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<p class="MsoNormal">| And at runtime, on some targets, we use this:<o:p></o:p></p>
<p class="MsoNormal">|<o:p></o:p></p>
<p class="MsoNormal">| <a href="https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/builtins/floatuntisf.c">
https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/builtins/floatuntisf.c</a><o:p></o:p></p>
<p class="MsoNormal">|<o:p></o:p></p>
<p class="MsoNormal">| ... which gives a NaN in this case.<o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I copied that function into a test program on Ubuntu, built with gcc, and it gives me +Infinity (0x7f800000) not NaN (0x7fc00000).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> metafoo@gmail.com [mailto:metafoo@gmail.com]
<b>On Behalf Of </b>Richard Smith<br>
<b>Sent:</b> Tuesday, December 08, 2015 11:42 AM<br>
<b>To:</b> Robinson, Paul<br>
<b>Cc:</b> Joerg Sonnenberger; cfe-commits (cfe-commits@lists.llvm.org)<br>
<b>Subject:</b> Re: r254574 - PR17381: Treat undefined behavior during expression evaluation as an unmodeled<o:p></o:p></span></p>
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<p class="MsoNormal">On Tue, Dec 8, 2015 at 11:18 AM, Richard Smith <<a href="mailto:richard@metafoo.co.uk" target="_blank">richard@metafoo.co.uk</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">On Tue, Dec 8, 2015 at 10:59 AM, Robinson, Paul <<a href="mailto:Paul_Robinson@playstation.sony.com" target="_blank">Paul_Robinson@playstation.sony.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Okay, I'll bite: so what *does* UINT128_MAX actually convert to?</span><o:p></o:p></p>
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<p class="MsoNormal">$ echo 'unsigned __int128 max = -1; float f = max;' | ~/clang-8/build/bin/clang -x c++ - -emit-llvm -S -o - -O3 | grep @f<o:p></o:p></p>
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<p class="MsoNormal">@f = global float undef, align 4<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">And at runtime, on some targets, we use this:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"> <a href="https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/builtins/floatuntisf.c">
https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/builtins/floatuntisf.c</a><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">... which gives a NaN in this case.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> cfe-commits [mailto:<a href="mailto:cfe-commits-bounces@lists.llvm.org" target="_blank">cfe-commits-bounces@lists.llvm.org</a>]
<b>On Behalf Of </b>Richard Smith via cfe-commits<br>
<b>Sent:</b> Tuesday, December 08, 2015 10:52 AM<br>
<b>To:</b> Joerg Sonnenberger; cfe-commits<br>
<b>Subject:</b> Re: r254574 - PR17381: Treat undefined behavior during expression evaluation as an unmodeled</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">On Tue, Dec 8, 2015 at 2:13 AM, Joerg Sonnenberger via cfe-commits <<a href="mailto:cfe-commits@lists.llvm.org" target="_blank">cfe-commits@lists.llvm.org</a>> wrote:<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">On Mon, Dec 07, 2015 at 01:32:14PM -0800, Richard Smith via cfe-commits wrote:<br>
> C11 <a href="http://6.3.1.5/1" target="_blank">6.3.1.5/1</a>: "If the value being converted is outside the range of values<br>
> that can be represented, the behavior is undefined."<br>
<br>
The value of 1e100 can be represented as +inf, even if not precisely.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Only if +inf is in the range of representable values, which, as already noted, is problematic.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">This is a bit different from non-IEEE math like VAX, that doesn't have<br>
infinities.<o:p></o:p></p>
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Joerg<br>
_______________________________________________<br>
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