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Optimized divisionless implementation of minstd #5256

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Optimized divisionless implementation of minstd #5256

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2b58429
Optimized divisionless implementation of minstd
mirounga Jan 27, 2025
33dcc0a
Formatting updates
mirounga Jan 28, 2025
7165215
switched to if constexpr
mirounga Jan 31, 2025
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28 changes: 28 additions & 0 deletions stl/inc/random
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Original file line number Diff line number Diff line change
Expand Up @@ -508,6 +508,34 @@ _NODISCARD _Uint _Next_linear_congruential_value(_Uint _Prev) noexcept {
}
}

// Optimized specialization for minstd_rand0
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template <>
_NODISCARD inline unsigned int _Next_linear_congruential_value<unsigned int, 16807, 0, 2147483647>(
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unsigned int _Prev) noexcept {
constexpr unsigned long long _All = 16807ULL;
constexpr unsigned long long _Mll = 2147483647ULL;

auto _Next = static_cast<unsigned long long>(_Prev) * _All;
_Next = (_Next >> 31) + (_Next & _Mll);
_Next = _Next < _Mll ? _Next : _Next - _Mll;

return static_cast<unsigned int>(_Next);
}

// Optimized specialization for minstd_rand
template <>
_NODISCARD inline unsigned int _Next_linear_congruential_value<unsigned int, 48271, 0, 2147483647>(
unsigned int _Prev) noexcept {
constexpr unsigned long long _All = 48271ULL;
constexpr unsigned long long _Mll = 2147483647ULL;

auto _Next = static_cast<unsigned long long>(_Prev) * _All;
_Next = (_Next >> 31) + (_Next & _Mll);
_Next = _Next < _Mll ? _Next : _Next - _Mll;

return static_cast<unsigned int>(_Next);
}

template <class _Seed_seq>
_NODISCARD constexpr unsigned int _Seed_seq_to_uint(_Seed_seq& _Seq) {
unsigned int _Arr[4]{};
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