<html>
    <head>
      <base href="https://bugs.llvm.org/">
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <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>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Clang should support _BitscanForward and _BitscanForward64 in constant expressions
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>trunk
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Windows NT
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>enhancement
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>C++
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>billy.oneal@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>dgregor@apple.com, llvm-bugs@lists.llvm.org
          </td>
        </tr></table>
      <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>
        </div>
      </p>


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