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<body><span class="vcard"><a class="email" href="mailto:richard-llvm@metafoo.co.uk" title="Richard Smith <richard-llvm@metafoo.co.uk>"> <span class="fn">Richard Smith</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED DUPLICATE - x87 single precision float underflow hidden (by incorrect double precision store?)"
href="https://llvm.org/bugs/show_bug.cgi?id=26931">bug 26931</a>
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<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>NEW
</td>
<td>RESOLVED
</td>
</tr>
<tr>
<td style="text-align:right;">CC</td>
<td>
</td>
<td>richard-llvm@metafoo.co.uk
</td>
</tr>
<tr>
<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>DUPLICATE
</td>
</tr></table>
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED DUPLICATE - x87 single precision float underflow hidden (by incorrect double precision store?)"
href="https://llvm.org/bugs/show_bug.cgi?id=26931#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED DUPLICATE - x87 single precision float underflow hidden (by incorrect double precision store?)"
href="https://llvm.org/bugs/show_bug.cgi?id=26931">bug 26931</a>
from <span class="vcard"><a class="email" href="mailto:richard-llvm@metafoo.co.uk" title="Richard Smith <richard-llvm@metafoo.co.uk>"> <span class="fn">Richard Smith</span></a>
</span></b>
<pre>(In reply to <a href="show_bug.cgi?id=26931#c0">comment #0</a>)
<span class="quote">> int main(void)
> {
> float x;
> feclearexcept(FE_ALL_EXCEPT);
> x = foo();
> if (fetestexcept(FE_UNDERFLOW))
> printf("FE_UNDERFLOW: ");
> printf("x = %e\n", x);
> return 0;
> }</span >
This testcase has undefined behavior. You can't use these fe* functions outside
of a region marked with #pragma STDC FENV_ACCESS ON.
See C11 7.6.1/2: "If part of a program tests floating-point status flags, sets
floating-point control modes, or runs under non-default mode settings, but was
translated with the state for the FENV_ACCESS pragma โโoffโโ, the behavior is
undefined."
Clang doesn't yet support #pragma FENV_ACCESS, which is PR8100.
*** This bug has been marked as a duplicate of <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - clang/llvm don't support C99 FP rounding mode pragmas (FENV_ACCESS etc)"
href="show_bug.cgi?id=8100">bug 8100</a> ***</pre>
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