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[libc++][NFC] Simplify the mersenne_twister_engine implementation a bit (#194893)

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This replaces some SFINAE and function overloading with `if
_LIBCPP_CONSTEXPR` to simplify the code a bit.
This commit is contained in:
Nikolas Klauser
2026-04-30 19:59:55 +02:00
committed by GitHub
parent 6810a69ab8
commit 229104763d
1 changed files with 31 additions and 49 deletions
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80
libcxx/include/__random/mersenne_twister_engine.h
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@@ -184,7 +184,25 @@ public:
}
template <class _Sseq, __enable_if_t<__is_seed_sequence<_Sseq, mersenne_twister_engine>::value, int> = 0>
_LIBCPP_HIDE_FROM_ABI void seed(_Sseq& __q) {
__seed(__q, integral_constant<unsigned, 1 + (__w - 1) / 32>());
const unsigned __k = 1 + (__w - 1) / 32;
static_assert(__k <= 2);
uint32_t __ar[__n * __k];
__q.generate(__ar, __ar + __n * __k);
for (size_t __i = 0; __i < __n; ++__i) {
if _LIBCPP_CONSTEXPR (__k == 1) {
__x_[__i] = static_cast<result_type>(__ar[__i] & _Max);
} else {
__x_[__i] = static_cast<result_type>((__ar[2 * __i] + ((uint64_t)__ar[2 * __i + 1] << 32)) & _Max);
}
}
const result_type __mask = __r == _Dt ? result_type(~0) : (result_type(1) << __r) - result_type(1);
__i_ = 0;
if ((__x_[0] & ~__mask) == 0) {
for (size_t __i = 1; __i < __n; ++__i)
if (__x_[__i] != 0)
return;
__x_[0] = result_type(1) << (__w - 1);
}
}
// generating functions
@@ -265,59 +283,23 @@ public:
mersenne_twister_engine<_UInt, _Wp, _Np, _Mp, _Rp, _Ap, _Up, _Dp, _Sp, _Bp, _Tp, _Cp, _Lp, _Fp>& __x);
private:
template <class _Sseq>
_LIBCPP_HIDE_FROM_ABI void __seed(_Sseq& __q, integral_constant<unsigned, 1>) {
const unsigned __k = 1;
uint32_t __ar[__n * __k];
__q.generate(__ar, __ar + __n * __k);
for (size_t __i = 0; __i < __n; ++__i)
__x_[__i] = static_cast<result_type>(__ar[__i] & _Max);
const result_type __mask = __r == _Dt ? result_type(~0) : (result_type(1) << __r) - result_type(1);
__i_ = 0;
if ((__x_[0] & ~__mask) == 0) {
for (size_t __i = 1; __i < __n; ++__i)
if (__x_[__i] != 0)
return;
__x_[0] = result_type(1) << (__w - 1);
template <size_t __count>
_LIBCPP_HIDE_FROM_ABI static result_type __lshift(result_type __x) {
if _LIBCPP_CONSTEXPR (__count < __w) {
return (__x << __count) & _Max;
} else {
return result_type(0);
}
}
template <class _Sseq>
_LIBCPP_HIDE_FROM_ABI void __seed(_Sseq& __q, integral_constant<unsigned, 2>) {
const unsigned __k = 2;
uint32_t __ar[__n * __k];
__q.generate(__ar, __ar + __n * __k);
for (size_t __i = 0; __i < __n; ++__i)
__x_[__i] = static_cast<result_type>((__ar[2 * __i] + ((uint64_t)__ar[2 * __i + 1] << 32)) & _Max);
const result_type __mask = __r == _Dt ? result_type(~0) : (result_type(1) << __r) - result_type(1);
__i_ = 0;
if ((__x_[0] & ~__mask) == 0) {
for (size_t __i = 1; __i < __n; ++__i)
if (__x_[__i] != 0)
return;
__x_[0] = result_type(1) << (__w - 1);
template <size_t __count>
_LIBCPP_HIDE_FROM_ABI static result_type __rshift(result_type __x) {
if _LIBCPP_CONSTEXPR (__count < _Dt) {
return __x >> __count;
} else {
return result_type(0);
}
}
template <size_t __count,
__enable_if_t<__count< __w, int> = 0> _LIBCPP_HIDE_FROM_ABI static result_type __lshift(result_type __x) {
return (__x << __count) & _Max;
}
template <size_t __count, __enable_if_t<(__count >= __w), int> = 0>
_LIBCPP_HIDE_FROM_ABI static result_type __lshift(result_type) {
return result_type(0);
}
template <size_t __count,
__enable_if_t<__count< _Dt, int> = 0> _LIBCPP_HIDE_FROM_ABI static result_type __rshift(result_type __x) {
return __x >> __count;
}
template <size_t __count, __enable_if_t<(__count >= _Dt), int> = 0>
_LIBCPP_HIDE_FROM_ABI static result_type __rshift(result_type) {
return result_type(0);
}
};
template <class _UInt,