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<p class="MsoNormal">In the first case (0.0/0.0) clang’s constant folder gets rid of the division and replaces it with clang’s default representation of NaN. In the second case (0.0/bla) because you’ve declared ‘bla’ as volatile we actually perform the division,
so the NaN in that case comes from the processor.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">-Andy<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><a name="_____replyseparator"></a><b>From:</b> cfe-dev <cfe-dev-bounces@lists.llvm.org>
<b>On Behalf Of </b>Gaier, Bjoern via cfe-dev<br>
<b>Sent:</b> Tuesday, February 05, 2019 1:33 AM<br>
<b>To:</b> cfe-dev@lists.llvm.org<br>
<b>Subject:</b> [cfe-dev] Clang-Cl - Representation of NAN; Code to reproduce<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoPlainText">I discovered something new, that is interesting:<o:p></o:p></p>
<p class="MsoPlainText">When I compile:<o:p></o:p></p>
<p class="MsoPlainText"> <o:p></o:p></p>
<p class="MsoPlainText">volatile const double result = 0.0/0.0;<o:p></o:p></p>
<p class="MsoPlainText">This will result in "0x7FF8000000000000"<o:p></o:p></p>
<p class="MsoPlainText"> <o:p></o:p></p>
<p class="MsoPlainText">But:<o:p></o:p></p>
<p class="MsoPlainText">volatile const double bla = 0.0;<o:p></o:p></p>
<p class="MsoPlainText">volatile const double result = 0.0/bla;<o:p></o:p></p>
<p class="MsoPlainText">Will result in "0xFFF8000000000000"<o:p></o:p></p>
<p class="MsoPlainText"> <o:p></o:p></p>
<p class="MsoPlainText">Both compiled with Clang of course!<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><b>From:</b> cfe-dev <<a href="mailto:cfe-dev-bounces@lists.llvm.org">cfe-dev-bounces@lists.llvm.org</a>>
<b>On Behalf Of </b>Gaier, Bjoern via cfe-dev<br>
<b>Sent:</b> Dienstag, 5. Februar 2019 09:29<br>
<b>To:</b> <a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a><br>
<b>Subject:</b> [cfe-dev] Clang-Cl - Representation of NAN<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Hello everyone,<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">we are currently using clang-cl (build with LLVM7) in our project, which previously used the MSVC2017 compiler. We noticed a major difference with the representation of the NAN value.<o:p></o:p></p>
<p class="MsoNormal">Clang generates 0x7FF8000000000000 for an NAN<o:p></o:p></p>
<p class="MsoNormal">MSVC generates 0xFFF8000000000000 for an NAN<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">This difference leads to problems with C#, because it interacts with our C++ code and 'misses' the NAN.<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Is there a way to change the representation of the NAN via a compiler flag?<o:p></o:p></p>
<p class="MsoNormal">Could we also change the source code of clang to force this representation of NAL? Or is this to much effort for a workaround?<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
<p class="MsoNormal">Kind greetings<o:p></o:p></p>
<p class="MsoNormal">Björn<o:p></o:p></p>
<p class="MsoNormal">Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816, USt.ID-Nr. DE 114 165 789 Geschäftsführer: Dr. Hiroshi Nakamura, Dr. Robert Plank, Markus Bode, Heiko Lampert, Takashi Nagano, Takeshi Fukushima. Junichi Tajika
<o:p></o:p></p>
<p class="MsoNormal">Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816, USt.ID-Nr. DE 114 165 789 Geschäftsführer: Dr. Hiroshi Nakamura, Dr. Robert Plank, Markus Bode, Heiko Lampert, Takashi Nagano, Takeshi Fukushima. Junichi Tajika
<o:p></o:p></p>
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