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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Undefined behavior in StdLibExtras.h, bitCount"
href="https://bugs.webkit.org/show_bug.cgi?id=160565">160565</a>
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<th>Summary</th>
<td>Undefined behavior in StdLibExtras.h, bitCount
</td>
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<th>Classification</th>
<td>Unclassified
</td>
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<th>Product</th>
<td>WebKit
</td>
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<th>Version</th>
<td>WebKit Nightly Build
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<th>Hardware</th>
<td>Unspecified
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<th>OS</th>
<td>Unspecified
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>Normal
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<th>Priority</th>
<td>P2
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<th>Component</th>
<td>WebCore Misc.
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<th>Assignee</th>
<td>webkit-unassigned@lists.webkit.org
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<th>Reporter</th>
<td>jbedard@apple.com
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<pre>In StdLibExtras.h bitCount, there is undefined behavior on return. The line:
return (((bits + (bits >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24
almost always has undefined behavior. In this case, the overflow is expected. However, compiler optimization (given that this function is an inline) with constants may preform unexpected operations</pre>
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