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Description
| Bugzilla Link | 46373 |
| Version | unspecified |
| OS | All |
| CC | @mclow |
Extended Description
Instantiating a
std::linear_congruential_engine<UIntType, a, c, m>
with a value 0 for "m" indicates that the linear congruential engine should use the full size of the UIntType, instead of explicitly performing a mod operation after each iteration.
While most of the code for std::linear_congruential_engine appears to correctly handle m == 0, attempting to seed the engine from a generator triggers a divide by zero:
#include <random>
#include <stdint.h>
std::random_device device;
std::seed_seq seq{device(), device()};
std::linear_congruential_engine<uint64_t, 6364136223846793005, 1442695040888963407, 0> rng(seq); // divide by zero
The problem appears to be in the "__seed" function inside the "random" header:
template <class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m>
template<class _Sseq>
void
linear_congruential_engine<_UIntType, __a, __c, __m>::__seed(_Sseq& __q,
integral_constant<unsigned, 2>)
{
const unsigned __k = 2;
uint32_t __ar[__k+3];
__q.generate(__ar, __ar + __k + 3);
result_type __s = static_cast<result_type>((__ar[3] +
((uint64_t)__ar[4] << 32)) % __m);
__x_ = __c == 0 && __s == 0 ? result_type(1) : __s;
}
where we perform a "... % __m" operation without confirming that __m is non-zero.
I believe this could be resolved by only performing the mod when "__m != 0".
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Issues migrated from bugzillaIssues migrated from bugzillalibc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi.libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi.