types that can be passed to isnan (and others in <cmath>)
are arithmetic types; i.e, the built-in integral and floating point types. No
user-defined types.</pre>
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