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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - std::uniform_int_distribution<__int128_t>{INT64_MIN, INT64_MAX} produces out-of-range values"
href="https://bugs.llvm.org/show_bug.cgi?id=51520">51520</a>
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<th>Summary</th>
<td>std::uniform_int_distribution<__int128_t>{INT64_MIN, INT64_MAX} produces out-of-range values
</td>
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<th>Product</th>
<td>libc++
</td>
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<th>Version</th>
<td>12.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>All Bugs
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>moritz.klammler@cetitec.com
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
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<p>
<div>
<pre>The specific std::uniform_int_distribution<__int128_t>{INT64_MIN, INT64_MAX}
produces values that are not in range. Changing any of the parameters -- e.g.
using std::int64_t as type or making either of the limits smaller or larger --
causes the problem to go away. The incorrect values are completely
out-of-range, not marginal off-by-one errors.
I have created the following test program and could reproduce the issue with
every version of libc++ and set of compiler options I've tried; the problem
never occurs with -stdlib=libstdc++ so it seems to me to be a library rather
than a compiler issue.
<a href="https://godbolt.org/z/z5WYsKEv6">https://godbolt.org/z/z5WYsKEv6</a>
This is a minimal version (with no output) of the demo linked above to
reproduce the problem:
#include <cstdint>
#include <cstdlib>
#include <random>
int main()
{
auto engine = std::default_random_engine{};
auto distro = std::uniform_int_distribution<__int128_t>{INT64_MIN,
INT64_MAX};
for (auto i = 0; i < 1000; ++i) {
const auto n = distro(engine);
if ((n < distro.min()) || (n > distro.max())) {
return EXIT_FAILURE;
}
}
return EXIT_SUCCESS;
}</pre>
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