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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Clang should support _BitscanForward and _BitscanForward64 in constant expressions"
href="https://bugs.llvm.org/show_bug.cgi?id=37062">37062</a>
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<th>Summary</th>
<td>Clang should support _BitscanForward and _BitscanForward64 in constant expressions
</td>
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<th>Product</th>
<td>clang
</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>Windows NT
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C++
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>billy.oneal@gmail.com
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<th>CC</th>
<td>dgregor@apple.com, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>In MSVC++'s STL, we implemented binary GCD as this can be faster, as it
replaces divisions with bsf. Unfortunately, right now we had to fake bsf with a
loop, resulting in std::gcd actually being slower than a naïve Euclid's
algorithm implementation. This could be substantially faster with real bsf.
Note that C1XX doesn't currently support _BitscanForward in constexpr contexts;
this bug is being filed at the same time it's being filed against C1XX (and
EDG).</pre>
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