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refactor generate_canonical #2452

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refactor generate_canonical #2452

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8ac4869
refactor generate_canonical
CaseyCarter Jan 1, 2022
0d6916c
Merge branch 'main' into canon
CaseyCarter Jan 20, 2022
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60 changes: 44 additions & 16 deletions stl/inc/random
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Original file line number Diff line number Diff line change
Expand Up @@ -238,32 +238,60 @@ private:
vector<result_type> _Myvec;
};

template <class _Real, size_t _Minbits, class _Result, _Result _Ix>
_NODISCARD constexpr int _Generate_canonical_helper() {
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@AlexGuteniev AlexGuteniev Jan 1, 2022

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"Helper" names aren't actually helpful. Maybe _Generate_canonical_times_ceil() ?

if constexpr ((_Ix & (_Ix - 1)) == 0) {
constexpr auto _Log2 = _STD _Countr_zero(_Ix);
return static_cast<int>((_Minbits + _Log2 - 1) / _Log2);
} else {
return static_cast<int>(_STD ceil(_Minbits / _STD log2(_Ix)));
}
}

template <class _Real, size_t _Bits, class _Gen>
_NODISCARD _Real generate_canonical(_Gen& _Gx) { // build a floating-point value from random sequence
_NODISCARD _Real generate_canonical(_Gen& _Gx) {
_RNG_REQUIRE_REALTYPE(generate_canonical, _Real);

const size_t _Digits = static_cast<size_t>(numeric_limits<_Real>::digits);
const size_t _Minbits = _Digits < _Bits ? _Digits : _Bits;
constexpr auto _Digits = static_cast<size_t>(numeric_limits<_Real>::digits);
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@AlexGuteniev AlexGuteniev Jan 1, 2022

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(Pre existing) convert with {} as you changed _NRAND to do so.

constexpr size_t _Minbits = _Digits < _Bits ? _Digits : _Bits;

if constexpr (is_integral_v<typename _Gen::result_type>) {
constexpr auto _Ix = (_Gen::max)() - (_Gen::min)() + 1;
const int _Ceil = _Generate_canonical_helper<_Real, _Minbits, typename _Gen::result_type, _Ix>();
#pragma warning(suppress : 6326) // Potential comparison of a constant with another constant
const int _Kx = _Ceil < 1 ? 1 : _Ceil;

const _Real _Gxmin = static_cast<_Real>((_Gx.min)());
const _Real _Gxmax = static_cast<_Real>((_Gx.max)());
const _Real _Rx = (_Gxmax - _Gxmin) + _Real{1};
_Real _Ans{0};
_Real _Factor{1};
constexpr auto _Gxmin = (_Gen::min)();
constexpr auto _Rx = static_cast<_Real>((_Gen::max)() - _Gxmin) + 1;

const int _Ceil = static_cast<int>(_STD ceil(static_cast<_Real>(_Minbits) / _STD log2(_Rx)));
const int _Kx = _Ceil < 1 ? 1 : _Ceil;
for (int _Idx = 0; _Idx < _Kx; ++_Idx) { // add in another set of bits
_Ans += static_cast<_Real>(_Gx() - _Gxmin) * _Factor;
_Factor *= _Rx;
}

_Real _Ans{0};
_Real _Factor{1};
return _Ans / _Factor;
} else { // We still need to tolerate TR1-era engines
const auto _Gxmin = static_cast<_Real>((_Gx.min)());
const auto _Gxmax = static_cast<_Real>((_Gx.max)());
const auto _Rx = (_Gxmax - _Gxmin) + _Real{1};

for (int _Idx = 0; _Idx < _Kx; ++_Idx) { // add in another set of bits
_Ans += (static_cast<_Real>(_Gx()) - _Gxmin) * _Factor;
_Factor *= _Rx;
}
const auto _Ceil = static_cast<int>(_STD ceil(_Minbits / _STD log2(_Rx)));
const int _Kx = _Ceil < 1 ? 1 : _Ceil;

return _Ans / _Factor;
_Real _Ans{0};
_Real _Factor{1};
for (int _Idx = 0; _Idx < _Kx; ++_Idx) { // add in another set of bits
_Ans += (static_cast<_Real>(_Gx()) - _Gxmin) * _Factor;
_Factor *= _Rx;
}

return _Ans / _Factor;
Comment on lines +283 to +290
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@AlexGuteniev AlexGuteniev Jan 1, 2022

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This repeats the above block, can it be fused?

}
}

#define _NRAND(eng, resty) (_STD generate_canonical<resty, static_cast<size_t>(-1)>(eng))
#define _NRAND(eng, resty) (_STD generate_canonical<resty, ~size_t{0}>(eng))

_INLINE_VAR constexpr int _MP_len = 5;
using _MP_arr = uint64_t[_MP_len];
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