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Add helper method for reliable uniform int for unit tests

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Signed-off-by: Arne Schwabe <arne@openvpn.net>
This commit is contained in:
Arne Schwabe 2023-11-09 16:00:20 +01:00
parent 95b821a2fd
commit 2910164ebf
1 changed files with 42 additions and 0 deletions
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42
test/unittests/test_helper.hpp
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@ -375,6 +375,48 @@ class FakeSecureRand : public openvpn::StrongRandomAPI
unsigned char next;
};
class unit_test_uniform_int_distribution
{
/* std::uniform_int_distribution is unfortunately implementation specific and generates different
* random numbers on different platforms. So use our own implementation to guarantee it for the unit tests.
*
* Based on https://arxiv.org/abs/1805.10941
*
* No guarantees that it is implemented correctly but even a bad implementation is good enough for unit tests
* if it is deterministic */
public:
template <typename generator>
uint32_t operator()(generator &prng)
{
/* Get random number in (0, range) first */
uint32_t range = B - A + 1;
uint64_t product = uint64_t{prng()} * uint64_t{range};
uint32_t low = static_cast<uint32_t>(product);
if (low < range)
{
uint32_t threshold = -range % range;
while (low < threshold)
{
product = uint64_t{prng()} * uint64_t{range};
low = static_cast<uint32_t>(product);
}
}
return A + (product >> 32u);
}
explicit unit_test_uniform_int_distribution(uint32_t low = 0, uint32_t high = std::numeric_limits<uint32_t>::max())
: A(low), B(high)
{
}
std::uint32_t A;
std::uint32_t B;
};
// googletest is missing the ability to test for specific
// text inside a thrown exception, so we implement it here