https://bugs.llvm.org/show_bug.cgi?id=51520
Bug ID: 51520
Summary: std::uniform_int_distribution<__int128_t>{INT64_MIN,
INT64_MAX} produces out-of-range values
Product: libc++
Version: 12.0
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: All Bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
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.
https://godbolt.org/z/z5WYsKEv6
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;
}
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