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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - std::uniform_int_distribution erroneously rejects generator values"
href="https://bugs.llvm.org/show_bug.cgi?id=39209">39209</a>
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<th>Summary</th>
<td>std::uniform_int_distribution erroneously rejects generator values
</td>
</tr>
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<th>Product</th>
<td>libc++
</td>
</tr>
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<th>Version</th>
<td>6.0
</td>
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<th>Hardware</th>
<td>All
</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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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>All Bugs
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>llvm@christoph-conrads.name
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=20974" name="attach_20974" title="Demonstration of bug">attachment 20974</a> <a href="attachment.cgi?id=20974&action=edit" title="Demonstration of bug">[details]</a></span>
Demonstration of bug
Given a generator returning values in the interval [0, r] and
`std::uniform_int_distribution(0, b)`, let r,b such that r+1 multiple of b+1.
In this case `std::uniform_int_distribution` may erroneously reject generator
values although no rejection sampling is needed.
In the demonstration program in the attachment, r=19, b=9 so that half of all
generator values are rejected. The bug does not occur if r+1 and b+1 are powers
of two.
Note that the GNU C++ Library contains a similar bug:
<a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80977">https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80977</a>
$ clang++ --version
clang version 6.0.1 (tags/RELEASE_601/final)
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/lib/llvm/6/bin</pre>
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