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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - copysign(x, signbit(x) ? +1.f : -1.f) folding"
href="https://bugs.llvm.org/show_bug.cgi?id=44153">44153</a>
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<th>Summary</th>
<td>copysign(x, signbit(x) ? +1.f : -1.f) folding
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<tr>
<th>Keywords</th>
<td>code-quality
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>nok.raven@gmail.com
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<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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<div>
<pre>There is a problem with replacing boost's changesign:
#include <boost/math/special_functions/sign.hpp>
float changesign_boost(float x) {
return boost::math::changesign(x);
}
#include <cmath>
float changesign_std(float x) {
bool isneg = std::signbit(x);
return std::copysign(x, isneg ? +1.f : -1.f);
}
changesign_boost(float):
xorps xmm0, xmmword ptr [rip + .LCPI0_0]
ret
changesign_std(float):
movd eax, xmm0
xor ecx, ecx
test eax, eax
sets cl
pand xmm0, xmmword ptr [rip + .LCPI1_0]
movd xmm1, dword ptr [4*rcx + .LCPI1_1]
pand xmm1, xmmword ptr [rip + .LCPI1_2]
por xmm0, xmm1
ret
<a href="https://godbolt.org/z/AN2VfR">https://godbolt.org/z/AN2VfR</a></pre>
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